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

3738.    To Deposit Copper, Silver, or Gold by the Battery on Paper and other Fibrous Material. The whole question is to make the paper a good conductor of electricity without coating it with a material which may peel off. One of the best methods is to take a solution of nitrate of silver, pour in liquid ammonia till the precipitate at first formed is entirely dissolved again, and place the paper, silk, or muslin for one or two hours in this solution. After taking it out and drying well, it is exposed to a current of hydrogen gas, by which operation the silver is reduced to a metallic state, and the material becomes so good a conductor of electricity that it may be electroplated with copper, silver, or gold, in the usual manner.

3739. To Dissolve Gold from Gilt Articles

3739.    To Dissolve Gold from Gilt 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 brash off the gold as described for silver (see No. 3706 (To Prepare Articles for the Decomposing Cell)), which gives the polish at the same time.

3740. To Recover Gold from its Acid Solution

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, it is diluted with several times its bulk of water, and then soda or potash added till the greater portion of the acid is neutralized. A solution of sulphate of iron (copperas) is then 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

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 (Assay of Gold by Cupellation).)

3742. To Recover Gold from Gilt Articles

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 abandon it, and use a new one. The gold may then be recovered from the old solution, by evaporating it to dryness, and fusing the residuum 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 quantities of gold are concerned. In such a case it is a better plan to suspend the article, from which the gold is to be removed, in the gilding bath, in the place of the anode, when gilding another article.