56 PYROMETALLURGY. [ill. 



for every 2 pts. of chloride. By heating the crucible more 

 intensely, the silver will run together, and may be separated 

 by mechanical means. The reducing power of the charcoal 

 is owing to its content of hydrogen. 



Levol dissolves sugar in potassa Ije, and boils chloride of 

 silver in it. The chloride is reduced to a gray metallic pow- 

 der, while carbonic acid is evolved (Journ. de Chim. Med.) 



C. Zimmermann employs the following method for large quan- 

 tities (Gewerbvereinsbl. der Prov. Preussen, 2 Jahrg. 1847). 

 The washed chloride is mixed with water, pieces of bar-iron 

 of the size of a finger thrown in, and the whole stirred with 

 wood in a stoneware or porcelain vessel. 2ft) of iron are re- 

 quired for so much chloride as contains 8 marks of fine silver, 

 and the reduction is completed in 2 hours. The washed and 

 dried silver powder is fused in a clay crucible, Avith a mixture 

 of equal parts of potash and dry salt. 



This reduction is performed at the United States Mint, by 

 granulated zinc and sulphuric acid, on about lOOOft) of silver 

 per day, and presents advantages which the use of iron does 

 not. There is not a great difference in the cost between clean 

 bar-iron prepared as above, and granulated zinc, and, of the 

 two, the latter is freer from injurious ingredients. As in 

 the precipitation of silver from large parting (quartation) 

 operations, the exact quantities of silver cannot readily be 

 known ; and as an excess of metal will be required to insure 

 total and rapid reduction, this excess must be removed either 

 by sulphuric acid or by sifting. The latter would be incon- 

 venient, and the zinc is dissolved more rapidly than iron would 

 be. Moreover, the reduction proceeds more rapidly with zinc, 

 since it can be readily procured in a state of fine division by 

 granulating. In melting the fine silver into toughened bars, 

 we use saltpeter and borax. The silver thus obtained, with- 

 out attempting to procure it very pure, shows a fineness of 

 995-997|, and may be easily refined in the pot to 998 and 

 999 thousandths.— J". 0. B. 



Parting hj Sulphuric Acid. — Pettenkofer's experiments on 

 parting gold by oil of vitriol are of some value. In this 



