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To Prepare a Solution of Gold

Dissolve 4 troy ounces cyanide of potassium and 1 ounce cyanide of gold in 1 gallon rain or distilled water. This solution is to be used at about 90° Fahr., with a battery of at least two cells. Gold can be deposited, of various shades to suit the taste, by adding to the gold solution a small quantity of the cyanides of gilding solution. silver, copper, or zinc, and a few drops of 3732. Conditions Required in Electrohydrosulphuret of ammonia. Gilding. The gilding solution generally 3729. Το Prepare a Gold Solution contains from one-half to an ounce of gold in by the Battery Process. To prepare a the gallon, but for covering small articles, gallon of gold solution, dissolve 4 ounces such as medals, for tinging daguerreotypes, cyanide of potassium in 1 gallon water, and gilding rings, thimbles, etc., a weaker solution heat the solution to 150° Fahr.; now take a will do. The solution should be sufficient small porous cell and fill it with this cyanide in quantity to gild the articles at once, so solution, and place it inside the gallon of solu- that it should not have to be done bit by bit; tion; into this cell is put a small plate of iron for when there is a part in the solution and a or copper, and attached by a wire to the zinc part out, there will generally be a line mark pole of a battery. A piece of gold is placed at the point touching the surface of the soluinto the large solution, facing the plate in the tion. The rapidity with which metals are porous cell, and attached to the silver of the acted upon at the surface line of the solution battery. The whole is allowed to remain in is remarkable. If the positive electrode is action until the gold, which is to be taken out not wholly immersed in the solution, it will, from time to time and weighed, has lost the in a short time, be cut through at the surface quantity required in solution. By this means a solution of any strength can be made, according to the time allowed. The solution in the porous cell, unless the action has continued long, will have no gold, and may be thrown away. Half an hour will suffice for a small quantity of solution-of course any quantity of solution may be made up by the of the water, as if cut by a knife. This is also the case in silver, copper, and other solutions. 3733. To Maintain the Strength of the Gold Solution. As the gold solution evaporates by being hot, distilled water must from time to time be added. The water should always be added when the operation of gilding is over, not when it is about to be commenced, or the solution will not give so satisfactory a result. When the gilding operation is continued successively for several days, the water should be added at night. To obtain a deposit of a good color, much depends upon the state of the solution and battery; it is therefore necessary that strict attention be paid to these, and the more so as the gold sothe solution just as the articles are being put in; or, what is better, add some sulphuret of carbon in the same way as for silver solutions (see No. 3710), which affects the color and appearance of the gold in the same way as it does the silver. 3735. To Improve the Color of Gilding. A defective colored gilding may be improved by the help of the following mixture:

lution is very liable to change if the size of 3 parts nitrate of potassa (saltpetre), 1½ parts 'the article receiving the deposit is not the alum, 14 parts sulphate of zinc, and 14 parts same as that of the positive electrode plate. common salt, are put into a small quantity of The result of a series of observations and ex- water, to form a sort of paste, which is put periments, continued daily throughout a upon the articles to be colored; these are period of nine months, showed that in five then placed upon an iron plate over a clear instances only the deposit was exactly equal fire, so that they will attain nearly to a black to the quantity dissolved from the positive heat, when they are suddenly plunged into plate. In many cases the difference did not cold water. This gives them a beautiful high exceed 3 per cent., though occasionally it rose color. Different hues may be had by a variato 50 per cent. The average difference, how- tion in the mixture. ever, was 25 per cent. In some cases double 3736. Το Electro-gild with Red the quantity dissolved was deposited, in Gold. Gold having the red color of 14 carat others the reverse occurred-both resulting gold may be deposited by the battery in the from alterations made in the respective pro- following manner: Prepare a solution of cesses; for in these experiments, the state of cyanide of copper by adding cyanide of potasthe solution and the relative sizes of the neg- sium to a solution tion of sulphate of copper until ative and positive electrodes were varied, as the precipitate at first thrown down is redisfar as practicable. The most simple method solved. Add to this a solution of cyanide of of keeping a constant register of the state of gold (see No. 3727) in sufficient quantity to the solution is to weigh the gold electrode give, on trial, the desired color of gold debefore putting it into the solution; and, when posit. When using this solution, the positive taking it out, to compare the loss with the electrode plate should be of gold of the same amount deposited. A little allowance, how- color as that desired to be deposited. ever, must be made for small portions of 3737. Practical Suggestions in Elecmetal dissolved in the solution, from the arti-tro-gilding. According to the amount of cles that are gilt, which, when gilding is per- gold deposited, so will be its durability. A formed daily, is considerable in a year. A few grains will serve to give a gold color to a constant control can thus be exercised over very large surface, but it will not last. This the solution, to which there will have to be proves, however, that the process may be added from time to time a little cyanide of potassium, a simple test of requirement being that the gold positive electrode should always come out clean, for if it has a film or crust it is a certain indication that the solution is deused for the most inferior quality of gilding. Gold thinly laid upon silver will be of a light color, because of the property of gold to transmit light. The solution for gilding silver should be made very hot, but for copper ficient of cyanide of potassium. Care must it should be at its minimum heat. A be taken to distinguish this crust, which is occasionally dark-green or black, from a black appearance, which the gold electrode will take when very small in comparison to the article being gilt, and which is caused by the tendency to evolve gas. In this case an addition of cyanide of potassium would increase the evil. The black appearance from the tendency to the escape of gas has a slimy appearance. This generally takes place when the solution is nearly exhausted of gold, of which fact this appearance, taken conjointly with the relative sizes of the electrodes, is a sure guide. mere blush may be sufficient for articles not subjected to wear; but on watch cases, pencil cases, chains, and the like, a good coating should be given. An ordinary sized watch case should have from 20 grains to a pennyweight; a mere coloring will be sufficient for the inside, but the outside should have as much as possible. A watch case thus gilt, for ordinary wear, will last five or six years without becoming bare. Small silver chains should have 12 grains; pencil cases of ordinary size should have from three to five grains; a thimble from 1 to 2 grains. These suggestions will serve as a guide to amateur gilders, many of whom, having imparted only a color to their pencil cases, feel disappointed upon seeing them speedily become bare; hence arises much of the obloquy thrown upon the process.

3738. To Deposit Copper, Silver, or Gold by the Battery on Paper and other

3734. To Regulate the Color of the Gilding. The gold upon the gilt article, on coming out of the solution, should be of a dark yellow color, approaching to brown; but this, when scratched (see No. 3709), will yield a beautifully rich deep gold. If the color is blackish it ought not to be finished, for it will never either brush or burnish a good color. Fibrous Material. The whole question is If the battery is too strong, and gas is given to make the paper a good conductor of elecoff from the article, the color will be black; tricity without coating it with a material if the solution is too cold, or the battery which may peel off. One of the best methods rather weak, the gold will be light-colored; is to take a solution of nitrate of silver, pour so that every variety of shade may be impart- in liquid ammonia till the precipitate at first ed. A very rich dead gold may be made by formed is entirely dissolved again, and place adding ammoniuret of gold (see No. 3725) to the paper, silk, or muslin for one or two hours in this solution. After taking it out and dry- for two hours. The metallic article, if not ing well, it is exposed to a current of hydrogen copper, is covered with a film of copper simgas, by which operation the silver is reduced ultaneously with its being immersed into the to a metallic state, and the material becomes boiling gilding liquor, by placing a piece of so good a conductor of electricity that it may sheet-copper along with it. As soon as a debe electroplated with copper, silver, or gold, in posit of copper is observed, the piece of copthe usual manner. per is taken out, and the liquor continued

3739. To Dissolve Gold from Gilt boiling until a deep yellow color is obtained. Articles. Before regilding articles which are partly covered with gold, or when the gilding is imperfect, and the articles require regilding, the gold should be removed from them by putting them into strong nitric acid; and when the articles have been placed in the acid, by adding some common salt, not in solution, but in crystals. By this method gold may be dissolved from any metal, even from iron, without injuring it in the least. After coming out of the acid, the articles must be polished. The best method, however, is to brush off the gold as described for silver (see No. 3706), which gives the polish at the same time.

3740. To Recover Gold from its Acid Solution. When the acid has become saturated by the gold that has been dissolved in it, or when it ceases to dissolve the gold rapidly, The article is then taken out, washed off with water, and rubbed with a metallic brush.

When the liquor has again become clear by settling and decanting, it is again heated to boiling, the article immersed, while the piece of copper is moved about in the fluid without touching the other. The same operation may be renewed ad libitum, until the desired thickness of gold is obtained.

3744. Plating and Gilding Without a Battery. Watts gives the following very useful solution of silver or gold for plating or gilding without the aid of a battery: Take 1 ounce nitrate of silver, dissolved in 1 quart distilled or rain water. When thoroughly dissolved, throw in a few crystals of hyposulphite of soda, which will at first form a brown precipitate, but which eventually becomes redissolved if sufficient hyposulphite it is diluted with several times its bulk of has been employed. A slight excess of this water, and then soda or potash added till the salt must, however, be added. The solution greater portion of the acid is neutralized. A thus formed may be used for coating small solution of sulphate of iron (copperas) is then articles of steel, brass, or German silver, by added, so long as a precipitate is formed; when this settles down it is carefully collected upon a paper filter, washed and dried, and then fused in a crucible with a little borax and common salt, when the gold is found as a button at the bottom of the crucible. When the gold is brushed off, the brushings are burned at a red heat, and the residue fused with carbonate of soda and a little borax; in this case, the gold will not be pure, and will have to be refined.

3741. To Separate Gold from Gilt Copper or Silver. Take a solution of borax in water, apply to the gilt surface, and sprinkle over it some finely powdered sulphur; make the article red hot, and quench it in water; then scrape off the gold, and recover it by means of lead. (See No. 3191.) simply dipping a sponge in the solution and rubbing it over the surface of the article to be coated; the silver becomes so firmly attached to the steel (when the solution has been carefully made) that it is removed with considerable difficulty. A solution of gold may be made in the same way, and applied as described.

A concentrated solution of either gold or silver, thus made, may be used for coating parts of articles which have stripped or blistered, by applying it with a camel-hair pencil to the part, and touching the spot at the same time with a thin clean strip of zinc.

3745. To Distinguish Gold from its Imitations. The ordinary method of testing gold by the touchstone is founded upon the insolubility of this metal in nitric acid. If a mark be made on the touchstone with the article under examination, the gold is not dissolved by this acid, whereas golden colored alloys of inferior value are dissolved and disappear immediately. When articles are very thinly gilded, the detection of the gold in this manner is uncertain, in which case the 3742. To Recover Gold from Gilt Articles. Gold may be stripped from articles that have been gilt by placing them in strong nitric acid, in which some salt has been previously dissolved. When a number of articles have been stripped in the solution, it begins to work slowly, and it is time then to following method may be used with advanabandon it, and use a new one. The gold may tage. (See No. 3190.) then be recovered from the old solution, by 3746. Test Fluid for Gilded Artievaporating it to dryness, and fusing the resi- cles. A little carbonate of copper is put into duum with a small piece of soda or potash, the gold being fused into a button. The addition of a little saltpetre will tend to make the refining process more complete. As there is some trouble connected with this process, it is scarcely worth adopting where very small per is diluted for use with from 10 to 11 a test-tube, and to this is added, drop by drop, pure hydrochloric acid, till the blue powder has dissolved to a clear green fluid, occasionally warming it over a spirit lamp.

This concentrated solution of chloride of copquantities of gold are concerned. In such a times its volume of distilled water. case it is a better plan to suspend the article, 3747. Το Test Gilded Articles. Befrom which the gold is to be removed, in the gilding bath, in the place of the anode, when gilding another article. fore testing, the metallic surface must be well cleaned. This can be done effectually ly brushing it for a minute or two with a little 3743. Electro-Gilding Without a spirits cf wine, or, better, with absolute al- Battery. Dissolve 9 parts terchloride of cohol. The surface having dried, a little of gold in 1000 to 2000 parts pure water; then the testing fluid (see last receipt) is dropped add 360 parts bicarbonate of potassa, and boil on and allowed to remain in contact for about a minute. The fluid is then removed by shoots out from the negative electrode like means of a small pipette, and the surface of feelers, towards the positive, which it reaches the metal completely dried with bibulous in a few seconds. The space between the paper; if no dark spot be then visible, the ar- poles seems like a mass of crystallized threads, ticle is coated with pure gold. If the metallic and the electric current passes through them surface is but lightly gilded, a very slight without affecting further decomposition. So blackening is sometimes remarked, which tender are these metallic threads that when may throw a doubt upon the result. In such lifted out of the solution they fall upon the a case, to make quite certain, a little of the plate like cobweb. Seen through a glass they surface may be scraped off, and then the test- exhibit a beautiful crystalline structure. Tin ing fluid again applied. If a dark spot is then may also be deposited from its solution in perceived, the article may be considered as caustic potash or soda. very thinly gilded.