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Silver

pure, acid and nitric

SILVER (Symbol, Ag ; atomic weight, 108).A white metal which when quite pure is rather softer than gold, and not quite so soft as lead. It is the best known conductor of both heat and electricity. Its great use in photography is due to the fact that it forms compounds exceedingly sensitive to light.

In consequence of its softness all silver for the manufacture of coins and articles is mixed with copper ; American coinage contains 10.13i parts of pure silver in tz parts. The following method of obtaining pure silver from coins is given by Wall : Place the coin, either entire or, preferably, cut up small, in a test tube, with one part of pure nitric acid and two parts of water ; apply a gentle heat, and an action commences at once, orange-red fumes of nitric oxide being evolved. If after the lapse of some time the whole of the coin is not dissolved, add more nitric acid, and again apply heat. When the coin is dissolved, the solution will be seen to be of a bright blue color, due to the copper ; pure silver can be obtained from this solution by evaporating to dryness and fusing strongly the resulting mass. A little taken out and dissolved in water should

give no blue coloration with solution of ammonia ; or sheet copper may be placed in the acid solution, when a precipitate of pure silver will take place, which may be collected and again dis solved in nitric acid to form solution of nitrate of silver ; or the precipitate may be collected and fused as above to obtain a button of silver. An United States dollar contains 370 grains of pure silver and 3o parts of alloy.

Silver is soluble in nitric acid and boiling sulphuric acid, and partially in hydrochloric acid, and combines directly with chlorine, bromine, and iodine.

Water at ordinary temperature, and air free from sulphuretted hydrogen, have no effect upon it, tarnishing being due to the sulphuretted hydrogen contained in the air.

Silver is principally employed in photography in the manufacture of silver nitrate (q .) .