Electroplating. The foregoing matter refers to electrotyping, that is, copper-coating, by galvanism. Electroplating, or coating with silver, is conducted in a similar manner to electrotyping as far as general principles and manipulation are concerned, but differs in the solutions used, as well as in the preparation of the objects to be electroplated.

3697. To Prepare Cyanide of Silver

3697. To Prepare Cyanide of Silver. First dissolve 1 ounce pure silver in 2 ounces nitric acid and 2 ounces hot water, after which further dilute with 1 quart hot water. The propriety of diluting the nitrate of silver before precipitating by the cyanide of potassium arises from the fact that the salts of potash and soda (such as the nitrates, chlorides, and sulphates), when in strong solution, dissolve small quantities of the silver salt, and thus cause a loss, which is prevented by previous dilution with water. The nitric acid used must be free from hydrochloric (muriatic) acid; to a small quantity of the acid add a few drops of solution of nitrate of silver; if it gives a milky white precipitate, it contains muriatic acid, and should be rejected. Then dissolve 5 ounces cyanide of potassium in 1 quart water. Add this by degrees to the silver solution until the whole of the silver is precipitated, which may be tested thus : Stir the mixture and allow it to settle; then drop into the clear liquid a very small quantity of the second preparation, from the end of a glass rod; if the clear liquid is rendered turbid, it is a proof that the whole of the silver is not separated; but if the liquid remains unchanged, it shows that the silver is entirely separated. The clear liquid is then to be poured off, and the precipitate, which is cyanide of silver, washed at least 4 times in hot water, dried and bottled for use. The use and handling of cyanide of potassium requires great caution, as 11 grains of it are sufficient to kill a grown person. The fumes thrown off while dissolving the silver in nitric acid are also highly deleterious, and must not be inhaled; it is better, therefore, not to dissolve silver in a close room.

3698. To Make Silver Solution

3698.    To Make Silver Solution. The solution of silver used for plating consists of cyanide of silver dissolved in potassium, adding a solution of cyanide of potassium to the cyanide of silver until it is all dissolved. The resulting solution constitutes the cyanide of potassium and silver, and forms the plating solution. It ought to be filtered previous to using, as there is always formed a black sediment, composed of iron, silver, and cyanogen, which, if left in the solution, would fall upon the surface of the article receiving the deposit, and make it rough. The sediment, however, must not be thrown away, as it contains silver. The cyanide of potassium, used to dissolve the cyanide of silver, may be so diluted that the plating solution, when formed, shall contain 1 ounce of silver in the gallon; of course the proportion of silver may be larger or smaller, but that given is best for plating. In dissolving 100 ounces of silver, the following proportions of each ingredient are those which have been found in practice to be the best. Take 7 pounds of the best nitric acid, and 61 ounces of cyanide of potassinm, of the average quality; this quantity will precipitate the 100 ounces of silver dissolved in the acid solution. After this is washed, take 62 ounces more of cyanide of potassium, the solution of which will dissolve the precipitate; this being done, the plating solution is then formed. Of course these proportions will vary according to the difference in the quality of the materials; but they will servo to give an idea of the cost of the silver solution prepared in this manner.