3214. To Purify and Reduce Silver

3214.    To Purify and Reduce Silver. Silver, as used in 'the arts and coinage, is alloyed with a portion of copper. To purify it, dissolve the metal in nitric acid slightly diluted, and add common salt, which throws down the whole of the silver in the form of chloride. To reduce it into a metallic- state several methods are used. The chloride must be repeatedly washed with distilled water, and placed in a zinc cup ; a little diluted sulphuric acid being added, the chloride is soon reduced. The silver, when thoroughly washed, is quite pure. In the absence of a zinc cup, a porcelain cup containing a zinc plate may be used. The process is expedited by warming the cup. (See No. 3536 (To Obtain Pure Silver in Powder).)

3215. To Purify and Reduce Silver

3215.    To Purify and Reduce Silver. Proceed as above, and digest the washed chloride with pure copper and ammonia. The quantity of ammonia need not be sufficient to dissolve the chloride. Leave the mixture for a day, then wash the silver thoroughly. Or: Boil the washed and moist chloride in solution of pure potash, adding a little sugar; when washed it is quite pure.

3216. Peale's Method of Obtaining Pure Silver from its Solutions

3216.    Peale's Method of Obtaining Pure Silver from its Solutions. By adding in excess, a saturated solution of common salt to the solution of nitrate of silver, the metal is thrown down, as an insoluble salt, the chloride of silver. The precipitate must then be carefully washed until it is entirely freed from the presence of nitric acid. Granulated zinc must then be added to the chloride, and stirred through the mass. The finer the zinc has been granulated, the more rapid wiill be the reduction. Dilute sulphuric acid must also be added, and the whole stirred until the reduction is complete, which will bo known by the entire disappearance of the white chloride, and its conversion into a grey powder. A new set of affinities takes place with great rapidity in this combination, and the chlorine is liberated from the silver, which takes its metallic form, as above stated, in the appearance of a grey powder. The zinc, having been added in excess, must now be removed by the addition of dilute sulphuric acid ; after all action has ceased, the solution of zinc must be decanted, or drawn off with a syphon, and the silver washed until free from acidulous matter, after which it may be dried by pressure, or the simple application of heat in a pan over the fire, when it will be ready for melting, with the usual fluxes, or re-solution with nitric acid. This process is rapid and easy; is not subject to loss; it will yield, in the terms of trade, pure silver, of a quality from 994 to 998 thousandths fine, and is therefore well adapted to the preparation of pure nitrate of silver for the use of photographers and all others who need a reliable article.

3217. Silver Dust

3217.     Silver Dust. Take silver, dissolve it in slightly diluted nitric acid, and precipitate it with slips of bright copper; wash the powder in spirits, and dry it. Or : An exceedingly fine silver dust may be obtained by boiling recently precipitated chloride of silver with water acidulated with sulphuric acid, and zinc.