158

METHODS OF SEPARATING SILVER FROM COPPER.

residuum, amounting to 58.75 parts, was dissolved in water;and being treated with muriate of barytes, 15 parts of sulphate ofbarytes precipitated, indicating the presence of about *5 of sul-phuric acid, or 0.75 sulphate of potash. The remaining 58 partswere muriate of potash, indicating about 21 parts of muriaticacid.*

METHOD OF SEPARATING SILVER FROM COPPER.

It is a valuable discovery of Mr. Keir, that a mixture of strongsulphuric acid with the nitrous acid, or nitrate of potash, is a pow-erful solvent of silver, though it scarcely acts upon the other me-tals. This is of considerable importance in the Birmingham ma-nufactures, where the silver in the cuttings of plated copper isrequired to be separated from this last metal. For this purposethe pieces of metal are put into a glazed earthen pan, and a com-position of eight or ten pounds of sulphuric acid, with one poundof nitrate of potash, is poured upon them, stirred, and the actionof the fluid assisted by a heat between 100° and 200° Fahr. Whenthe liquor is nearly saturated, the silver is to be precipitated by ■common salt, which may be easily afterwards reduced ; or, other-wise, the silver maybe precipitated in its metallic state by addingto the solution a few of the pieces of copper, and a sufficientquantity of water, which enables the liquor to act on the copper.The theory of this effect still remains to be investigated. :

i

The method of obtaining pure silver has been noticed already,

p. 149.

The standard silver of Great Britain contains 15 parts of silverand one of copper.

In the solder used to join different parts of silver utensils, thisproportion of copper is considerably greater, hence it is thatsuch vessels are apt to oxidate, or become covered with a greenoxid at the places where they are soldered.

Klaproth’s Beitrage, i. 132.