The old process for separating silver from waste was as follows: The refuse was mixed with an equal quantity of charcoal, placed in a crucible, and subjected to a bright-red heat, and in a short time a silver button formed at the bottom. Carbonate of soda is another good flux.
Silvering Glass Globes.
Silvering Powder For Metals.
Silver Testing.
A testing solution of potassium bichromate, 1 ounce, pure nitric acid, 6 ounces, and water, 2 ounces, gives the following results on surfaces of the metals named:
| Metal. | Color in one minute. | Color of mark left. |
|---|---|---|
| Pure silver | Bright blood-red | Grayish white |
| .925 silver | Dark red | Dark brown |
| .800 silver | Chocolate | Dark brown |
| .500 silver | Green | Dark brown |
| German silver | Dark blue | Light gray |
| Nickel | Turquoise blue | Scarcely any |
| Copper | Very dark blue | Cleaned copper |
| Brass | Dark brown | Light brown |
| Lead | Nut brown | Leaden |
| Tin | Reddish brown | Dark |
| Zinc | Light chocolate | Steel gray |
| Aluminum | Yellow | No stain |
| Platinum | Vandyke brown | No stain |
| Iron | Various | Black |
| 9-carat gold | Unchanged | No stain |
The second column in the table shows such change of color as the liquid—not the metal—undergoes during its action for the period of 1 minute. The test liquid being then washed off with cold water, the third column shows the nature of the stain that is left.
In the case of faintly silvered goods, such as buttons, this test fails, since the slight quantity of resulting silver chromate does not become visible or dissolves in the nitric acid present. But even such a thin coat of silver can be recognized with the above test liquor, if the bichromate solution is used, diluted with the equal volume of water, or if a small drop of water is first put on the article and afterwards a little drop of the undiluted solution is applied by means of a capillary tube. In this manner a distinct red spot was obtained in the case of very slight silvering.
A simpler method is as follows: Rub the piece to be tested on the touchstone and moisten the mark with nitric acid, whereupon it disappears. Add a little hydrochloric acid with a glass rod. If a white turbidness (silver chloride) appears which does not vanish upon addition of water, or, in case of faint silvering or an alloy poor in silver, a weak opalescence, the presence of silver is certain. Even alloys containing very little silver give this reaction quite distinctly.