PARTING BY NITRIC ACID. 57 







process, gold may be extracted from silver, even when it forms 

 an exceedingly minute proportion in the latter, by boiling it 

 with oil of vitriol in iron or platinum vessels, and a large 

 amount of gold has been thus recovered from old silver, since 

 the process was first made known. To effect the parting most 

 completely, there should be in 16 pts. alloy 3 to 4 pts. gold, 

 and at least 10 of silver. Pettenlcofer's experiments were made 

 in the refinery at Munich, with Kronenthaler (crown-dollars), 

 which contain yuoauu of gold. The parting is at first rapid 

 until the fineness reaches 958 to 960 thousandths, when long- 

 continued boiling (14 times) with great excess of acid raises 

 it only to 970-972 thousandths, when it consists of 970 gold, 

 28 silver, and 2 platinum. No excess of acid nor repeated 

 boiling will raise this spongy gold more than \ thousandth 

 beyond this. It may, however, be refused with nitre, alloyed 

 with silver, and again parted by oil of vitriol. It would ap- 

 pear, from his experiments, that the silver is alloyed in the 

 metallic state with the spongy gold, and not combined with 

 chlorine, phosphorus, nor arsenic ; but it powerfully resists 

 all attempts to extract it, whether by sulphuric or nitric acid. 

 Sulphur may be distilled over it without its forming sul- 

 phuret of silver. Treated with boiling sulphuric acid to which 

 bichromate of potassa has been added, a considerable amount 

 of gold is dissolved, while sesquioxide of chrome is formed ; 

 but neither silver nor platinum, which is also present, is at- 

 tacked. Pettenkofer thinks that the silver is in a different 

 state from its normal condition. The silver may be extracted 

 by fusion with bisulphate of potassa or soda. It is probable 

 that the great preponderance of gold assimilates the alloyed 

 silver to itself, just as silver alloyed with platinum renders 

 the latter soluble in nitric acid, and as platinum in gold sub- 

 jects the latter to more powerful corrosion by fusion with 

 nitre. 



Parting hy Nitric Acid, or Quartation. — Pettenkofer con- 

 firms the results of Kandelhardt and Chaudet, that the ancient 

 proportion of 3 silver to 1 gold is unnecessary, but that 2| 

 silver to 1 gold is a far better proportion ; for the gold retains 



