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Before metallic ores are worked upon in the large way, it will be necessary to inquire what sort of metal, and what portion of it, is to be found in a determinate quantity of the ore; to discover whether it will be worth while to extract it largely and in what manner the process is to be conducted, so as to answer that purpose. The knowledge requisite for this is called the art of assaying.
The assaying of ores may be performed either in the dry or moist way; the first is the most ancient, and, in many respects the most advantagageous, and consequently still continues to be mostly used.
Assays are made either in crucibles with the blast of the bellows, or in tests under a muffle.
The assay weights are always imaginary, sometimes an ounce represents a hundredweight on the large scale, and is subdivided into the same number of parts, as that hundredweight is in the great; so that the contents of the ore, obtained by the assay, shall accurately determine by such relative proportion the quantity to be expected from any weight of the ore on a larger scale.
In the lotting of the ores care should be taken to have small portions from different specimens, which should be pulverized, and well mixed in an iron or brass mortar. The proper quantity of the ore is now taken, and if it contain either sulphur or arsenic it is put into a crucible or test, and exposed to a moderate degree of heat, till no vapor arises from it. To assist this volatilization some add a small quantity of powdered charcoal.
To assist the fusion of the ores, and to convert the extraneous matters connected with them into scoria, assayers use different kinds of fluxes. The most usual and efficacious materials for the composition of these are, borax, cream of tartar, nitre, sal ammoniac, common salt, glass, fluro-spar, charcoal powder, pitch, lime, litharge, etc., in different proportions.
As the whole process of which we are speaking is merely an experiment, made for the purpose of ascertaining what is the nature of the metal contained in the ore, and the proportion the former bears to the latter, the little additional expense incurred by employing animal instead of vegetable charcoal is not to be regarded, particularly when the increased fusibility of the ore, occasioned thereby is considered.
This consists of 1 part of nitre and 2 of cream of tartar, well mixed together.
The above crude flux detonates by means of kindled charcoal, and if the detonation be effected in a mortar slightly covered it becomes black. It is a mixture of carbonate of potassa and charcoal.
Mix well together 10 oz. of cream of tartar, 3 oz. and 6 drs. of nitre, and 3 oz. and 1 dr. of borax.
Deflagrate, and afterwards pulverize, 2 parts of nitre and 1 part of cream of tartar.
The above fluxes answer the purpose very well provided the ores be deprived of all their sulphur, or if they contain much earthy matters; because, in the latter case, they unite with them, and convert them into a thin glass, but if any quantity of sulphur remain, these fluxes unite with it, and form a liver of sulphur, which has the power of destroying a portion of all the metals; consequently the assay under such circumstances must be very inaccurate. The principal difficulty in assaying appears to be in the appropriation of the proper fluxes to each particular ore, and it likewise appears that such a discriminating knowledge can only be acquired from an extensive practice, or from a knowledge of the chemical affinities and actions of different bodies upon each other.
In assaying we are at liberty to use the most expensive materials to effect our purpose, hence the use of different saline fluxes; but in the working at large such expensive means cannot be applied, as by such processes the inferior metals would be too much enhanced in value, especially in working very poor ores. In consequence of which in smelting works, where the object is the production of metals in the great way, cheaper additions are used, such as limestone, feldspar, fluor-spar, quartz sand, slate, and slags. These are to be chosen according to the different views of the operator and the nature of the ores. Thus iron ores, on account of the argillaceous earth they contain, require calcareous additions, and the copper ores, rather slags or vitrescent stones, than calcareous earth.
The mode of assaying ores for their particular metals by the dry way is deficient, so far as relates to pointing out the different substances connected with them, because they are always destroyed by the process for obtaining the assay metal. The essay by the moist way is more correct, because the different substances can be accurately ascertained.
Mix 100 grs. of the ore, thoroughly powdered, with from 30 to 100 grs. of calcined borax. The quality of the latter depends upon the quality of the ore, and is to be increased with the foreign matters. If the ore contains sulphur, it must first be roasted. The mixture is introduced into a crucible lined with charcoal, covered with powdered charcoal, on which is laid a piece of charcoal. The crucible is then closed, the cover luted on, and submitted to a white heat for an hour. The iron is found in the form of a button, and is not pure, but gives about the quality of the pig iron which will be obtained from the ore.
Fuch's method is accurate, and determines the relative quantity of protoxide and peroxide in an ore, which is often desirable. The only ores to which it cannot be applied are those containing arsenious acid, and this is not a very common ingredient.
Dissolve the ore in muriatic acid, and filter. Put into a small round-bottomed flask, and cork tightly until ready to boil it. Immerse a clean, weighed strip of copper, and, removing the cork, boil until the copper is no longer attacked. It is then taken out, washed, well wiped, and weighed. To ascertain the amount of peroxide multiply this weight by 40 and divide by 317. The quotient gives the amount sought.
To know the whole amount of iron in the ore, another portion is weighed out - say 1 gramme (about 15 grs.) - and dissolved as before; it is then digested with chlorate of potassa, by which all the iron is converted into peroxide, after which copper will decompose the whole. Multiply the loss by 28 and divide by 317; the quotient will give the whole amount of iron in the ore.
The presence of copper in the ore will make it appear poorer than it really is.
Heat 10 grs. of iron-ore, finely pulverized, with strong hydrochloric acid, for 1/2 an hour, in a conicalshaped flask with a funnel inserted in the neck; when decomposition is complete dilute the solution with water acidulated with sulphuric acid, and add a few pieces of granulated zinc and boil until all traces of yellow color disappear, or the solution remains of a pale green tint, and free from fine particles of zinc. Transfer to a white porcelain dish, and dilute to 20 oz. with distilled water.
When cold it is ready for testing with the following solution.
Dissolve 50 grs. of crystallized permanganate of potassa in 20 oz. of distilled water, and keep it in a tightly corked bottle, marked "Standard Solution Permanganate of Potassa." To ascertain the standard of this solution, dissolve 10 grs. of iron piano wire in dilute hydrochloric acid in a narrow-mouth flask with gentle heat. Dilute to 10 oz. Take 1 oz. of the diluted iron solution and dilute to 20 oz. with distilled water in a white porcelain dish.
Allow the solution of permanganate to run slowly in from a graduated pipette, stirring constantly until the solution assumes a faint pink color. Record the amount used; this represents 1 gr. of metallic iron.
Proceed in the same manner to test the solution of ore first obtained, noting the amount required to produce the first tint of pink color. Divide this amount by the amounts required for 1 gr. of iron, and the result is the number of grains of metallic iron contained in the ore.
Mix a quintal of tin ore, previously washed, pulverized, and roasted till no arsenical vapor arises, with half a quintal of calcined borax, and the same quantity of pulverized pitch; these are to be put in a crucible lined with charcoal, which is placed in an air-furnace. After the pitch is burnt, give a violent heat for a quarter of an hour, and on withdrawing the crucible, the regulus will be found at the bottom. If the ore be not well washed from earthy matters, a larger quantity of borax will be requisite, with some powdered glass, and if the ore contain iron, some alkaline salt may be added.
Dissolve the ore in hot muriatic acid, pass through the solution a current of sulphuretted hydrogen in large excess. Allow the precipitate to subside; add to it, with the aid of heat, nitric acid until no sulphuretted hydrogen is given off. This transforms the tin into stannic acid; wash carefully, dry, and weigh. Stannic acid contains 78.61 per cent. of tin.
As most of the lead ores contain either sulphur or arsenic, they require to be well roasted. Take a quintal of roasted ore, with the same quantity of calcined borax, 1/2 a quintal of fine powdered glass, 1/4 of a quintal of pitch and as much clean iron filings. Line the crucible with wetted charcoal-dust, and put the mixture into the crucible, and place it before the bellows of a forge-fire. When it is red hot, raise the fire for 15 or 20 minutes, then withdraw the crucible, and break it when cold.
Powder the ore (Galena) finely. Moisten with fuming nitric acid and digest on the sand-bath. This converts the whole into sulphate of lead. Dilute with water and filter. The insoluble sulphate of lead will remain in the filter. Wash it thoroughly, dry it, and weigh - 100 parts of sulphate of lead contain 73.56 parts of oxide of lead and 68.28% of metallic lead.
Take the assay weight of roasted ore, and mix it well with one-eighth part of charcoal-dust, put it into a strong luted earthen retort, to which must be fitted a receiver; place the retort in a furnace and raise the fire, and continue it in a violent heat for two hours; suffer it then to cool gradually, and the zinc will be found adhering to the neck of the retort in its metallic form.
Take 20 grs. of the ore (finely pulverized) to be assayed. Digest it for 1 hour in nitric acid 1 part, water 2 parts, with a few drops of hydrochloric acid; add carbonate of ammonia dissolved in liquid ammonia until the reaction is strongly alkaline. Digest for half an hour, dilute with an equal bulk of distilled water; filter and mark the filtrate Sol. A.
Make a standard solution of zinc by dissolving 10 grs. of pure zinc in nitric acid and diluting to 10 oz. Sol. B.
Make a solution of sulphide of sodium, 1 oz. of saturated solution to 10 oz. of distilled water. Sol. C.
Take of solution chloride of iron, 1/2 oz.; distilled water, 5 oz.: add aqua ammonia, separate all of the iron. Shake. Sol. D.
Take of solution B. 1 oz.; dilute to 3 oz.; add of solutions D, 1 oz.; take in a graduated pipette of solution C, and add gradually to the mixture of B and D (stirring rapidly all the while), until the flocculent iron begins to change color to grayish black. Make a memorandum of the number of graduations of solution C required. This is the amount of sulphide of sodium necessary to precipitate 1 gr. of metallic zinc.
Take 1/2 of solution A (diluted to 12 oz.) equal 6 oz.; add of solution D, 2 oz.; then with graduated pipette run in slowly the solution C until the flocculent iron begins to change color as before. The number of graduations required, divided by the number used in the former experiment, indicate the number of grains of metallic zinc in 10 grs. of the ore, and represent the per centage likewise.
Take an exact troyounce of the ore, previously pulverized, and calcine it well; stir it all the time with an iron rod without removing it from the crucible; after the calcination add an equal quantity of borax, 1/2 the quantity of fusible glass, 1/4 the quantity of pitch, and a little charcoal-dust; rub the inner surface of the crucible with a paste composed of charcoal- dust, a little fine powdered clay, and water. Cover the mass with common salt, and put a lid upon the crucible, which is to be placed in a furnace; the fire is to be raised gradually till it burns briskly, and the crucible continued in it for 1/2 hour, stirring the metal frequently with an iron rod; and when the scoria which adheres to the rod appears clear, then the crucible must be taken out and suffered to cool, after which it must be broken and the regulus separated and weighed. This is called black copper; to refine which equal parts of common salt and nitre are to be well mixed together. The black copper is brought into fusion, and a teaspoonful of the flux is thrown upon it which is repeated 3 or 4 times, when the metal is poured into an ingot mould and the button is found to be fine copper.
Make a solution of vitreous copper ore in 5 times its weight of concentrated sulphuric acid and boil it to dryness; add as much water as will dissolve the vitriol thus formed. To this solution add a clean bar of iron, which will precipitate the whole of the copper in its metallic form. If the solution be contaminated with iron, the copper must be redissolved in the same manner and precipitated again. The sulphur may be separated by filtration.
Dissolve 10 grs. of the copper ore finely pulverized and moistened with strong sulphuric acid, in strong nitric acid, adding the acid gradually; and when the fumes of hyponitric acid cease to be evolved, add a small amount of water and boil for a few minutes. Dilute to 10 oz. and treat with ammonia in excess, and it will become of a deep blue color. Set aside to cool, and prepare the following solution: Dissolve 500 grs. of granulated cyanide of potassium in 20 oz. of distilled water, and keep in a tight-stoppered bottle in the dark. Mark "Standard Solution Cyanide of Potassium". To ascertain the standard of this solution, dissolve 10 grs. of electrotype copper in dilute nitric acid and boil to expel hyponitric acid fumes, and dilute to 10 oz. with distilled water. Take of this solution 1 oz. and dilute to 5 oz. with distilled water, and allow the standard cyanide solution to flow very slowly into it at intervals, from a graduated pipette, and note the amount used to render it nearly colorless. This process takes from 1/2 to 3/4 of an hour. Proceed in the same manner to test the solution of ore first obtained, noting the amount required to reduce the color to a faint lilac. Divide this amount by the amount found required for 1 gr. of metallic copper, and the result is the number of grains of metallic copper in the ore tested.
If the ore be mineralized by sulphur, or sulphur and iron, a previous roasting will be necessary. The strong ores require no roasting, but only to be reduce to a fine powder. Take the assay weight and mix it with half the quantity of calcined borax, and the same of pounded glass; line the crucible with charcoal, melt it as quickly as possible, and when well done, take out the crucible and let it cool gradually. The regulus will be found at the bottom.
Bismuth is easily soluble in nitric acid or aqua regia. Its solution is colorless and is precipitable by the addition of pure water; 118 grs. of the precipitate from nitric acid, well washed and dried, are equal to 100 of bismuth in its metallic form.
Take a common crucible, bore a number of small holes in the bottom, and place it in another crucible a size smaller, luting them well together; then put the proper quantity of ore in small lumps into the upper crucible, and lute thereon a cover; place these vessels on a hearth and surround them with stones about 6 in. distant from them, the intermediate space must be filled with ashes, so that the undermost crucible may be covered with them; but upon the upper charcoal must be laid and the whole made red hot by the assistance of hand bellows. The antimony being of easy fusion is separated, and runs through the holes of the upper vessel into the inferior one, where it is collected.
Dissolve the ore in aqua regia; the sulphur is seperated by filtration. Evaporate the solution to dryness and heat below redness until all the nitric acid is expelled. The resulting antimonic acid contains 76.33 per cent. of metallic antimony.
The regulus is obtained by mixing the calx or ore of manganese with oil, making it into a ball, and putting it into a crucible lined with powdered charcoal 1 10th of an inch on the sides, and 1/4 of an inch at bottom; then filling the empty space with charcoal- dust, covering the crucible with another inverted and luted on, and exposing it to the strongest heat of a forge for an hour or more. The ore is very difficult to reduce.
This assay is made by sublimation in close vessels. Beat the ore into small pieces and put them into a matrass, which place in a sand-pot with a proper degree of heat. The arsenic sublimes in this operation and adheres to the upper part of the vessel; when it must be carefully collected, with a view to ascertain its weight. A single sublimation will not be sufficient. It is better to perform the first sublimation with a moderate heat, and afterwards bruise the remainder and expose it to a stronger heat. The addition of charcoal is useful.
Digest the ore in muriatic acid, adding nitric by degrees, to help the solution. The sulphur will be found on the filter; the arsenic will remain in the solution, and may be precipitated in its metallic form by boiling with a strip of copper.
The ores must be well roasted to expel the sulphur and arsenic; the greener the calx proves during this torrefaction, the more it abounds in the nickel; but the redder it is, the more iron it contains. The proper quantity of this roasted ore is fused in an open crucible, with twice or thrice its weight of black flux, and the whole covered with common salt. By exposing the crucible to the strongest heat of a forge fire, and making the fusion complete, a regulus will be produced. This regulus is not pure, but contains a portion of arsenic, cobalt, and iron. Of the first it may be deprived by a fresh calcination, with the addition of powdered charcoal; and of the second by scorification. But it is with difficulty that it is entirely freed from the iron.
By solution in nitric acid it is freed from its sulphur; and by adding water to the solution, bismuth, if any, may be precipitated; as may silver, if contained it, by muriatic acid; and copper, when any, by iron.
To separate cobalt from nickel, the two oxides are dissolved in muriatic acid; the solution diluted with distilled water. The liquor is saturated with chlorine, and when gold, an excess of precipitated carbonate of baryta added. It is then set aside for 18 hours, when the cobalt will be precipitated as sesquioxide, while the nickel will remain in solution.
Free them as much as possible from earthy matters by well washing, and from sulphur and arsenic by roasting. The ore thus prepared is to be mixed with 3 parts of black flux, and a little decrepitated sea-salt; put the mixture in a lined crucible, cover it and place it in a forge-fire, or in a hot furnace, for this ore is very difficult of fusion.
When well fused, a metallic regulus will be found at the bottom, covered with a scoria of a deep blue color; as almost all cobalt ores contain bismuth, this is reduced by the same operation as the regulus of cobalt; but as they are incapable of chemically uniting together, they are always found distinct from each other in the crucible. The regulus of bismuth, having a greater specific gravity, is always at the bottom, and may be separated by a blow with a hammer.
Make a solution of the ore in nitric acid, or aqua regia, and evaporate to dryness; the residuum, treated with the acetic acid, will yield to it the cobalt; the arsenic should be first precipitated by the addition of water.
The calciform ores of mercury are easily reduced without any addition. A quintal of the ore is put into a retort, and a receiver luted on, containing some water; the retort is placed in a sand-bath, and a sufficient degree of heat given it, to force over the mercury which is condensed in the water of the receiver.
The sulphurous ores are assayed by distillation in the manner above, only these ores require an equal weight of clean iron-filings to be mixed with them, to disengage the sulphur, while the heat volatilizes the mercury, and forces it into the receiver. These ores should likewise be tried for cinnibar, to know whether it will answer the purpose of extracting it from them; for this a determinate quantity of the ore is finely powdered and put into a glass vessel, which is exposed to a gentle heat at first, and gradually increased till nothing more is sublimed. By the quantity thus acquired, a judgment may be formed whether the process will answer. Sometimes this cinnabar is not of so lively a color as that which is used in trade; in this case it may be refined by a second sublimation, and if it be still of too dark a color, it may be brightened by the addition of a quantity of mercury, and subliming it again.
The stony matrix should be dissolved in nitric acid, and the cinnabar being disengaged, should be boiled in 8 or 10 times its weight of aqua regia, composed of 3 parts of nitric, and 1 of muriatic acid. The mercury may be precipitated in the metallic form by zinc.
Take the assay quantity of the ore finely powdered, and roast it well in a proper degree of heat, frequently stirring it with an iron rod; then add to it about double the quantity of granulated lead, put it in a covered crucible, and place it in a furnace; raise the fire gently at first, and continue to increase it gradually, till the metal begins to work; if it should appear too thick, make it thinner by the addition of a little more lead; if the metal should boil too rapidly, the fire should be diminished. The surface will be covered by degrees with a mass of scoria, at which time the metal should be carefully stirred with an iron hook heated, especially towards the border, lest any of the ore should remain undissolved; and if what is adherent to the hook when raised from the crucible melts quickly again, and the extremity of the hook, after it is grown cold is covered with a thin, shining smooth crust, the scorification is perfect; but, on the contrary, if, while stirring it, any considerable clamminess is perceived in the scoria, and when it adheres to the hook, though red hot, and appears unequally tinged and seems dusty or rough, with grains interspersed here and there, the scorification is incomplete; in consequence of which the fire should be increased a little and what adheres to the hook should be gently beaten off, and returned with a small ladle into the crucible again. When the scorification is perfect, the metal should be poured into a cone, previously rubbed with a little tallow, and when it becomes cold, the scoria may be separated by a few strokes of a hammer. The button is the produce of the assay.
Take the assay quanitity of ore, roast and grind it with an equal portion of litharge, divide it into 2 or 3 parts, and wrap each up in a small piece of paper; put a cupel previously seasoned under a muffle, with about 6 times the quantity of lead upon it. When the lead begins to work, carefully put one of the papers upon it, and after this is absorbed, put on a second, and so on till the whole quantity is introduced; then raise the fire, and as the scoria is formed it will be taken up by the cupel, and at last the silver will remain alone. This will be the produce of the assay, unless the lead contains a small portion of silver, which may be discovered by putting an equal quantity of the same lead on another cupel, and working it off at the same time; if any silver be produced it must be deducted from the assay. This is called the witness.
Dissolve the ore or coin in nitric acid. Prepare a standard solution of common salt; 542.74 of common salt will precipitate 1000 parts of silver. It is convenient to have, also, solutions of 1-10th the standard strength for the final precipitations. Add the solution until no precipitate appears. From the amount of solution, and consequently of salt used, the amount of silver is at once determined without further weighing. To correct the result a standard silver solution is used at the same time, and any correction it may require is applied to the rest of the assay.
The general method of examining the purity of silver is by mixing it with a quantity of lead proportionate to the supposed portion of alloy; by testing this mixture, and afterwards weighing the remaining button of silver. This is the same process as refining silver by cupellation.
It is supposed that the mass of silver to be examined consists of 12 equal parts, called penny-weights, so that if an ingot weighs 1 oz., each of the parts will be 1-12th oz. Hence, if the mass of silver be pure, it is called silver of 12 dwts.; if it contain 1-12th of its weight of alloy, it is called silver of 11 dwts.; if 2-12ths of its weight be alloy it is called silver of 10 dwts, which parts of pure silver are galled 5 dwts. It must be observed here that assayers give the name cwt. to a weight equal to 24 real grs., which must not be confounded with their ideal weight. The assayers' grs. are galled fine grs. An ingot of fine silver, or silver of 12 dwts., contains, then, 288 fine grs.; if this ingot contain 1-288th of alloy, it is said to be silver of 11 dwts. and 23 grs.; if it contain 4-288th of alloy, it is said to be 11 dwts, 20 grs., etc. Now a certain real weight must be taken to represent the assay-weights; for instance, 36 real grs. represent 12 fine dwts.; this is subdivided into a sufficient number of other smaller weights, which also represent fractions of fine dwts. and grs. Thus, 18 real grs. represent 6 fine dwts, 3 real grs. represent 1 fine dwt., or 24 grs.; 1 1/2 real grs. represent 12 grs.; 1- 32d of a real gr. represents 1/4 of a fine gr., which is only 1-752d part of a mass of 12 cwt.
It is customary to make a double assay. The silver for the assay should be taken from opposite sides of the ingot, and tried on a touch stone. Assayers know pretty nearly the value of silver merely by the look of the ingot, and still better by the test of the torch-stone. The quantity of lead to be added is regulated by the portion of alloy, which being in general copper, will be nearly as follows:
Of silver:
| dwt, | gr. | dwt. | gr. | Requires from | |||||||
| From | { |
11 | 6 | to | - | - | 5 | to | 6 | } |
Times it's weight of lead. |
| 0 | 12 | to | - | - | 8 | to | 9 | ||||
| 19 | 18 | to | 9 | 0 | 12 | to | 13 | ||||
| 8 | 6 | to | 7 | 12 | 13 | to | 14 | ||||
| 6 | 18 | to | 6 | 0 | 14 | to | 15 | ||||
| 3 | 0 | to | 1 | 12 | 0 | to | 16 | ||||
| 1 | 12 | to | 0 | 18 | 0 | to | 20 | ||||
The cupel must be heated red-hot for half an hour before any metal is put upon them, by which all moisture is expelled. When the cupel is almost white by heat the lead is put into it, and the fire increased till the lead becomes redhot, smoking, and agitated by a motion of all its parts, called its circulation. Then the silver is to be put on the cupel, and the fire continued till the silver has entered the lead; and when the mass circulates well, the heat must be diminished by closing more or less the door of the assay furnace. The heat should be so regulated, that the metal on its surface may appear convex and ardent, while the cupel is less red; that the smoke shall rise to the roof of the muffle; that undulations shall be made in all directions; and that the middle of the metal shall appear smooth, with a small circle of litharge, which is continually imbibed by the cupel. By this treatment the lead and alloy will be entirely absorbed by the cupel, and the silver become bright and shining, when it is said to lighten; after which, if the operation has been well performed, the silver will be covered with rainbow colors, which quickly undulate and cross each other, and then the button becomes fixed and solid.
The diminution of weight shows the quantity of alloy. As all lead contains a small portion of silver, an equal weight with that used in the assay is tested off, and the product deducted from the assay-weight. This portion is called the witness. - Richardson's Metallic Arts.
The approximate weight of silver or gold in a nugget may be determined by calculation from its specific gravity. See MISCELLANEOUS.
That which is now most generally used is by amalgamation. The proper quantity is taken and reduced to a powder; about one-tenth of its weight of pure quicksilver is added, and the whole triturated in an iron mortar. The attraction subsisting between the gold and quicksilver, quickly unites them in the form of an amalgam, which is pressed through shamoy leather; the gold is easily separated from this amalgam, by exposure to a proper degree of heat, which evaporates the quicksilver, and leaves the gold. This evaporation should be made with luted vessels.
This is the foundation of all the operations by which gold is obtained from the rich mines of Peru, in South America.
Take a quantity of the gold-sand and heat it red-hot; quench it in water; repeat this two or three times, and the color of the sand will become a reddish brown. Then mix it with twice its weight of litharge, and revive the litharge into lead, by adding a small portion of charcoal-dust, and exposing it to a proper degree of heat; when the lead revives, it separates the gold from the sand; and the freeing of the gold from the lead must be afterwards performed by cupellation.
Another. - Bergmann assayed metallic ores containing gold, by mixing 2 parts of the ore, well pounded and washed, with 1 1/2 of litharge, and 3 of glass; covering the whole with common salt, and melting it in a smith's forge, in a covered crucible; he then opened the crucible, put a nail into it, and continued to do so till the iron was no longer attacked. The lead was thus precipitated which contained the gold, and was afterwards separated by cupellation.
Dissolve the ore in 12 times its weight of diluted nitric acid, gradually added; place it in a proper degree of heat; this takes up the soluble parts, and leaves the gold untouched, with the insoluble matrix, from which it may be separated by aqua regia. The gold may be again separated from the aqua regia by pouring ether upon it; the ether takes up the gold, and by being burnt off leaves it in its metallic state. The solution may contain iron, copper, manganese, calcareous earth, or argil; if it be evaporated to dryness, and the residuum heated to redness for 1/2 an hour, ammonia will extract the copper; fuming nitric acid the earths; the acetic acid the manganese; and the muriatic acid the oxide of iron. The sulphur floats on the first solution, from which it should be separated by filtration.
By this process gold and silver are separated from each other. These two metals equally resisting the action of fire and lead, must therefore be separated by other means. This is effected by different menstrua. Nitric acid, muriatic acid, and sulphur, which cannot attack gold, operate upon silver; and these are the principal agents employed in this process.
Parting by nitric acid is most convenient, consequently most used; indeed, it is the only one employed by goldsmiths. This is called simply parting.
That made by the muriatic acid is by cementation, and is called cemented parting; and parting by sulphur is made by fusion, and called dry parting
This process cannot succeed unless we attend to some essential circumstances: 1st. The gold and silver must be in a proper proportion, viz. the silver ought to be three parts to one of gold; though a mass containing two parts of silver to one of gold may be parted. To judge of the quality of the metal to be parted, assayers make a comparison upon a touchstone, between it and certain needles composed of gold and silver, in graduated proportions, and properly marked; which are called proof needles. If this trial shows that the silver is not to the gold as three to one, the mass is improper for the operation, unless more silver be added. And 2dly, that the parting may be exact, the aqua-fortis must be very pure, especially free from any mixture of the sulphuric or muriatic acid. For if this were not attended to, a quantity of silver proportional to these two foreign acids would be separated during the solution; and this quantity of silver would remain mingled with the gold, which consequently would not be entirely purified by the operation.
The gold and silver to be parted ought previously to be granulated by melting it in a crucible, and pouring it into a vessel of water, giving the water at the same time a rapid circular motion, by quickly stirring it round with a stick. The vessels generally used in this operation are called parting glasses, which ought to be very well annealed, and chosen free from flaws; as one of the chief inconveniences attending the operation is, that the glasses are apt to crack by exposure to gold, or even when touched by the hand. Some operators secure the bottom of the glasses by a coating composed of a mixture of new-slaked lime, with beer and whites of eggs, spread on a cloth, and wrapped round the glasses at the bottom; over which they apply a composition of clay and hair. The parting glasses should be placed in vessels containing water supported by trivets, with a fire under them; because if a glass should break, the contents are caught in the vessel of water. If the heat communicated to the water be too great, it may be properly regulated by pouring cold water gradually and carefully down the side of the vessel into a parting glass 15 inches high and 10 or 12 inches wide at the bottom; placed in a copper pan 12 inches wide at bottom, 15 inches wide at top, and 10 inches high, there is usually put about 80 oz. of metal, with twice as much of aqua-fortis.
The nitric acid ought to be of 22° B., afterwards of 32° B. Little heat should be applied at first, as the liquor is apt to swell and rise over the vessel; but when the acid is nearly saturated, the heat may safely be increased. When the solution ceases, which is known by the effervescence discontinuing, the liquor is to be poured off; if any grains appear entire, more aqua-fortis must be added, till the silver is all dissolved. If the operation has been performed slowly, the remaining gold will have the form of distinct masses. The gold appears black after parting; its parts have no adhesion together, because the silver dissolved from it has left many interstices. To give them more solidity, and improve their color, they are put into a test under a muffle, and made red-hot, after which they contract and become more solid, and the gold resumes its color and lustre. It is then called grain gold. If the operation has been performed hastily, the gold will have the appearance of black mud or powder, which, after well washing, must be melted.
The silver is usually recovered by precipitating it from the aqua-fortis by means of pure copper or by precipitation by muriatic acid and reduction. If the solution be perfectly saturated, no precipitation can take place till a few drops of aqua-fortis are added to the liquor. The precipitate of silver must be well washed with boiling water, and may be fused with nitre, or tested off with lead.
A cement is prepared, composed of 4 parts of bricks powdered and sifted; of 1 part of green vitriol calcined till it becomes red; and of 1 part of common salt. This is to be made into a firm paste with a little water. It is called the cement royal.
The gold to be cemented is reduced into plates as thin as money. At the bottom of the crucible or cementing pot, a stratum of cement, of the thickness of a finger, is put, which is covered with plates of gold; and so the strata are placed alternately. The whole is covered with a lid, which is luted with a mixture of clay and sand. This pot must be placed in a furnace or oven, heated gradually till it becomes red-hot, in which it must be continued during 24 hours. The heat must not melt the gold. The pot or crucible is then suffered to cool; and the gold carefully separated from the cement, and boiled at different times in a large quantity of pure water. It is then assayed upon a touch-stone, or otherwise; and if it be not sufficiently pure, it is cemented a second time. In this process the sulphuric acid of the calcined vitriol decomposes the common salt during the cementation, by uniting to its alkaline base, while the muriatic acid becomes concentrated by the heat and dissolves the silver alloyed with the gold.
This is a very troublesome process, though it succeeds when the portion of silver is so small that it would be defended from the action of aqua-fortis by the superabundant gold; but is little used, except to extract silver, or base metals, from the surface of gold, and thus giving to an alloyed metal the color and appearance of pure gold.
For separating silver from lead ores, enables us to reduce profitably ores containing but 1 oz. of silver to the ton. It depends upon the fact that an alloy of lead and silver when cooled, with occasional stirring, to near the point of solidification, crystallizes in part, and these crystals are found to contain much less lead than the original fused mass. Eight or ten cast-iron pots are arranged in line and heated. Into the centre one a charge, say 5 tons, of the original alloy is put; as the crystals form they are removed by means of a perforated ladle, and put in the pot to the right until about four-fifths have been removed; the remaining enriched lead is transferred to the pot to the left. This process is continued with the remaining pots, thus gradually enriching to the left and becoming poorer to the right. The rich alloy, termed lead riches, is then cupelled.
Metals, in general, will unite with each other by fusion or amalgamation, and acquire new properties. Brass is a compound of copper and zinc; and possesses a different color to either of the component parts.
As metals fuse in different degrees of heat, care should be taken not to add those metals which fuse easily, to others which require a greater degree of heat, while they are too hot, because the former may evaporate and leave the compound imperfect. Or, if they are brought into fusion together, it should be under a flux to prevent the volatile metals from evaporating before the union is effected.
Melt together equal parts of copper and zinc, at the lowest temperature that will fuse the former, stir them well to produce an intimate mixture of the metals, and add by degrees small quantities of zinc; the alloy first assumes a yellow color like brass; on adding a little more zinc it becomes purple, and lastly perfectly white, which is the proper appearance of the desired product when fused. The quantity of zinc to be used altogether, should be from 52 to 55 parts out of the hundred.
A beautiful gold-colored alloy, sold under the above name, gives on analysis: Copper, 86.4; zinc, 12.2; tin, 1.1; iron, 0.3. The presence of the iron was probably accidental.
Melt together 4 1/2 lbs. of tin, 1/2 lb. of bismuth, 1/2 lb. of antimony, and 1/2 lb. of lead. A very excellent alloy will be formed by using these proportions; it is used for making teapots and other vessels which are required to imitate silver. They retain their brilliancy to the last.
Another. - A very fine silver-looking metal is composed of 100 lbs. of tin, 8 of regulus of antimony, 1 of bismuth, and 4 of copper.
Melt together 16 lbs. of copper, 1 lb. of tin, and 1 lb. of zinc.
Put into a crucible 5 1/2 lbs. of copper; when fused, add 1/2 lb. of zinc; these metals will combine, forming an alloy of a reddish color, but possessing more lustre than copper, and also greater durability.
When copper is combined with arsenic, by melting them together in a close crucible, and covering the surface with common salt to prevent oxidation, a white brittle alloy is formed.
Melt in a crucible 7 lbs. of tin, and when fused throw in 1 lb. of lead, 6 oz. of copper and 2 oz. of zinc. This combination of metals will form an alloy of great durability and tenacity; also of considerable lustre.
The best sort of pewter consists of 100 parts of tin, and 17 of regulus of antimony.
Melt together 12 lbs. of tin, 1 lb. of regulus of antimony, and 4 oz. of copper.
Put into a crucible 2 lbs. of lead, and when melted throw in 1 lb. of tin. This alloy is that generally known by the name of solder. When heated by a hot iron and applied to tinned iron with powdered rosin, it acts as a cement or solder; it is also used to join leaden pipes, etc.
Melt together 2 lbs. of copper, and 1 lb of tin.
Melt together 2 lbs. of tin, and 1 of lead. The lining of tea chests makes a good solder for tin ware, being made of tin and lead in about the proper proportions.
Consists of 24 parts gold, 2 silver, and 1 of copper.
Hard - 4 parts of silver to 1 of copper. Soft - 2 parts of silver to 1 of brass wire.
Lead, 1000 parts; metallic arsenic, 3 parts.
Put into a crucible 10 lbs. of lead, and when it is in a state of fusion, throw in 2 lbs. of antimony; these metals, in such proportions, form the alloy of which common printing types are made. The antimony gives a hardness to the lead, without which the type would speedily be rendered useless in a printing press. Different proportions of lead, copper, brass, and antimony, frequently constitute this metal. Every artist has his own proportions, so that the same composition cannot be obtained from different foundries; each boasts of the superiority of his own mixture.
Melt 9 lbs. of lead, and throw into the crucible 2 lbs. of antimony and 1 lb. of bismuth; these metals will combine, forming an alloy of a peculiar quality. This quality is expansion as it cools; it is therefore well suited for the formation of small printing types (particularly when many are cast together to form stereotype plates), as the whole of the mould is accurately filled with the alloy; consequently there can be no blemish in the letters. If a metal or alloy liable to contract in cooling were to be used, the effect of course would be very different.
Another. - The proprietors of different foundries adopt different compositions for stereotype plates. Some form an alloy of 8 parts of lead, 2 parts of antimony, and 1/8 part of tin.
For the manufacture of stereotype plates, plaster of Paris, of the consistence of a batter-pudding before baking, is poured over the letter-press page, and worked into the interstices of the types with a brush. It is then collected from the sides by a slip of iron or wood, so as to be smooth and compact. In about 2 minutes the whole mass is hardened into a solid cake. This cake, which is to serve as the matrix of the stereotype plate, is now put upon a rack in an oven, where it undergoes great heat, so as to drive off superfluous moisture. When ready for use, these moulds, according to their size, are placed in flat cast-iron pots, and are covered over by another piece of cast-iron perforated at each end to admit the metallic composition intended for the preparation of the stereotype plates. The flat cast-iron pots are now fastened in a crane, which carries them steadily to the metallic bath, or melting pot where they are immersed and kept for a considerable time, until all the pores and crevices of the mould are completely and accurately filled. When this has taken place the pots are elevated from the bath by working the crane, and are placed over a water trough, to cool gradually. When cold the whole is turned out of the pots, and the plaster being separated by hammering and washing, the plates are ready for use; having received the most exact and perfect impression.
Melt together 10 oz. of lead, 5 oz. of bismuth, and 4 drs. of regulus of antimony.
Another. - Melt together 2 lbs. of regulus of antimony, 8 oz. of brass, and 10 oz. of tin.
Melt together 1 lb. of brass, 1 1/2 oz. of spelter, and 1/2 oz. of tin.
Melt together 2 parts of tin and 1 of bismuth.
Put into a crucible 4 oz. of bismuth, and when in a state of fusion throw in 2 1/2 oz. of lead, and 1 1/2 oz. of tin; these metals will combine, forming an alloy fusible at the temperature of boiling water. Mould this alloy in bars and take them to a silversmith's to be made into a half-adozen teaspoons. If one of these be given to a stranger to stir his tea as soon as it is poured from the teapot, he will be not a little surprised to find the spoon melt in the teacup.
The fusibility of this alloy is certainly surprising, for the fusing temperature of each of its components, singly, is higher than twice that of boiling water. Bismuth fuses at 476°, lead at 612, and tin at 442°; whilst water boils at 212°.
Another. - Melt together 1 oz. of zinc, 1 oz. of bismuth, and 1 oz. of lead. This alloy will be found to be remarkably fusible (although each of the metals, separately, requires considerable heat to melt it), and will melt even in hot water; it will likewise remain in a fused state on a sheet of paper, over the flame of a lamp or candle. Both of these alloys expand on cooling, and are well adapted for taking casts of medals, etc.
Melts between 150° and 160° Fahr. It consists of 3 parts cadmium, 4 tin, 8 lead, and 16 bismuth. It has a brilliant metallic lustre, and does not tarnish readily.
A combination of 3 parts of lead, with 2 of tin and 5 of bismuth, forms an alloy which melts at the temperature of 197° Fahr.
In making casts with this and similar alloys it is important to use the metal at a temperature as low as possible; as, if but a few degrees elevated, the water which adheres to the things from which casts are to be taken forms vapor, and produces bubbles. The fused metal must be allowed to cool in a teacup until just ready to set at the edges, and then pour it into the moulds, procuring in this way beautiful casts from moulds of wood, or of other similar substances. When taking impressions from gems, seals, etc. the fused alloy should be placed on paper or paste-board, and stirred about till it becomes pasty, from cooling, at which moment the gem, die, or seal should be suddenly stamped on it, and a very sharp impression will then be obtained.
Melt together equal parts of bismuth, lead, and tin, with a sufficient quantity of quicksilver.
This composition, with the addition of a small proportion of mercury, is used for injecting the vessels of many anatomical preparations; also for taking correct casts of various cavities of the body, as those of the ear. The animal structure may be corroded and separated by means of a solution of potassa in water, and the metallic cast will be preserved in an isolated state.
Melt together in a crucible 2 drs. of zinc and 1 of tin; when fused, pour them into a cold crucible containing 5 drs. of mercury. The mercury will combine with those metals and form an alloy (or amalgam, as it is called) fit to be rubbed on the cushions which press the plate or cylinder of an electrical machine. Before the amalgam is applied it is proper to rub the cushion with a mixture of tallow and beeswax.
Fuse 1/2 oz. of tin with the same quantity of bismuth in a crucible; when melted add 1/2 oz. of mercury. When perfectly combined take the mixture from the fire and cool it. This substance, mixed with the white of an egg, forms a very beautiful varnish for plaster figures, etc.
The plates are washed by an alkaline solution, then in water, heated, and sponged or sprinkled with the acid solution. The appearance varies with the degree of heat and the nature and strength of the acids employed. The plates, after the application of the acids, are plunged into water slightly acidulated, dried, and covered with white or colored varnishes. The following are some of the acid mixtures used: Nitro-muriatic acid, in different degrees of dilution; sulphuric acid, with 5 parts of water; 1 part of sulphuric acid, 2 of muriatic acid, and 8 of water; a strong solution of citric acid; 1 part nitric acid, 2 sulphuric, and 18 of water. Solution of potash is also used.
This art is erroneously termed silvering, for, as will be presently seen, there is not a particle of silver present in the whole composition.
On tin-foil, fitly disposed on a flat table, mercury is to be poured, and gently rubbed with a hare's-foot: it soon unites itself with the tin, which then becomes very splendid, or, as the workmen say, is quickened. A plate of glass is then cautiously to be slid upon the tin-leaf, in such a manner as to sweep off the redundant mercury which is not incorporated with the tin; leaden weights are then to be placed on the glass, and in a little time the quicksilvered tin foil adheres so firmly to the glass that the weights may be removed without any danger of its falling off. The glass thus coated is a common looking-glass. About 2 oz. of mercury are sufficient for covering 3 square feet of glass.
The success of this operation depends much on the clearness of the glass; and the least dirt or dust on its surface will prevent the adhesion of the amalgam or alloy.
Melt together 1 oz. of clean lead, and 1 oz. of fine tin, in a clean iron ladle; then immediately add 1 oz. of bismuth. Skim off the dross, remove the ladle from the fire. and before it sets add 10 oz. of quicksilver. Now stir the whole carefully together, taking care not to breathe over it, as the fumes of the mercury are very pernicious. Pour this through an earthen pipe into the glass globe, which turn repeatedly round.
Another. - To 4 oz. of quicksilver add as much tinfoil as will become barely fluid when mixed. Let the globe be clean and warm, and inject the quicksilver by means of a pipe at the aperture, turning it about till it is silvered all over. Let the remainder run out, and hang the globe up.
Another. - For this purpose 1 part of mercury and 4 of tin have been used; but if 2 parts of mercury, 1 of tin, 1 of lead, and 1 of bismuth are melted together, the compound which they form will answer the purpose better. Either of them must be made in an iron ladle, over a clear fire, and must be frequently stirred.
Prepare, 1. A solution of 10 grammes of nitrate of silver in 100 grammes of distilled water. 2. Take solution of ammonia of 13° Carter's areometer. 3. A solution of 20 grammes of pure caustic soda in 500 grammes of distilled water. 4. A solution of 25 grammes of ordinary white sugar in 200 grammes of distilled water. Pour into this 1 cubic centimetre of nitric acid, of 36°, and boil for 20 minutes; then make up the volume of 500 cubic centimetres with distilled water and 50 cubic centimetres of alcohol at 36°. This done, prepare an argentiferous solution, by mixing in a flask 12 cubic centimetres of solution 1, then 8 cubic centimetres of solution 2, then 20 centimetres of solution 3; and, lastly, make up a volume of 100 centimetres by 60 centimetres of distilled water. If the directions have been properly observed the liquid will remain limpid, and a drop of solution of nitrate of silver will produce a permanent precipitate. After being left quiet for 24 hours the solution is ready for use. Clean the surface to be silvered with a cotton plug moistened with a few drops of nitric acid; then wash with distilled water, drain, and place it on supports on the surface of a bath composed of the argentiferous liquid, to which has been added 1-10th or 1-12th of the solution of sugar (4). Under the influence of diffused light the liquid becomes yellow, then brown, and, after from 2 to 5 minutes, the whole surface of the glass will have been silvered. After 10 or 15 minutes it will have attained the required thickness. Wash first with ordinary water, then with distilled water; drain, dry, and polish with rouge on chamois. (A table of French Weights and Measures will be found at the end of the volume.)
Uncover and clean the damaged spot by very careful rubbing with fine cotton until there is no truce of grease or dust; then with the point of a knife cut the size of the required piece on the silvering of another glass; a small globule of mercury (the size of a pin's head for a surface the size of the finger nail) is dropped upon the cut piece. The mercury penetrates as far as the cut, and allows the piece to be removed. It is then gently pressed on the spot with a piece of cotton.
Melt together 1 lb. of brass and 4 1/2 oz. of speller.
Put 4 1/2 lbs. of copper into a crucible, expose it to heat in a furnace, and when perfectly fused add 1 1/2 lbs. of zinc. The metals will combine, forming that generally used alloy called brass.
Another. - For brass which is to be cast into plates, from which pans and kettles are to be made, and wire is to be drawn, braziers use calamine of the finest sort instead of pure zinc, and in a greater proportion than when common brass is made; generally 56 lbs. of calamine to 34 lbs. of copper. Old brass, which has frequently been exposed to the action of the fire, when mixed with the copper and calamine, renders the brass far more ductile and fitter for the making of fine wire than it would be without it.
Put into a crucible 5 oz. of pure copper; when it is in a state of fusion add 1 oz. of zinc. These metals combine, forming an alloy not unlike jeweller's gold; pour it into a mould of any shape. This alloy is used for inferior jewellery.
Some use only half this quantity of zinc, in which proportion the alloy is more easily worked, especially in the making of jewellery.
Another. - Melt together 1 oz. of brass with 1 1/2 or 2 oz. of copper, fused under a coat of charcoal-dust.
M. M. Mourier and Vallent, of Paris, have succeeded in making an alloy which imitates gold sufficiently near to merit the name Oreide. The properties are as follows: Pure copper, 100 parts, by weight; zinc, 17; magnesia, 6; sal ammoniac, 3.6; quicklime, 1.80; tarter of commerce, 9. The copper is first melted, then the magnesia, sal ammoniac, lime and tartar in powder, little by little; the crucible is briskly stirred for about 1/2 an hour, so as to mix thoroughly, and then the zinc is added in small grains by throwing it on the surface and stirring until it is entirely fused; the crucible is then covered and fusion maintained for about 35 minutes; the crucible is then uncovered, skimmed carefully, and the alloy cast in a mould of damp sand or metal. The oreide melts at a temperature low enough to allow its application to all kinds of ornamentation; it has a fine grain, is malleable, and capable of taking the most brilliant polish; when, after a time, it becomes tarnished from oxidation, its brilliancy may be restored by a little acidulated water. If the zinc is replaced by tin, the metal will be still more brilliant.
Melt together 3 oz. of copper, and 1 oz. of zinc; or, 8 oz. of brass and 1 oz. of zinc.
Another. - Melt in a crucible 4 oz. of copper, and when fused, add 2 oz. of zinc; they will combine, and form a very beautiful and useful alloy, called Prince Rupert's metal.
Melt in a clean crucible 7 lbs. of pure copper; when fused, throw into it 3 lbs. of zinc and 2 lbs. of tin. These metals will combine, forming bronze, which from the exactness of the impression which it takes from a mould, has, in ancient and modern times, been generally used in the formation of busts, medals and statues.
Melt 7 lbs. of copper, and when fused add 3 lbs. of zinc and 4 lbs. of tin. These metals will combine to form a beautiful alloy of great lustre, and of a light yellow color, fitted to be made into specula for telescopes. Mr. Mudge used only copper and grain tin, in the proportion of 2 lbs. to 14 1/2 oz.
Melt together 112 lbs. of Bristol brass, 14 lbs. of spelter, and 7 lbs. of block tin.
Another. - Melt together 9 parts of copper and 1 part of tin; the above compounds are those used in the manufacture of small and great brass guns, swivels, etc.
The pieces of ordnance used by the besiegers at the battle of Prague, were actually melted by the frequency of the firing; the mixture of which they were made contained a large portion of lead; it would have been less prone to melt, and consequently preferable, had it contained none. A mixture of copper and tin is preferred to pure copper, not only for the casting of cannon, but of statues, etc., for pure copper, in running through the various parts of the mold, would lose so much of its heat as to set, or become solid too soon.
Remarkable for great strength, being stronger than gunmetal or wrought-iron, consists of copper, 55.04; zinc, 42.36; tin, .83, iron, 1.77.
Resembles gold in appearance; is said to be twice as strong as the best gun-metal, as light as wrought-iron; is not easily tarnished. It is easily stamped and engraved. It is composed of 10 parts of aluminium and 90 of copper. It requires to be re-melted, as the first melting is brittle.
Mix together 24 parts of copper, 24 of tin and 8 of antimony. The tin, best quality of Bancoa, is to be added gradually to the melted composition.
Melt together 6 parts of copper and 2 of tin. These proportions are the most approved for bells throughout Europe and in China.
Another. - Some bells are made in the proportion of 10 parts of copper to 2 of tin. It may be in general observed, that a less proportion of tin is used for making church bells then clock bells, and that a little zinc is added for the bells of repeating watches and other small bells.
Melt together 8 oz. of copper and 1/2 oz. of neutral arsenical salt, fused together, under a flux composed of calcined borax, charcoal dust, and finely-powdered glass.
According to Pliny, the metal used by the Romans for their statues, and for the plates on which they engraved inscriptions, was composed in the following manner: They first melted a quantity of copper, into which they put a third of its weight of old copper, which had been long in use; to every 100 lbs. weight of this mixture they added 12 1/2 lbs. of an alloy composed of equal parts of lead and tin.
Can be rolled and worked at a red heat. It consists of 6 parts of copper and 4 of zinc.
Melt together 8 oz. of brass and 5 of spelter.
The principal object in fine casting is to have a mould that shall receive a beautiful impression, and at the same time sufficiently adhesive to resist the force of the fluid metal, that shall neither wash nor be injured by the heat. The sand that covers or surrounds the model should be fine, close sand; after removing the mould, the model must be faced with burnt rotten-stone, and covered with loam, each dusted through a bag, and the mould laid down upon it; this facing may be repeated, the mould must be dried and smoked with a torch; in lieu of water, the sand is moistened with a solution of tartar, or the lees of wine, or with cream of tartar. Care must be taken to loosen the band quickly, viz.: loosen the first mould while the second is pouring, etc. On removing the work, every particle of the facing should be carefully scraped from the mould and thrown away. Part the moulds with coal and black rosin.
Melt together 4 parts of copper, 1 of Bristol old brass and 14 oz. of tin to every lb. of copper.
Melt together 3 parts of copper, 1 of Bristol old brass and 4 oz. of tin to every lb. of copper.
If this alloy is for fine publishing, the tin maybe omitted, and a mixture of lead and antimony substituted. Paler polishing metal is made by reducing the copper to two or to one part.
Melt together 2 parts of brass, 1 part of copper, with a little old brass, and 1/4 oz. of tin to every lb. of copper. This alloy is almost of the color, etc., of gold coin.
Another. - Good dipping-metal may be made of 1 lb. of copper to 5 oz. of spelter; the copper should be tough cake, and not tile.
When antinomy is used instead of tin, it should be in smaller quantity, or the metal will be brittle.
When copper is melted with tin, about 3/4 oz. of tin to 1 lb. of copper, will make a pale bell metal; it will roll and ring very near to sterling silver.
Melt together 4 oz. of plate-brass and 4 oz. tin. When in fusion, add 4 oz. bismuth and 4 oz. regulus of antimony.
This is the hardening, which is to be added at discretion to melted tin, until it has the requisite color and hardness.
Another, - Melt together 2 lbs. of plate-brass, 2 lbs. of a mixture of copper and arsenic, either by cementing or melting, 2 lbs. of tin, 2 lbs. of bismuth and 2 lbs. regulus of antimony.
This is to be added at discretion to melted tin.
Another. - Melt together 1 lb. of copper, 1 lb. tin and 2 lbs. regulus of antimony, with or without a little bismuth.
Another. - Melt together 8 oz. Shruff brass, 2 lbs. regulus of antimony and 10 lbs. tin.
This is fit for use as Britannia metal.
Melt together 2 drs. of copper, 1 oz. of regulus of antimony and 12 oz. of tin.
To 8 oz. of scrap-iron or steel; at a white heat, add 1 lb. of antimony in small portions, with 3 oz. of nitre. Melt and harden 1 lb. of tin with 2 oz. of this compound.
Melt together 20 parts of copper, 15.8 of nickel.
Another. - Melt together 4 oz. of antimony, 1 oz. arsenic, and 2 lbs. tin. This compound is ready for use. The first of these Spanish alloys would be a beautiful metal, if arsenic were added.
Melt together 4 parts copper, 8 parts regulus of antimony, and 1 part bismuth.
When added to 100 parts of tin, this compound will be ready for use.
To 1 lb. of malleable iron, at a white heat, add 5 oz. regulus of antimony, and 24 lbs. of the purest Molucca tin.
This alloy polishes without the blue tint, and is free from lead or arsenic.
Take of fine silver, 19 dwts.; copper, 1 dwt.; and brass, 2 dwts. Melt these under a coat of charcoal-dust.
This solder possesses several advantages over the usual spelter solder, or brass, when employed in soldering cast-steel, etc., as it fuses with less heat, and its whiteness has a better appearance than brass.
Thin plates of brass are to be melted between the pieces that are to be joined. If the work be very fine, as when two leaves of a broken saw are to be brazed together, cover it with pulverized borax, melted with water, that it may incorporate with the brass powder which is added to it; the piece must be then exposed to the fire without touching the coals, and heated till the brass is seen to run.
Experiments have been made at Vienna, Dresden, and other places, in the use of tungsten or wolfram, in the alloying of steel, and some extraordinary results are stated to have been achieved. It is said that steel alloyed with 20 per cent. of tungsten produces a mixture, which, while it retains all the general qualities of steel, is so excessively hard, that tools made of it will cut, without difficulty, the hardest cast-steel.
M. De Ruolz and De Fontenay, of France, have lately obtained, after several years' experiments, a new alloy, which may be very useful for small coin and for many industrial uses. It is composed of 1/3 silver, 25 to 30 per cent. of nickel, and from 37 to 50 per cent. of copper. Its inventors propose to call it tiers-argent, or tri-silver. Its preparation is said to be a triumph of metallurgical science. The 3 metals when simply melted together form a compound which is not homogeneous; and to make the compound perfect, its inventors have been compelled to use phosphorus and certain solvents which they have not yet specified. The alloy thus obtained is at first very brittle; it cannot be hammered or drawn, and lacks those properties which are essential in malleable metals. But after the phosphorus is eliminated, the alloy perfectly resembles a simple metal, and possesses, in a very high degree, the qualities to which the precious metals owe their superiority. In color it resembles platinum, and is susceptible of a very high polish. It possesses extreme hardness and tenacity. It is ductile, malleable, very easily fused, emits when struck a beautiful sound, is not affected by exposure to the atmosphere, or to any but the most powerful reagents. It is without odor. Its specific gravity is a little less than that of silver. An alloy possessing these qualities must be very useful to gold and silversmiths, It can be supplied at a price 40 per cent. less than silver, and its greater hardness will give it a marked superiority. It may also serve as a substitute for goldplated or silver-plated articles, which are now so common on account of their cheapness, but which will not bear replating more than a few times, and which are, in the long run, sometimes more expensive than the pure metal. The new alloy, however, will be most useful for small coin. Its preparation and coinage are so difficult that the coin made of it cannot easily be counterfeited. Its hardness would render it more durable than silver; and thus the expense of re-coining, and the heavy loss arising from the wearing of our silver coinage, would be greatly diminished.
Silver coins, jewelry, or any other rich alloy, when moistened with a solution of chromic acid or a mixture of bichromate of potassa and sulphuric acid, become covered with a red purple spot of bichromate of silver. This spot does not occur on poor alloys or metals imitating silver.
Put into a clean crucible 7 1/2 drs. of pure gold and when perfectly melted, throw in 1/2 a dr. of platinum. The 2 metals will combine intimately forming an alloy rather whiter than pure gold, but remarkably ductile and elastic; it is also less perishable than pure gold or jeweller's gold; but more readily fusible than that metal.
These excellent qualities must render this alloy an object of great interest to workers in metals. For springs, where steel cannot be used, it will prove exceedingly advantageous.
It is a curious circumstance, that the alloy of gold and platinum is soluble in nitric acid, which does not act on either of the metals in a separate state. It is remarkable, too, that the alloy has very nearly the color of platinum, even when composed of 11 parts of gold to 1 of the former metal.
Melt together of Spanish copper, 6 dwts. and 12 grs.; fine silver, 3 dwts. and 16 grs.; to 1 oz. 5 dwts. of gold coin.
Melt together 8 oz. 8 dwts. of Spanish copper 10 dwts. of fine silver, to 1 oz. of gold coin.
Melt together 3 1/2 oz. of copper, 1 1/2 oz. of brass, and 15 grs. of pure gold.
Foils are thin plates or leaves of metal that are put under stones, or compositions in imitation of stones, when they are set.
The intention of foils is either to increase the lustre or play of the stones, or more generally to improve the color, by giving an additional force to the tinge, whether it be natural or artificial, by that of a ground of the same hue, which the foil is in this case made to be.
There are consequently two kinds of foils; the one is colorless, where the effect of giving lustre or play to the stone is produced by the polish of the surface, which makes it act as a mirror, and, by reflecting the light, prevents that deadness which attends the having a duller ground under the stone, and brings it by the double refraction of the light that is caused, nearer to the effect of the diamond. The other is colored with some pigment or stain of the same hue as the stone, or of some other which is intended to modify and change the hue of the stone in some degree; as, where a yellow foil may be put under green, which is too much inclined to the blue, or under crimson, where it is desired to have the appearance more orange or scarlet.
Foils may be made of copper or tin, and silver has been sometimes used, with which it has been advised, for some purposes, to mix gold; but the expense of either is needless, as copper may be made to answer the same end.
Where colored foils are wanted, copper may therefore be best used, and may be prepared for the purpose, by the following means:
Take copper plates beaten to a proper thickness, and pass them betwixt a pair of fine steel rollers very close set, and draw them as thin as is possible to retain a proper tenacity. Polish them with very fine whiting, or rottenstone, till they shine and have as much brightness as can be given them, and they will then be fit to receive the color.
Where the yellow, or rather orange-color of the ground would be injurious to the effect, as in the case of purples, or crimson red, the foils should be whitened, which may be done in the following manner:
Take a small quantity of silver and dissolve it in aqua-fortis, and then put bits of copper into the solution, and precipitate the silver; which being done the fluid must be poured off, and fresh water added to it, to wash away all the remainder of the first fluid; after which the silver must be dried, an equal weight of cream of tartar and common salt must then be ground with it, till the whole be reduced to a very fine powder, and with this mixture, the foils, being first slightly moistened, must be rubbed by the finger, or a bit of linen rag, till they be of the degree of whiteness desired; after which, if it appear to be wanted, the polish must be refreshed.
The tin foils are only used in the case of colorless stones, where quicksilver is employed; and they may be drawn out by the same rollers, but need not be further polished, as that effect is produced by other means in this case.
The manner of preparing foils, so as to give colorless stones the greatest degree of play and lustre, is by raising so high a polish or smoothness on the surface, as to give them the effect of a mirror which can only be done, in a perfect manner, by the use of quicksilver, applied in the same general way as in the case of looking-glasses. The method by which it may be best performed is as follows:
Take leaves of tin, prepared in the same manner as for silvering looking-glasses, and cut them into small pieces of such size as to cover the surface of the sockets or the stones that are to be set. Lay three of these then, one upon another, and having moistened the inside of the socket with thin gum-water, and suffered it to become again so dry that only a slight stickiness remains, put the three pieces of leaves, lying on each other into it, and adapt them to the surface in as even a manner as possible. When this is done, heat the socket and fill it with warm quicksilver, which must be suffered to continue in it 3 or 4 minutes, and then gently poured out. The stone must then be thrust into the socket, and closed with it, care having been taken to give such room for it that it may enter without stripping off the tin and quicksilver from any part of the furnace. The work should be well closed round the stone, to prevent the tin and quicksilver contained in the socket from being shaken out by any violence.
The lustre of stones set in this manner will continue longer than when they are set in the common way, as, the cavity round them being filled, there will be no passage found for moisture, which is so injurious to the wear of stones treated in any other way.
This kind of foil likewise gives some lustre to glass or other transparent matter, which has little of itself; but to stones or pastes that have some share of play it gives a most beautiful brilliance.
Two methods have been invented for coloring foils: the one by tingeing the surface of the copper of the color required by means of smoke, the other by staining or painting it with some pigment or other coloring substance.
The colors used for painting foils may be tempered with either oil, water rendered duly viscid by gum Arabic, size or varnish. Where deep colors are wanted, oil is most proper, because some pigments become wholly transparent in it, as lake, or Prussian blue; but yellow and green may be better laid on in varnish, as these colors may be had in perfection from a tinge wholly dissolved in spirit of wine, in the same manner as in the case of lacquers, and the most beautiful green is to be produced by distilled verdigris, which is apt to lose its color and turn black with oil. In common cases, however, any of the colors may be, with least trouble, laid on with isinglass size. in the same manner as the glazing colors used in miniature painting.
For red, where the ruby is to be imitated, carmine, a little lake used in isinglass size, or shellac varnish is to be employed, if the glass or paste be of a full crimson, verging towards the purple; but if the glass incline to the scarlet or orange, very bright lake (that is, not purple) may be used alone in oil.
For the garnet red, dragon's blood dissolved in seedlac varnish may be used; and for the vinegar garnet, the orange lake, tempered with shellac varnish, will be found excellent.
For the amethyst, lake, with a little Prussian blue, used with oil, and very thinly spread on the foil, will completely answer the end.
For blue, where a deep color, or the effect of the sapphire is wanted, Prussian blue, that is not too deep, should be used in oil, and it should be spread more or less thinly on the foil, according to the lightness or deepness of which the color is required to be.
For the eagle marine, common verdigris with a little Prussian blue, tempered in shellac varnish, may be used.
Where a full yellow is desired, the foil may be colored with yellow lacquer, laid on as for other purposes; and for the slighter color of topazes the burnish and foil itself will be sufficiently strong without any addition.
For green, where a deep hue is required, the crystals of verdigris, tempered in shellac varnish, should be used, but where the emerald is to be imitated, a little yellow lacquer should be added to bring the color to a truer green, and less verging to the blue.
The stones of more diluted color, such as the amethyst, topaz, vinegar-garnet and eagle-marine, may be very cheaply imitated by transparent white glass or paste, even without foils. This is to be done by tempering the colors above enumerated with turpentine and mastic, and painting the socket in which the counterfeit stone is to be set with the mixture, the socket and stone itself being previously heated. In this case, however, the stone should be immediately set, and the socket closed upon it before the mixture cools and grows hard. The orange lake above mentioned was invented for this purpose, in which it has a beautiful effect, and was used with great success by a considerable manufacturer. The color it produces is that of the vinegar-garnet, which it affords with great brightness. The colors before directed to be used in oil should be extremely well ground in oil of turpentine and tempered with old nut or poppy-oil; or, if time can be given for the drying, with strong fat oil diluted with spirit of turpentine, which will gain a fine polish of itself.
The colors used in varnish should be likewise thoroughly well ground and mixed; and, in the case of the dragon's blood in the seed-lac varnish and the lacquer, the foils should be warmed before they are laid out. All the mixtures should be laid on the foils with a broad, soft brush, which must be passed from one end to the other, and no part should be crossed or twice gone over, or, at least, not till the first coat can be dry; when, if the color do not lie strong enough, a second coat may be given.
Galvanoplasty or Electrotype, is the art of cold casting of metals by the agency of electricity. Its applications are extensive. It is used to multiply engravings and photographs; to cover the faces of types with harder metal; to deposit grad, silver, and alloys on other metals, etc. The process depends upon the fact that an electrical current passed through a metallic solution properly prepared, will cause a decomposition of the solution; the metal being deposited upon any conducting body attached to the negative pole (cathode) of a voltaic cell or battery. This is the pole attached to the zinc plate in all cases.
The term battery is properly applied to several voltaic cells united. Frequently, however, it is used to designate a single cell. The forms usually employed in practice are Smee's, Daniell's, and the nitric acid battery. In order to avoid confusion, the following points must be well understood. In all the batteries named, there are two plates and at exciting fluid. One of these plates is of zinc, which must be amalgamated by dipping it into weak sulphuric acid and rubbing the surface with mercury; or better still, immersing the whole plate in a bath of mercury. This must be repeated from time to time, when the battery is in use. This zinc plate is alone acted on by the exciting fluid. It is galled the positive plate. Attached to it is a binding screw, by which a wire may be connected with the plate. This screw, or the end of the attached wire, is called the pole or electrode. The name of the pole is opposite to that of the plate. The positive pole or anode being attached to the negative plate, and the negative pole or cathode to the positive (zinc) plate.
Usually the liquid to be decomposed (electrolyte) is kept in a separate vessel, and the current conveyed to it by wires. To the anode is usually attached a piece of metal of the same character as that to be deposited. This is gradually eaten away while the deposition is going on, on the cathode, and the solution thus kept of uniform strength. The current may be regulated by altering the distance between the poles. With the same battery power, the amount of electricity passing will be less as the distance of the poles in the electrolyte is greater. Too powerful a current must be avoided, as it renders the coating brittle and non-adherrent. It should not be strong enough to cause bubbles of gas to arise from the object. A large number of objects can be plated by one battery if they are suspended on copper rods, the ends of which are connected with the pole.
Consists of two plates of amalgamated zinc, separated by a piece of baked and varnished wood and between them a plate of silver having deposited on it by the electric current finely divided platinum; so as to roughen it and prevent the adhesion of hydrogen. The silver plate is fixed in the wood separating the zinc plates, to the zinc and to the silver plates are attached binding screws for the wires. The exciting fluid is dilute sulphuric acid; 1 part of acid to 20 of water, is strong enough. When more intensity is required several cells are joined by passing wires from the anode of one cell to the cathode of the next. This form of battery is generally preferred on account of its simplicity, constancy, and ease of management.
In delicate operations, as in copying engraved plates, where great constancy is required, this form of cell is employed. It consists of a plate of amalgamated zinc, one of copper, generally of cylindrical form separated by a cell of porous earthenware (a flower-pot with the hole closed by a cork, makes a very good porous cell). The plates and cell are enclosed in a glass or earthenware vessel; the zinc is excited by dilute sulphuric acid; the copper is kept immersed in saturated solution of sulphate of copper (blue-stone). The solution of copper is gradually decomposed; the copper being deposited in the copper plate. Hence there should always be a quantity of crystals of the sulphate at the bottom of the cell, and the solution should be stirred from time to time; or the crystals may be suspended in a basket near the top of the solution
When great intensity is required as in the deposition of copper on iron, and of certain alloys the decomposition of fused chlorides for the purpose of obtaining certain metals, these batteries are used. In all cases the positive plate is of amalgamated zinc excited by dilute sulphyric acid, which may be as strong as 1 in 10 with 1-10th of nitric acid. This is separated by a porous cell from the negative plate, which may be of platinum (Grove), carbon (Bunsen), or passive iron (Callan). The negative plate is immersed in strong nitric acid. Iron may be rendered passive by dipping it once or twice into strong nitric acid, and then washing with water and carefully drying.
Wash in weak lye to remove grease. Dip into dilute nitric acid to remove oxide. Scour with a hard brush and fine sand. Then having fastened to a wire, dip in strong nitric acid and immerse in the electrolyte as quickly as possible.
Add to a solution of nitrate of silver (made by dissolving silver in pure nitric acid), a solution of cyanide of potassium until no further precipitate is formed; but not enough to re-dissolve the precipitate already thrown down. Pour off the supernatant liquid, wash with water, and then redissolve the precipitate in cyanide of potassium. The anode should be of silver. Should the solution change on keeping, add a little fresh cyanide. Use a moderate current. An ounce and a half of silver will give to a surface a foot square, a coating as thick as common writing-paper. And since silver is worth $1.25 per ounce, the value of the silver covering a foot square, would be about $1.87. At this rate, a well plated tea-pot or coffeepot is plated at a cost in silver of not more than $1.50 to $2. The other expenses, including labor, would hardly be more than half that amount.
Add muriatic acid, carefully avoiding the fumes which are given off. Dilute the liquid, decant from the precipitate formed, dry the precipitate, and reduce in a black lead crucible with carbonate of soda.
Electro-gilding is done in like manner. The gold is dissolved in nitro-hydrochloric acid, washed with boiling nitric acid, and then digested with calcined magnesia. The gold is deposited in the form of an oxide, which after being washed in boiling nitric acid, is dissolved in cyanide of potassium, in which solution the articles to be plated with gold, after due preparation are placed. Iron, steel, lead, and some other metals that do not readily receive the gold deposit require to be first lightly plated with copper, or dipped in a solution of nitrate of silver, 1 part; nitrate of mercury, 1 part; nitric acid s.g. 1.384) 4 parts; water, 120 parts. The positive plate of the battery must be of gold, the other plate of iron or copper. The process is the same as that above described; use a feeble current.
The popular notion is, that genuine electro-gilding must necessarily add a good deal to the cost of the article plated. This is erroneous. A silver thimble may be so handsomely plated as to have the appearance of being all gold for 5 cents, a pencil-case for 20 cents, and a watch-case for 1 dollar. An estimate of the relative value of electrogilding, as compared with silver-plating, considering the cost of material alone, is about 15 to 1.
Dissolve 5 oz. powdered acetate of copper in 1/2 gall. of water; add 1 pt. of solution of ammonia; dissolve 10 oz. sulphate of zinc (white vitriol) in 1 gall. of water, at 180° Fahr., and when cool add 1 pt. of solution of ammonia. Dissolve 4 1/2 lbs. potassa in 1 gall. of water. Lastly, dissolve 8 oz. cyanide of potassium in 1 gall. of hot water. Mix in the following order: add the copper solution to that of zinc, then the potash and cyanide; digest for an hour or so, and add water to make up 8 gall. Work with a brass anode and an active battery power, occasionally adding more ammonia and cyanide.
Casts of the medals may be made in fusible metal, plaster, wax, etc. In case of a non-metallio mould it must have its face brushed over with black lead. The metallic mould is to be coated on the back with wax or varnish. The wire is usually attached to the edge by soldering or twisting. A decomposing cell is not necessary. A water-tight box is divided by a porous (plaster or leather) partition. On one side is a plate of zinc immersed in diluted, 1 to 20, sulphuric acid; on the other a solution, kept saturated, of sulphato of copper. A wire from the zinc is attached to a copper rod, from which the medals are suspended, dipping into the copper solution.
1. Brown. - Moisten the surface, well cleaned with weak nitric acid, allow it to dry, and apply a gentle heat.
2. Black. - Use, instead of nitric acid, sulphydrate of ammonia or liver of sulphur.
3. Green. - Expose in a close box to the fumes of chloride of lime, or to the vapor of acetic or muriatic acid.
4. For bronzing all sorts of fine copper or brass work a weak solution of bichloride of platinum is used. By varying the temperature and color, between a steel gray and deep black may be obtained
Prepare a solution of cyanide of copper, by dissolving oxide of copper in cyanide of potassium, or by adding cyanide of potassium to a solution of sulphate of copper, and redissolving the precipitate formed. Work with a strong battery power. The copper will not deposit unless the current be strong enough to evolve hydrogen at the cathode, which evolution should always be avoided in depositing the other metals.
When two metals are united and exposed to a corrosive agent, which would act unequally upon them if separate, the one which would be most acted on receives most of the force of the corrosion, while the other escapes. Thus iron coated with zinc (galvanized iron) will last for years exposed to the atmosphere. Copper points on lightning rods remain bright for a long time, when screwed into a zinc ball.
The following has been successfully employed in coating electrotype deposits with a coating of pure iron, thereby rendering them little inferior to steel-plate engravings as regards durability:-
Dissolve 1 lb. of sal ammoniac in 1 gall. of rainwater, then add 2 lbs. of neutral acetate of iron; boil the solution in an iron-kettle for 2 hours, replacing the water lost by evaporation; when cold, filter the solution, and keep it in close-covered vats (when not in use) to prevent oxidation.
The iron plate used in the decomposition-cell must be of the same surface as the plate to be coated with iron; a Smee's battery, of at least 3 cells, charged with 1 part sulphuric acid, and 60 parts water, being used for the decomposition.
To insure success the following rules must be observed: 1st. The plate must be thoroughly freed from any greasy matter by immersing in a solution of caustic soda, then rinsed in clean cold rainwater, after which dip it in dilute acetic acid, and immediately transfer it to the solution of iron; this will insure perfect adhesion between the metals. 2nd. The solution must be filtered previous to use to remove the oxide of iron formed by exposure to the atmosphere. After the plates have been coated with iron they must be well rinsed in clear warm rain-water, then in a weak alkaline solution, well dried with a piece of clean soft cotton, and slightly oiled to prevent oxidation.
The coating of iron is very hard and brittle, resembling the white iron used by manufacturers of malleable iron. Should any of the surface be damaged, the whole coating of iron may be removed by immersion in dilute sulphuric acid, and re-coated again by the above process.
Le Genie Industrial publishes the details of a process for making copper-tubes without soldering, which consists simply in depositing copper upon lead patterns by the galvanic battery, and then melting out the lead. It is said to work perfectly, and of course tubes could be made of any desired form - straight, curved, or right-angled. This suggests the idea of forming tubes in the same manner with cores of wax or clay. The clay may be forged into the size of the pipe through a draw-plate, then allowed to harden slightly, when it may be covered with plumbago and an electrodeposit of copper made upon it with a galvanic battery. When the copper is deposited in sufficient thickness the clay may be removed from the interior by boiling the pipe in water. To conduct this manufacture it would require long depositing-troughs, and the expense would probably be too great for making straight copper-tubes; but for curved tubes, such us the worms of stills, it would perhaps pay. Curved copper-tubes are commonly made by filling straight tubes with hot resin, then twisting the entire tube into its curved form. When the resin becomes cool it is driven out by striking the pipe, which breaks the resin-core into small pieces.
Drinking and other glasses are sometimes gilt on their edges. This is done, either by an adhesive varnish, or by heat. The varnish is prepared by dissolving in boiled linseedoil an equal weight either of copal or amber. This is to be diluted by a proper quantity of oil of turpentine, so as to be applied as thin as possible to the parts of the glass intended to be gilt. When this is done, which will be in about 24 hours, the glass is to be placed in a stove, till it is so warm as almost to burn the fingers when handled. At this temperature the varnish will become adhesive, and a piece of leaf gold, applied in the usual way, will immediately stick. Sweep off the superfluous portions of the leaf; and when quite cold it may be burnished, taking care to interpose a piece of very thin paper (Indian paper) between the gold And the burnisher. If the varnish is very good, this is the best method of gilding glass, as the gold is thus fixed on more evenly than in any other way.
It often happens, when the varnish is but indifferent, that by repeated washing the gold wears off; on this account the practice of burning it in is sometimes had recourse to.
For this purpose some gold powder is ground with borax, and in this state applied to the clean surface of the glass by a camel's-hair pencil. When quite dry the glass is put into a stove heated to about the temperature of an annealing oven; the gum burns off, and the borax, by vitrifying, cements the gold with great firmness to the glass, after which it may be burnished. The gilding upon porcelain is in like manner fixed by heat and the use of borax; and this kind of ware being neither transparent nor liable to soften, and thus to be injured in its form, in a low red heat, is free from the risk and injury which the finer and more fusible kinds of glass are apt to sustain from such treatment. Porcelain and other wares may be platinized, silvered, tinned, and bronzed in a similar manner.
This preparation, the invention of the brothers Dutuste, is reported on by Salvetat. The peculiar advantage of it is, that after burning the gold is so bright as not to require polishing. Thirty-two grammes of gold are gently warmed with 128 grammes of nitric acid and the same weight of hydrochloric acid. To the solution are added 12 grammes of tin and 1.2 grammes of butter of antimony, and, when all are dissolved, the solution is diluted with 500 grammes of water
A mixture is now prepared by heating together 80 grammes of oil of turpentine, 16 grammes of sulphur, and 16 grammes of Venice turpentine. When the sulphur is dissolved 50 grammes of oil of lavender is added. The gold solution is now added, and the two are well stirred together, until the aqueous solution becomes decolorized, showing that all the gold has united with the balsam. The watery portion is then poured away, and the oily fluid is washed with warm water, and then heated. When the last trace of moisture has disappeared 65 grammes more of lavender oil and 100 grammes of oil of turpentine are added, and the whole warmed to insure the perfect admixture. While quite fluid 5 grammes of subnitrate of bismuth are added. Afterwards the clear part is decanted from any reduced gold and other insoluble material and the balsam is concentrated to a fit consistence for painting with. The balsam so prepared is a thick fluid, of a pale-green color, the gold being perfectly dissolved. When proper care is taken to remove all moisture this preparation never blisters in burning.
In order to impress gilt figures, letters, and other marks upon leather, as on the covers of books, edgings for doors, etc., the leather must first be dusted over with very finely powdered yellow resin or mastic gum. The iron tools or stamps are now arranged on a rack before a clear fire, so as to be well heated, without becoming red hot. If the tools are letters, they have an alphabetical arrangement on the rack. Each letter or stamp must be tried, as to its heat, by imprinting its mark on the raw side of a piece of waste leather. A little practice will enable the workman to judge of the heat. The tool is now to be pressed downwards on the gold-leaf, which will of course be indented, and show the figure imprinted on it. The next letter or stamp is now to be taken and stamped in like manner, and so on with the others, taking care to keep the letters in an even line with each other, like those in a book. By this operation the resin is melted, consequently the gold adheres to the leather. The superfluous gold may then be rubbed off by a cloth, the gilded impressions remaining on the leather. In this, as in every other operation, adroitness is acquired by practice.
The cloth alluded to should be slightly greasy, to retain the gold wiped off (otherwise there will be great waste in a few months); the cloth will thus be soon completely saturated or loaded with the gold. When this is the case, these cloths are generally sold to the refiners, who burn them and recover the gold. Some of these afford so much gold by burning as to be worth from seven to ten dollars.
Letters written on velum or paper are gilded in 3 ways: in the first, a little size is mixed with the ink and the letters are written as usual; when they are dry, a slight degree of stickiness is produced by breathing on them, upon which the gold leaf is immediatley applied, and by a little pressure may be made to adhere with sufficient firmness. In the second method, some white-lead or chalk is ground up with strong size, and the letters are made with this by means of a brush; when the mixture is almost dry the gold leaf may be laid on, and afterwards burnished. The last method is to mix up some gold powder with size, and to form the letters of this by means of a brush. It is supposed that this latter method was that used by the monks in illuminating their missals, psalters, and rubrics.
The edges of the leaves of books and letter paper are gilded whilst in a horizontal position in the bookbinder's press, by first applying a composition formed of four parts of Armenian bole, and one of candied sugar, ground together with water to a proper consistence, and laid on by a brush, with the white of an egg. This coating, when nearly dry, is smoothed by the burnisher, which is generally a crooked piece of agate, very smooth, and fixed in a handle. It is then slightly moistened by a sponge dipped in clean water, and squeezed in the hand. The gold-leaf is now taken upon a piece of cotton from the leathern cushion and applied on the moistened surface. When dry it is to be burnished by rubbing the agate over it repeatedly from end to end, taking care not to wound the surface by the point of the burnisher. A piece of silk or India-paper is usually interposed between the gold and the burnisher
Cotton-wool is generally used by bookbinders to take the leaf up from the cushion, being the best adapted for the purpose on account of its pliability, smoothness, softness, and slight moistness.
Immerse a piece of white satin, silk, or ivory in a solution of chloride of gold, in the proportion of 1 part of the chloride to 3 of distilled water. Whilst the substance to be gilded is still wet, immerse it in a jar of hydrogen gas; it will soon be covered by a complete coat of gold.
The foregoing experiment may be very prettily and advantageously varied as follows: Paint flowers or other ornaments with a very fine camel-hair pencil, dipped in the above-mentioned solution of gold, on pieces of silk, satin, etc., and hold them over a Florence flask, from which hydrogen gas is evolved, during the decomposition of the water by sulphuric acid and iron filings. The painted flowers, etc., in a few minutes, will shine with all the splendor of the purest gold. A coating of this kind will not tarnish on exposure to the air or in washing.
The wood must first be covered or primed, by 2 or 3 coatings of boiled linseed-oil and carbonate of lead, in order to fill up the pores and conceal the irregularities of the surface occasioned by the veins in the wood. When the priming is quite dry a thin coat of gold size must be laid on. This is prepared by grinding together some red oxide of lead with the thickest drying oil that can be procured, and the older the better. That it may work freely, it is to be mixed, previously to being used, with a little oil of turpentine, till it is brought to a proper consistence. If the gold-size is good it will be sufficiently dry in 12 hours, more or less, to allow the artist to proceed to the last part of the process, which is the application of the gold. For this purpose a leaf of gold is spread on a cushion (formed by a few folds of flannel secured on a piece of wood, about 8 inches square, by a tight covering of leather), and is cut into strips of a proper size by a blunt pallet-knife; each strip, being then taken upon the point of a fine brush, is applied to the part intended to be gilded, and is then gently pressed down by a ball of soft cotton. The gold immediately adheres to the sticky surface of the size, and, after a few minutes, the dextrous application of a large camel's-hair brush sweeps away the loose particles of the gold-leaf without disturbing the rest. In a day or two the size will be completely dried, and the operation will be finished.
The advantages of this method of gilding are that it is very simple, very durable, and not readily injured by changes of weather, even when exposed to the open air, and when soiled it may be cleaned by a little warm water and a soft brush. Its chief employment is in out-door work. Its disadvantage is that it cannot be burnished, and therefore wants the high lustre produced by the following method:
This operation is chiefly performed on picture frames, mouldings, headings, and fine stucco-work. The surface to be gilt must be carefully covered with a strong size, made by boiling down pieces of white leather or clippings of parchment till they are reduced to a stiff jelly. This coating being dried, 8 or 10 more must be applied, consisting of the same size, mixed with fine Paris plaster or washed chalk. When a sufficient number of layers have been put on, varying according to the nature of the work, and the whole is become quite dry, a moderately thick layer must be applied, composed of size and Armenian bole, or yellow oxide of lead. While this last is yet moist the gold-leaf is to be put on in the usual manner. It will immediately adhere on being pressed by the cotton ball; and, before the size is become perfectly dry, those parts which are intended to be the most brilliant are to be carefully burnished by an agate or a dogs' tooth, fixed in a handle.
In order to save the labor of burnishing, it is a common, but bad practice, slightly to burnish the brilliant parts, and to deaden the rest by drawing a brush over them dipped in size; the required contrast between the polished and the unpolished gold is indeed thus obtained; but the general effect is much inferior to that produced in the regular way, and the smallest drop of water falling on the sized part occasions a stain. This kind of gilding can only be applied on in-door work, as rain, and even a considerable degree of dampness, will occasion the gold to peel off. When dirty it may be cleaned by a soft brush, with hot spirit of wine, or oil of turpentine.
The parts to be burnished (in gilding on metals) being covered with the usual guarding, the piece is fastened by five iron wires to the end of an iron rod; it is then to be highly heated until the guarding becomes brown, when the gilding will be found to have acquired a fine gold color. It is now to be covered with a mixture of common salt, nitre, and alum, liquefied in the water of crystallization they contain; the piece to be carried again to the fire and heated until the saline coating is in a state of fusion and becomes nearly transparent, when it must be withdrawn and suddenly plunged into cold water, which removes both coating and guarding. Dip it afterwards in very weak nitric acid, and wash it repeatedly in several separate tubs of water. It may be dried either by exposure to air, or gently wiping it with clean soft, dry linen.
Immerse a very clean bright piece of copper in a diluted solution of nitrate of mercury. By the affinity of copper for nitric acid, the mercury will be precipitated; now spread the amalgam of gold rather thinly over the coat of mercury just given to the copper. This coat unites with the amalgam, but of course will remain on the copper. Now place the piece or pieces so operated on in a clean oven or furnace, where there is no smoke. If the heat is a little greater than 660°, the mercury of the amalgam will be volatilized, and the copper will be beautifully gilt.
In the large way of gilding, the furnaces are so contrived that the volatilized mercury is again condensed and preserved for further use, so that there is no loss in the operation. There is also a contrivance by which the volatile particles of mercury are prevented from injuring the gilders.
Pour some of the ethereal solution of chloride of gold into a wineglass, and dip therein the blade of a new penknife, lancet, or razor; withdraw the instrument and allow the ether to evaporate. The blade will be found to be covered by a very beautiful coat of gold. A clean rag, or small piece of very dry sponge, may be dipped in the ether and used to moisten the blade with the same result.
In this case there is no occasion to pour the liquid into a glass, which must undoubtedly lose by evaporation; but the rag or sponge may be moistened by it by applying ether to the mouth of the phial. This coating of gold will remain on the steel for a great length of time, and will preserve it from rusting.
This is the way in which swords and other cutlery are ornamented. Lancets too are in this way gilded with great advantage to secure them from rust.
Gold powder may be prepared in three different ways: Put into an earthen mortar some gold-leaf with a little honey or thick gum-water, and grind the mixture till the gold is reduced to extremely minute particles. When this is done, a little warm water will wash out the honey or gum, leaving the gold behind in a pulverulent state.
Another. - Another way is, to dissolve pure gold (or the leaf) in nitro-muriatic acid, and then to precipitate it by a piece of copper or by a solution of sulphate of iron. The precipitate (if by copper, must be digested in distilled vinegar and then washed by pouring water over it repeatedly) and dried. This precipitate will be in the form of a very fine powder; it works better and is more easily burnished than gold-leaf ground with honey as above.
Another. - The best method of preparing gold powder is by heating a prepared amalgam of gold in an open clean crucible, and continuing the strong heat until the whole of the mercury is evaporated; at the same time constantly stirring the amalgam with a glass rod. When the mercury has completely left the gold, the remaining powder is to be ground in a Wedgwood mortar, with a little water, and afterwards dried. It is then fit for use.
Although the last mode of operating has been here given, the operator cannot be too much reminded of the danger attending the sublimation of mercury. In the small way here described, it is impossible to operate without danger; it is therefore better to prepare it according to the former directions, than to risk the health by the latter.
This method of gilding was invented by Mr. Turner of Birmingham. Mr. Turner first prepares ingots or pieces of copper or brass, in convenient lengths and sizes. He then cleans them from impurity, and makes their surfaces level, and prepares plates of pure gold, or gold mixed with a portion of alloy, of the same size as the ingots of metal, and of suitable thickness. Having placed a piece of gold upon an ingot intended to be plated, he hammers and compresses them both together so that they may have their surfaces as nearly equal to each other as possible; and then binds them together with wire, in order to keep them in the same position during the process required to attach them. Afterwards he takes silver-filings which he mixes with borax to assist the fusion of the silver. This mixture he lays upon the edge of the plate of gold, and next to the ingot of metal.
Having thus prepared the two bodies, he places them on a fire in a stove or furnace, where they remain until the silver and borax placed along the edges of the metals melt, and until the adhesion of the gold with the metal is perfect. He then takes the ingot carefully out of the stove. By this process the ingot is plated with gold, and prepared ready for rolling into sheets.
The principal difficulties in plating copper ingots are, to bring the surfaces of the copper and silver into fusion at the same time; and to prevent the copper from sealing; for which purposes fluxes are used. The surface of the copper on which the silver is to be fixed must be made flat by filing and should be left rough. The silver is first annealed, and afterwards pickled in weak muriatic acid: it is planished, and then scraped on the surface to be fitted on the copper. These prepared surfaces are anointed with a solution of borax, or strewed with fine powdered borax itself, and then confined in contact with each other, by binding wire. When they are exposed to a sufficient degree of heat, the flux causes the surfaces to fuse at the same time, and after they become cold they are found firmly united.
Copper may likewise be plated by heating it and burnishing leaf-silver upon it; so may iron and brass. This process is called French-plating.
Equal parts of sal-ammoniac and corrosive sublimate, are dissolved in spirit of nitre, and a solution of gold made with this menstruum. The silver is brushed over with it, which is turned black, but on exposure to a red heat, it assumes the color of gold.
Take an aqua regia, composed of 2 parts of nitric acid and 1 of muriatic acid; let the gold be granulated, put into a sufficient quantity of this menstruum, and exposed to a moderate degree of heat. During the solution an effervescence takes place, and it acquires a beautiful yellow color which becomes more and more intense, till it has a golden or even orange color. When the menstruum is saturated, it is very clear and transparent.
Fine linen rags are soaked in a saturated solution of gold in aqua regia, gently dried, and afterwards burnt to tinder. The substance to be gilt must be well polished, a piece of cork is first dipped into a solution of common salt in water, and afterwards into the tinder, which is well rubbed on the surface of the metal to be gilt, and the gold appears in all its metallic lustre.
A quantity of quicksilver is put into a crucible or iron ladle, which is lined with clay and exposed to heat till it begins to smoke. The gold to be mixed should be previously granulated, and heated red hot, when it should be added to the quicksilver, and stirred about with an iron rod till it is perfectly dissolved. If there should be any superfluous mercury, it may be separated by passing it through clean soft leather, and the remaining amalgam will have the consistence of butter, and contain about 3 parts of mercury to 1 of gold.
The metal to be gilt is previously well cleaned on its surface, by boiling it in a weak pickle, which is a very dilute nitrous acid. A quantity of aqua-fortis is poured into an earthen vessel, and quicksilver put therein; when a sufficient quantity of mercury is dissolved, the articles to be gilt are put into the solution, and stirred about with a brush till they become white. This is called quickening. But, as during quicking by this mode, a noxious vapor continually arises, which proves very injurious to the health of the workman, they have adopted another method, by which they, in a great measure, avoid that danger. They now dissolve the quicksilver in a bottle containing aqua-fortis, and leave it in the open air during the solution, so that the noxious vapor escapes into the air. Then a little of this solution is poured into a basin, and with a brush dipped therein they stroke over the surface of the metal to be gilt, which immediately becomes quicked. The amalgum is now applied by one of the following methods, viz:
1st. By proportioning it to the quantity of articles to be gilt, and putting them into a white hat together, working them about with a soft brush till the amalgam is uniformly spread.
Or, 2dly. By applying a portion of the amalgam upon one part, and spreading it on the surface, if flat, by working it about with a harder brush.
The work thus managed is put into a pan, and exposed to a gentle degree of heat; when it becomes hot, it is frequently put into a hat, and worked about with a painter's large brush, to prevent an irregular dissipation of the mercury, till at last the quicksilver is entirely dissipated by a repetition of the heat, and the gold is attached to the surface of the metal. This gilt surface is well cleaned by a wire brush, and then artists heighten the color of the gold by the application of various compositions, this part of the process is called coloring.
For silvering copper, covering the worn parts of plated goods, etc.
1. Nitrate of silver, common salt, each 30 grs.; cream of tartar, 3 1/2 drs. Mix. Moisten with cold water and rub on the article to be silvered.
2. Pure silver (precipitated from the nitrate by copper), 20 grs.; alum 30 grs.; cream of tartar, 2 drs.; salt, 2 drs.
3. Precipitated silver, 1/2 oz.; common salt, sal ammoniac, each 2 oz.; corrosive sublimate, 1 dr. Make into a paste with water. Copper utensils are previously boiled with cream of tartar and alum, rubbed with this paste made red hot and afterwards polished.
4. Nitrate of silver, 1 part; cyanide of potassium, 3 parts; water enough to make a paste.
Among the many branches of manufacturing at Nuremberg, in Germany, that of metals into various articles has obtained considerable importance. They include silver-plated ware of different styles and quality; which necessarily produce large quantities of spoiled materials and clippings, the recovery of which has hitherto been very imperfectly accomplished; thus causing annually a considerable loss. The reason of it was, the want of a method by which the silver might be removed without much expense, and the copper thus forged from its coating used again.
Repeted experiments have led to a very simple process, by the action of concentrated nitric acid on silver and copper when present together. If these metals are placed into common commercial acid, (sp. gr. 1.47) they will both be strongly acted on; but a separation of the two is unattainable, since the copper, so long as any remains undissolved, will precipitate the silver from its solution by galvanic action. Nitric acid of the highest specific gravity (1.5), however, acts on the silver, but not on the copper: it renders the copper more electro-negative than before, less oxidizable, and deprives it of the property of decomposing the acid, and precipitating the silver.
To produce this passive condition of copper, it is not absolutely necessary to employ directly acid of that specific gravity; for any concentrated nitric acid can be made to answer the purpose by the addition of a sufficient quantity of the oil of vitriol, which deprives it of a portion of its water and thus contributes to make it stronger. A mixture of one volume of nitric acid (sp. gr. 1.47) and six of vitriol does not dissolve copper at the temperature of boiling water; but with a smaller proportion of sulphuric acid, evolution of nitrous acid takes place. The same end and much cheaper, is obtained by employing a mixture of oil of vitriol and nitrate of soda, which are the materials used in the practice. The following is the method now generally employed: Oil of vitriol, together with five per cent. of nitrate of soda, is heated in a cast-iron boiler; or better, a stoneware pan, to 212° Fahr. The silver-plated clippings are placed in a sheetiron bucket or colander, which is fastened to a pulley that may be moved about in the acid. As soon as the silver is removed, the colander is raised, allowed to drain, then immersed in cold water and emptied, to be again used in the same manner. When the acid-bath is fresh, the desilvering proceeds very rapidly, and even with heavy plated ware takes but a few minutes; with the gradual saturation of the bath more time is required, and it is readily perceived when the acid must be renewed. The small amount of acid solution adhering to the copper, precipitates its silver when brought into the water. To obtain its complete removal, the clippings, when raised from the desilvering bath and before immersion in water, may be dipped into a second bath prepared in the same manner, which is afterwards to be used in place of the first.
The saturated bath, on cooling, congeals to a crystalline semi-fluid mass of sulphate of copper and of soda. The silver is removed by chloride of sodium, which is added in small portions at a time, while the solution is yet warm. The chloride of silver separates readily, and is washed and reduced in the usual manner. The acid solution contains but a very small portion of copper, hardly enough to pay for recovering.
This process is applied to recover the silver from the plated metal, which has been rolled down for buttons, toys, etc., without destroying any large portion of the copper. For this purpose, a menstruum is composed of 3 lbs. of oil of vitriol, 1 1/2 oz. of nitre, and 1 lb. of water. The plated metal is boiled in it till the silver is dissolved, and then the silver is recovered by throwing common salt into the solution.
Iron may be plated by three different modes.
1. By polishing the surface very clean and level with a burnisher, and afterwards by exposing it to a blueing heat, a leaf of silver is properly placed and carefully burnished down. This is repeated till a sufficient number of leaves are applied, to give the silver a proper body.
2. By the use of a solder; slips of thin solder are placed between the iron and silver, with a little flux, and secured together by binding wire. It is then placed in a clear fire, and continued in it till the solder melts, when it is taken out, and on cooling is found to adhere firmly.
3. By tinning the iron first, and uniting the silver by the intermedia of slips of rolled tin, brought into fusion in a gentle heat.
Take of saltpetre, 6 oz.; green copperas, 2 oz.; white vitriol and alum, of each, 1 oz.
If it be wanted redder, a small portion of blue vitriol must be added. These are to be well mixed, and dissolved in water as the color is wanted.
Take of saltpetre, 1 oz. 10 dwts.: sal ammoniac, 1 oz. 4 dwts.; Roman vitriol, 1 oz. 4 dwts.; verdigris, 18 dwts. Mix them well together and dissolve a portion in water, as occasion requires.
The work must be dipped in these compositions, applied to a proper heat to burn them off, and then quenched in water or vinegar.
To 4 oz. of melted yellow wax, add, in fine powder, 1 1/2 oz. of red ochre, 1 1/2 oz. of verdigris, calcined till it yield no fumes, and 1/2 oz. of calcined borax; mix them well together. It is necessary to calcine the verdigris, or else by the heat applied in burning the wax, the vinegar becomes so concentrated as to corrode the surface, and make it appear speckled.
Apply a solution of borax, in water, to the gilt surface, with a fine brush, and sprinkle over it some fine powdered sulphur. Make the piece red-hot and quench it in water. The gold may be easily wiped off with a scratch-brush, and recovered by cupellation.
Gold is taken from the surface of silver by spreading over it a paste made of powdered sal ammoniac, with aquafortis, and heating it till the matter smokes, and is nearly dry, when the gold may be separated by rubbing it with a scratch-brush.
Boil 6 lbs. of cream of tartar, 4 galls. of water, and 8 lbs. of grain-tin, or tin shavings. After the materials have boiled a sufficient time, the substance to be tinned is put therein and the boiling continued, when the tin is precipitated in its metallic form.
Iron which is to be tinned is first steeped in acid materials, such as sour whey, distillers' wash, etc., then scoured and dipped in melted tin, having been first rubbed over with a solution of sal ammoniac. The surface of the tin is prevented from calcining by covering it with a coat of fat. Copper vessels must be well cleansed, and then a sufficient quantity of tin with sal ammoniac is put therein and brought into fusion, and the copper vessel moved about. A little resin is sometimes added. The sal ammoniac prevents the copper from scaling, and causes the tin to be fixed wherever it touches.
Put 1/2 oz. of the sugar of lead, in powder, into a clear glass globe or wine decanter, filled to the bottom of the neck with distilled water and 10 drops of nitric acid, and shake the mixture well.
Prepare a rod of zinc with a hammer and file, so that it may be a quarter of an inch thick and 1 inch long, at the same time form notches in each side for a thread, by which it is to be suspended, and tie the thread so that the knot shall be uppermost when the metal hangs quite perpendicular. When it is tied, pass the two ends of the thread through a perforation in the cork, and let them be again tied over a small splinter of wood which may pass between them and the cork. When the string is tied, let the length between the cork and the zinc be such that the precipitant (the zinc) may be at equal distances from the sides, bottom and top of the vessel, when immersed in it. When all things are thus prepared, place the vessel in a place where it may not be disturbed and introduce the zinc, at the same time fitting in the cork. The metal will very soon be covered with the lead, which it precipitates from the solution, and this will continue to take place until the whole be precipitated upon the zinc, which will assume the form of a tree or bush, the leaves and branches of which are laminal, or plates of a metallic lustre.
Into the same, or a similar vessel to that used in the last experiment, pour distilled water as before, and put in 3 drs. of chloride of tin, adding 10 drops of nitric acid, and shake the vessel until the salt is completely dissolved. Replace the zinc (which must be cleared from the effects of the former experiment) as before, and set the whole aside to precipitate without disturbance. In a few hours the effect will be similar to the last, only that the tree of tin will have more lustre.
Pour into a glass globe or decanter 4 drs. of nitrate of silver dissolved in a lb. or more of distilled water, and lay the vessel on the chimney piece, or in some place where it may not be disturbed. Now pour in 4 drs. of mercury. In a short time the silver will be precipitated in the most beautiful arborescent form, resembling real vegetation. This has been termed the Arbor Diana
The operation is carried on by two men; one is seated on the floor with a large flat stone before him, and with a movable flat stone-stand at his side. His fellow-workman stands beside him with a crucible filled with melted lead, and having poured a certain quantity upon the stone, the other lifts the movable stone, and dashing it on the fluid lead presses it out into a flat and thin plate, which he instantly removes from the stone. A second quantity of lead is poured in a similar way, and a similar plate formed, the process being carried on with singular rapidity. The rough edges of the plates are then cut off, and they are soldered together for use.
The way of proceeding is by stamping, washing, etc., the calcine and materials, to seperate the ore from extraneous matter; then fusing the prepared ore in an open furnace, and instead of casting it, to suffer it to remain at the bottom of the furnace till it becomes cold.
The ore being fused in a reverberating furnace, is conveyed, while fluid, into an air-furnace, where it is exposed to a strong heat till a bluish flame is observed on the surface, it is then agitated on the surface till it loses its fusibility and is collected into lumps galled loops. These loops are then put into another air-furnace, brought to a white or welding heat, and then shingled into half-blooms or slabes. They are again exposed to the air-furnace, and the half-blooms taken out and forged into anconies, bars, halfflats, and rods for wire; while the slabes are passed, when of a welding heat, through the grooved rollers. In this way of proceeding, it matters not whether the iron is prepared from cold or hot short metal, nor is there any occasion for the use of finery, charcoal, coke, chafery or hollow-fire; or any blast by bellows or otherwise, or the use of fluxes in any part of the process.
This consists in the skilful bundling of the iron to be welded, in the use of an extraordinarily large forgehammer, in employing a bulling-furnace, instead of a hollowfire or chafery, and in passing the iron, reduced to a melting heat, through grooved mill rollers of different shapes and sizes, as required.
Melt borax in an earthen vessel, and add 1-10th of pounded sal ammoniac. When well mixed, pour it out on an iron plate, and as soon as it is cold, pulverize and mix it with an equal quantity of unslaked lime. To proceed to the operation, the iron or steel must be first heated to a red heat, and the powder strewed over it; the pieces of metal thus prepared are to be again put in the fire, and raised to a heat considerably;ower than the usual welding one, when it is to be withdrawn and well beaten by a hammer till the surfaces are perfectly united.
Soft metals can be welded cold by great pressure and recently hydraulic pressure has been applied by M. Duportail to the welding of heated masses of iron. The advantage of pressure over hammering, is that it reaches the centre of the bar and produces a homogeneous weld.
Iron by being heated red-hot, and plunged into cold water, acquires a great degree of hardness. This proceeds from the coldness of the water which contracts the particles of the iron into less space.
Case-hardening is a superficial conversion of iron into steel by cementation. It is performed on small pieces of iron by enclosing them in an iron box containing burnt leather, bone-dust, or ferrocyanide of potassium, and exposing them for some hours to a red heat. The surface of the iron thus becomes perfectly hardened. Iron thus treated is susceptible of the finest polish.
The iron is formed into bars of a convenient size, and then placed in a cementing furnace with a sufficient quantity of cement, which is composed of coals of animal or vegetable substances, mixed with calcined bones, etc. The following are excellent cements: 1st, 1 part of powdered charcoal and 1/2 a part of wood-ashes well mixed together; or, 2nd, 2 parts of charcoal, moderately powdered, 1 part of borax, horn, hair, or skins of animals, burnt in close vessels to blackness, and powdered, and 1/2 a part of wood-ashes; mix them well together. The bars of iron converted into steel, are placed upon a stratum of cement, and covered all over with the same, and the vessel which contains them, closely luted, must be exposed to a red heat for 8 or 10 hours, when the iron will be converted into steel.
Steel is prepared from bar-iron by fusion; which consists of plunging a bar into melted iron, and keeping it there for some time, by which process it is converted into good steel.
All iron which becomes harder by suddenly quenching in cold water is called steel; and that steel which in quenching acquires the greatest degree of hardness in the lowest degree of heat, and retains the greatest strength in and after induration, ought to be considered as the best.
Articles manufactured of steel for the purposes of cutting, are, almost without an exception, hardened from the anvil; in other words, they are taken from the forger to the hardener without undergoing any intermediate process; and such is the accustomed routine, that the mischief arising has escaped observation. The act of forging produces a strong scale or coating, which is spread over the whole of the blade; and to make the evil still more formidable, this scale or coating is unequal in substance, varying in proportion to the degree of heat communicated to the steel in forging: it is, partially, almost impenetrable to the action of water when immersed for the purpose of hardening. Hence it is that different degrees of hardness prevail in nearly every razor manufactured; this is evidently a positive defect, and so long as it continues to exist, great difference of temperature must exist likewise. Razor-blades not unfrequently exhibit the fact here stated in a very striking manner; what are termed clouds, or parts of unequal polish, derive their origin from this cause; and clearly and distinctly, or rather distinctly though not clearly, show how far this partial coating has extended, and where the action of the water has been yielded to, and where resisted. It certainly cannot be matter of astonishment, that so few improvements hove been made in the hardening of steel, when the evil here complained of so universally obtains, as almost to warrant the supposition that no attempt has ever been made to remove it. The remedy, however, is easy and simple in the extreme, and so evidently efficient in its application, that it cannot but excite surprise, that, in the present highly improved state of our manufactures, such a communication should be made as a discovery entirely new.
Instead, therefore, of the customary mode of hardening the blade from the anvil, let it be passed immediately from the hands of the forger to the grinder; a slight application of the stone will remove the whole of the scale or coating, and the razor will then be properly prepared to undergo the operation of hardening with advantage. It will be easily ascertained, that steel in this state heats in the fire with greater regularity, and that when immersed, the obstacles being removed to the immediate action of the water on the body of the steel, the latter becomes equally hard from one extremity to the other. To this may be added that, as the lowest possible heat at which steel becomes hard is indubitably the best, the mode here recommended will be found the only one by which the process of hardening can be effected with a less portion of fire than is, or can be, required in any other way. These observations are decisive, and will, in all probability, tend to establish in general use, what cannot but be regarded as a very important improvement in the manufacturing of edged steel instruments. Rhodes' Essay on the Manufacture of a Razor.
Gravers, axes, and in fact all steel instruments that require to be excessively hard, may be easily rendered so by heating them to the tempering degree and hammering them till cold. If a graver, it is to be heated to a straw-color, hammered on the acute edge of the belly, tempered to the straw color again, ground and whetted to a proper shape. A graver thus prepared will cut into steel, without previous decarbonization. If the point should on trim be found not sufficiently hard, the operation of heating, hammering, and tempering, etc., may be repeated as often as necessary.
The finest of steel, called English cast-steel, is prepared by breaking to pieces blistered steel, and then melting it in a crucible with a flux composed of carbonaceous and vitrifiable ingredients. The vitrifiable ingredient is used only inasmuch as it is a fusible body, which flows over the surface of the metal in the crucibles, and prevents the access of the oxygen of the atmosphere. Broken glass is sometimes used for this purpose.
When thoroughly fused it is cast into ingots, which. by gentle heating and careful hammering, are tilted into bars. By this process the steel becomes more highly carbonized in proportion to the quantity of flux, and in consequence is more brittle and fusible than before. Hence it surpasses all other steel in uniformity of texture, hardness, and closeness of grain, and is the material employed in all the finest articles of English cutlery.
This method consists in fixing a clean piece of wrought iron, brought to a welding-heat, in the centre of a mould, and then pouring in melted steel, so as entirely to envelop the iron; and then forging the mass into the shape required.
The steel must be finely polished on its surface, and then exposed to a uniform degree of heat. Accordingly, there are three ways of coloring: first, by a flame producing no soot, as spirit of wine; secondly, by a hot plate of iron; and thirdly, by wood-ashes. As a very regular degree of heat is necessary, wood-ashes for fine work bears the preference. The work must be covered over with them, and carefully watched; when the color is sufficiently heightened, the work is perfect. This color is occasionally taken off with a very dilute muriatic acid.
The principal characters by which steel may be distinguished from iron, are as follows:-
1. After being polished, steel appears of a whiter light gray hue, without the blue cast exhibited by iron. It also takes a higher polish.
2. The hardest steel, when not annealed, appears granulated, but dull, and without shining fibres.
3. When steeped in acids the harder the steel is, of a darker hue is its surface.
4. Steel is not so much inclined to rust as iron.
5. In general, steel has a greater specific gravity.
6. By being hardened and wrought, it may be rendered much more elastic than iron,
7. It is not attracted so strongly by the magnet as soft iron. It likewise acquires magnetic properties more slowly, but retains them longer; for which reason, steel is used in making needles for compasses and artificial magnets.
8. Steel is ignited sooner, and fuses with less degree of heat than malleable iron, which can scarcely be made to fuse without the addition of powdered charcoal; by which it is converted into steel, and afterwards into crude iron.
9. Polished steel is sooner tinged by heat, and that with higher colors than iron.
10. In a calcining heat, it suffers less loss by burning than soft iron does in the same heat, and the same time. In calcination a light blue flame hovers over the steel, either with or without a sulphurous odor.
11. The scales of steel are harder and sharper than those of iron and consequently more fit for polishing with.
12. In a white heat, when exposed to the blast of the bellows among the coals, it begins to sweat wet, or melt, partly with light-colored and bright and partly with red sparkles, but less crackling than those of iron. In a melting heat, too, it consumes faster.
13. In the sulphuric, nitric, and other acids steel is violently attacked, but is longer in dissolving than iron. After maceration, according as it is softer or harder, it appears of a lighter or darker gray color; while iron on the other hand is white.
Hematite pig-iron smelted with coke and hot-blast has chiefly been used. The metal is melted in a reverberatory furnace, and is then run into a founder's ladle, and from thence it is transferred to the vessel in which its conversion into steel is to be effected. It is made of stout plate iron and lined with a powdered argillaceous stone found in this neighborhood below the coal, and known as ganister. The converting vessel is mounted on axes, which rest on stout iron standards, and by means of a wheel and handle it may be turned into any required position. There is an opening at the top for the inlet and pouring out of the metal, and at the lowest part are inserted 7 fire-clay tuyeres, each having five openings in them; these openings communicate at one end with the interior of the vessel, and at the other end with a box called the tuyere-box, into which a current of air from a suitable blast engine is conveyed under a pressure of about 14 lbs. to the square inch, a pressure more than sufficient to prevent the fluid metal from entering the tuyeres. Before commencing the first operation, the interior of the vessel is heated by coke, a blast through the tuyeres being used to urge the fire. When sufficiently heated, the vessel is turned upside down and all the unburned coke is shaken out. The molten pig-iron is then run in from the ladle before referred to; the vessel, during the pouring in of the iron, is kept in such a position that the orifices of the tuyeres are at a higher level than the surface of the metal. When all the iron has run in the blast is turned on, and the vessel quickly moved round. The air then rushes upwards into fluid metal from each of the 35 small orifices of the tuyeres, producing a most violent agitation of the whole mass. The silicium, always present in greater or less quantities in pig-iron, is first attacked. It unites readily with the oxygen of the air, producing silicic acid; at the same time a small portion of the iron undergoes oxidation, hence a fluid silicate of the oxide of iron is formed, a little carbon being simultaneously eliminated. The heat is thus gradually increased until nearly the whole of the silicium is oxidized; this generally takes place in about 12 minutes from the commencement of the process. The carbon now begins to unite more freely with the oxygen of the air, producing at first a small flame, which rapidly increases, and in about three minutes from its first appearance we have a most intense combustion going on: the metal rises higher and higher in the vessel, sometimes occupying more than double its former space. The frothy liquid now presents an enormous surface to the action of the oxygen of the air, which unites rapidly with the carbon contained in the crude iron, and produces a most intense combustion, the whole, in fact, being a perfect mixture of metal and fire. The carbon is now eliminated so rapidly as to produce a series of harmless explosions, throwing out the fluid slags in great quantities while the union of the gases is so perfect that a voluminous white flame rushes from the mouth of the vessel, illuminating the whole building, and indicating to the practiced eye the precise condition of the metal inside. The workman may thus leave off whenever the number of minutes he has been blowing and the appearance of the flame indicate the required quality of the metal. This is the mode preferred in working the process in Sweden. But here we prefer to blow the metal until the flame suddenly stops, which it does just on the approach of the metal to the condition of malleable iron: a small quantity of charcoal pigiron, containing a known quantity of carbon, is then added, and steel is produced of any desired degree of carburation, the process having occupied about 28 minutes from the commencement. The vessel is then turned, and the fluid steel is run into the casting ladle, which is provided with a plug rod covered with loam: the rod posses over the top of the ladle, and works in guides on the outside of it, so that, by means of a lever handle, the workmen may move it up and down as desired. The lower part of the plug, which occupies the interior of the ladle, has fitted to its lower end a fireclay cone, which rests in a seating of the same material let into the bottom of the ladle, thus forming a cone valve, by means of which the fluid steel is run into different-sized moulds, as may be required, the stream of fluid steel being prevented by the valve plug from flowing during the movement of the casting ladle from one mould to another. By tapping the metal from below, no scoria or other extraneous floating matters are allowed to pass into the mould.
Pig iron is first granulated by running it in a small stream into cold water kept constantly agitated. The granulated metal is mixed with sparry iron ore, and if necessary a small portion of manganese, and heated in crucibles in the ordinary cast-steel blast furnace.
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