d. (R. Siemens.) As a reducing agent, acetic aldehyde is used in the form of aldehyde ammonia, prepared by passing dry ammoniacal gas into aldehyde. Four grams of silver nitrate and 21⁄2 grams of aldehyde ammonia are separately dissolved in a litre of distilled water, and the solutions mixed and filtered. The article to be silvered, after washing out with potassium carbonate, and then with spirits of wine and distilled water, to remove every trace of grease, is filled with this solution (as far as it is desired to silver), and then hung up in the water bath.
It is now gradually heated, and as soon as the temperature reaches 50° C. the separation of the silver mirror begins, and soon spreads over the whole inner glass surface. Its formation is soon finished, usually between 55° or 60°. When the beauty of the silver surface reaches a maximum it is time to withdraw the article from the water bath, and pour off the contents, or the brilliancy of the mirror will be impaired. The article is finally rinsed in distilled water.
e. (Martin.) M. Martin makes use of four liquids, viz., first, a 10 per cent. solution of nitrate of silver; second, liquor ammoniæ, sp. gr. ·970; third, a 4 per cent. solution of caustic soda; and fourth, a 121⁄2 per cent, solution of white sugar, to which he adds 21⁄2 per cent. of nitric acid, and after twenty minutes’ boiling he adds to it 25 parts of alcohol and water, to make up the bulk to 250. The silvering solution is made by mixing together 12 parts of solution No. 1, 8 parts of No. 2, 20 parts of No. 3, and 60 parts of distilled water, and finally, in twenty-four hours, 10 parts of No. 4. The object to be silvered is then immersed, when it will be covered with a film of reduced silver, which in ten minutes’ time will be sufficiently thick for use. After having been washed with distilled water and dried the surface may be polished with chamois leather and rouge.
Silvering of Metals. 1. (Leaf silvering.) This is performed with leaf silvering in the way described under Gilding for the gilding of polished metals.
3. (Cold silvering.) Mix chloride of silver, 1 part, with pearlash, 3 parts, common salt, 11⁄2 part, and whiting, 1 part; and well rub the mixture on the surface of the brass or copper (previously well cleaned), by means of a piece of soft leather, or a cork moistened with water and dipped into the powder. When properly silvered the metal should be
well washed in hot water slightly alkalised, and then wiped dry.
3. (Electeo-silvering.) This is described under Electrotype.
Silver, A New Imitation of. A patent for an alloy has been taken out by M. Lemarquand, which is said to bear a close resemblance to silver in appearance, and to be unaffected by atmospheric influences. It has the following composition:—
| Pure copper | 750 | parts. |
| Nickel | 140 | ” |
| Black oxide of cobalt | 20 | ” |
| Tin, in sticks | 18 | ” |
| Zinc | 72 | ” |
SIMAROU′BA. Syn. Simaruba (Ph. E. & D.), L. The root-bark of Simaruba amara or officinalis, the mountain damson. Tonic, bitter, and astringent.—Dose, 20 to 30 gr.; in intermittents, obstinate diarrhœa, dysentery, and dyspepsia.