118 IRIDOSMINE AND PLATINUM RESIDUES. 



71. IRIDOSMINE AND PLATINUM RESIDUES. 



I. Iridosmine occurs in small scales and mostly steel 

 colored, extremely hard, and of sp. gr. 18 to 20. It is 

 contained entirely in the residue in the solution of 

 platinum, mostly in the form of very fine plates. Its 

 composition is variable. Besides the two principal 

 metals, it contains more or less rhodium and ruthenium, 

 with small quantities of platinum, copper, and iron. 

 It is insoluble in aqua regia. 



The osmium may be extracted for the most part 

 from the variety made up of very fine grains* or pow- 

 der by roasting. The ore is placed in a porcelain tube 

 heated to redness, and a slow stream of air or oxygen 

 gas passed over it. The end of the porcelain tube 

 passes into a well-cooled receiver, from which the 

 osmic acid is conducted into a solution of caustic 

 potassa. 



The fine pulverulent variety is mixed with an equal 

 weight of common salt, and a stream of moist chlorine 

 passed over it, in a porcelain tube heated to redness, 

 and then treated as in No. 71, II. 



In order to pulverize the coarse grained kind, it is 

 fused with six times its weight of pure zinc, in a cru- 

 cible placed in a second crucible and surrounded by 

 charcoal powder, well covered and heated to redness 

 for half an hour and to a white heat for two hours 

 until all the zinc is volatilized. The iridosmine is left 

 in the form of a glistening friable sponge. 



From this sponge the osmium may be volatilized by 



* A species in form of a very heavy gray salt, and probably ob- 

 tained from the dressing of the gold sands of California, contains 

 gtill more gold and much chloride of silver, which must be ex- 

 tracted by concentrated ammonia before it is made use of. 



Species containing sand must be purified by fusing with carbo- 

 nate of soda and treating the mass with water. 



