ANALYSIS OF ORES OF SILVER.

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plate, is then rolled under steel rollers, moved by machinery,till it is of a certain thickness; it is afterwards cut to a greateror less extremity according to the use for which it is intended.

An ounce of silver is often rolled out into a surface of aboutthree square feet, and its thickness is about the three thousandthpart of an inch ; and hence we need not wonder at the silverbeing soon worn off from the sharp edges of plated copper, whenit is rolled to so great an extent.

Remark. ..What is commonly called French plate, is not tobe confounded with plated copper. French plate is made byheating copper, or more commonly brass, to a certain degree;silver leaf is then applied upon the heated metal, to which it ad-heres by being rubbed w r ith a proper burnisher.

ANALYSIS OF ORES OF SILVER.

The analysis of the ores of silver has been always consideredas very important, on account of the great value of the metalwhich they contain in abundance.

The ore, called native silver, is to be dissolved in nitric acid.The gold, if the ore contains any, remains in the state of a blackpowder, and may be dried and weighed. The silver may thenbe precipitated, by adding to the solution common salt. Everyhundred parts of the dried precipitate, denote about /5 parts ofsilver. But, as lead may be present in the solution, and thismetal is also precipitated by the muriatic acid of the commonsalt, it may be proper to immerse in the solution which shouldnot have an excess of acid a polished plate of copper. Thiswill precipitate the silver in a metallic form. The muriate ofsilver is soluble in liquid ammonia, but that of lead is not.The presence of copper may be ascertained by the green colourof the solution, and by the blue colour which it assumes on add-ing to it ammonia. The copper may be precipitated by immers-