58 PYROMETALLURGY. ^ [ill. 



more silver when the former proportion is used, even with the 

 use of strong acid and after continued hoiling. He found 

 further that only If silver to 1 gold was really necessary to 

 obtain a correct separation. We employ 2 to 1 in the United 

 States Mint. 



Pettenkofer further observes that all commercial silver, not 

 subjected to chemical separation, contains platinum. To 

 prove the presence of platinum in parted gold, it is alloyed 

 with 2-2J pts. silver, parted in the usual way by nitric acid, 

 precipitated by dilute muriatic acid, filtered, the solution 

 evaporated to dryness (at a gentle heat), the residue treated 

 with alcohol, and the platinum precipitated from the solution by 

 salammoniac. To determine it quantitatively, D'Arcet alloys 

 two equal portions of the gold with silver, extracts one with 

 nitric and the other with sulphuric acid ; the excess of weight 

 in the latter over the former is platinum. 



Pettenkofer's discovery of platinum in the gold and silver 

 is of some importance, for it serves to explain in part the 

 refining effects of nitre on gold. By this fusion an appreciable 

 quantity of gold is taken up by the nitre at the same time, 

 although gold alone is slightly affected by it. After treating 

 with water the slags resulting from toughening gold by nitre, 

 the fine gray sediment contains alumina, silicic acid, potassa, 

 oxides of iron, copper, lead, platinum, gold, and metallic gold. 



Cleansing Silver. — It is said that silver or brass vessels may 

 be cleansed by boiling them in water with calcined hartshorn in 

 powder (30 grms. to 1 quart water), then drying them by the 

 fire, and rubbing them w^hen dry with woollen rags saturated 

 with the above liquid and subsequently dried. The polish is 

 heightened by further friction with a chamois-skin. 



Gold. — For a full description of the Orange Grove or 

 Vaucluse gold mine, in Virginia, see Amer. Journ. 2d ser. vii. 

 295, with analyses of the ore by J. C. B. 



California G-old. — Of the following analyses, 1 is by Os- 

 wald ; 2 by T. H. Henry, of the small flattened grains, spec, 

 gray. 15.63 ; 3 by the same, of a larger piece with irregular 

 surface and siliceous gangue, spec. grav. 15.96. 



