114 PLATINUM METALS AND ORE. 



acid. It is very volatile, condenses in colorless crys- 

 tals, soluble in water, with a very pungent odor ex- 

 tremely irritating and deleterious to the eyes and 

 organs of respiration. If passed in the vapor form 

 with hydrogen through a glass tube heated to redness, 

 it is reduced to a mirror of metallic osmium. The 

 solution heated with sulphurous acid becomes violet. 

 Potassa precipitates a black oxide containing potassa, 

 and easily reduced by hydrogen. The solution be- 

 comes yellow with potassa and ammonia. The osmiate 

 of potassa is deep yellow crystalline. Its solution 

 mixed with alcohol precipitates dark red crystalline 

 osmite of potassa KO, Os O,. If chloride of ammo- 

 nium is added to this last solution, a pale yellow crys- 

 talline salt of ammonium and osmium is precipitated, 

 which, after it is ignited in a current of hydrogen, 

 leaves metallic osmium. 



Both the chlorides of osmium are volatile. The 

 protochloride, Os Cl, is green, the bichloride, Os C1 2 , is 

 dark red. The double chloride, KCl-fOsCl 2 , forms 

 dark-brown octahedrons, giving a yellow solution in 

 water. 



PLATINUM ORE. 



(Platinum with small quantities of Iridium, Palla- 

 dium, Rhodiurn ; Osmium, Ruthenium, Iron and Copper.) 



The commercial platinum ore usually contains grains 

 of sand, of osmium, iridium, and often of gold. In 

 order to find the latter the mass is digested in rather 

 dilute aqua-regia, until scales of gold are no longer 

 visible. The solution is then poured off from the 

 undissolved platinum, freed from nitric acid by eva- 

 poration, diluted, oxalic acid added, and the gold pre- 

 cipitated by means of heat. It is washed, ignited, and 

 weighed. 



The sand is determined in the following manner: 

 A small quantity of borax is fused in a clay crucible, 



