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To Clean Gold Ornaments

Gold ornaments may also be thoroughly cleaned by immersion for a few seconds in a weak solution of ammonia. Then wash with soap and water. 3204. Polishing Powder for Gold Articles. Dr. W. Hofman has analyzed a polishing powder sold by gold workers in Germany, which always commands a very high price, and hence, it may be inferred, is well adapted for the purpose. He found it to be a very simple composition, being a mixture of about 70 per cent. sesquioxide of iron 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 procipitate, and the assay cannot then be depended on. Instead of weighing the quantity of test liquor used, a tube graduated into To prepare it, protochloride of iron, obtained used instead, every division of which required by dissolving iron in hydrochloric acid, is to throw down the silver, will represent the treated with liquid ammonia until a precipi- roth of a grain. The tube being filled to the tate is no longer formed. The precipitate is 0, is ready for use, and from being graduated collected on a filter, and, without washing, is downward the quantity poured out may at dried at such a temperature that the adhering sal-ammoniac shall not be volatilized. The protoxide of iron precipitate at first becomes charged with sesquioxide. (iron rust) and 30 per cent. sal-ammoniac. 100 parts, and holding 1000 grains, may bo ery white S ilver. This metal has a very white color, a high degree of lustre, is exceedingty 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. $3203. 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.) 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 be 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, once be 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. 3208. Test Solution for Assaying Silver. Dissolve 541 grains pure sea-salt (sce No. 3200) in 22 ounces 3204 grains (avoirdupois) distilled water. Filter and keep in a stoppered bottle for use.