Silver. This metal has a very white color, a high degree of lustre, is exceedingly malleable and ductile, and the best conductor of heat and electricity known. It is procured from its ores chiefly by amalgamation and cupellation. Its specific gravity is 10.474, and melting-point 1873° Fahr., or bright redness. It is soluble in nitric acid, and in sulphuric acid by the aid of heat. Its surface is rapidly tarnished by sulphuretted hydrogen, and by the fumes of sulphur.

3206. Assay of Silver by Cupellation

3206. Assay of Silver by Cupellation. The assay pound (usually 12 or 20 grains for silver) of the alloy for examination is accurately weighed, and then wrapped in a small piece of paper ready to undergo the process of cupellation. (See No. 3191 (Assay of Gold by Cupellation).) The quantity of lead used is not uniform, but depends on the nature of the alloy. It should be 16 times the weight of the copper presumed to be present in the sample. This, however, cannot bo accurately ascertained, though an experienced assayer is generally able to guess very nearly the amount. If too much lead be used, the button obtained by cupellation will be too small, owing to some of the silver being absorbed by the cupel; and if too little be used, the button will come out too large, from still containing some copper. The importance of justly proportioning the lead to the quantity of copper present in the alloy, cannot bo too much insisted on. (Cooley).

3207. Assay of Silver by Chemical Analysis

3207. Assay of Silver by Chemical Analysis. Dissolve 10 grains of the alloy in 100 grains of nitric acid, specific gravity 1.23, by the aid of heat; the solution being made in a tall stoppered glass tube, furnished with a foot; then place it in a very delicate balance, which must be brought into an exact state of equilibrium, and add the test solution (see No. 3208 (Test Solution for Assaying Silver)) gradually and cautiously, until the whole of the silver be thrown down; but the utmost care must be taken not to exceed this point. The number of grains now required to restore the equilibrium of the scales gives the exact quantity of pure silver present in 1000 parts of the sample. The addition of th3 test liquor to the solution requires the utmost exactness. After each addition the stopper should be placed in the tube, and the latter violently agitated for a short time, when the liquor will rapidly clear and enable it to be seen when the operation is concluded. We must then, as a check, add a small quantity of a solution of nitrate of silver to the liquor in the tube, after having first carefully taken the weight. If too much of the test liquor has been added, this will produce a fresh precipitate, and the assay cannot then be depended on. Instead of weighing the quantity of test liquor used, a tube graduated into 100 parts, and holding 1000 grains, may bo used instead, every division of which required to throw down the silver, will represent the 1/10 th of a grain. The tube being filled to the 0, is ready for use, and from being graduated downward the quantity poured out may at once bo read off. Generally speaking, however, measuring does not admit of the same accuracy as weighing. The termination of the operation is clearly marked, when, on adding a minute quantity of the test liquor to the silver solution, no cloudiness occurs.