692 OSMIUM. 



osmium combines with alkaline chlorides, and acquires greater 

 stability. The protoxide is obtained by adding potash to a so- 

 lution of this double salt ; after some hours, a deep green, almost 

 black, powder is precipitated, which is the hydrated oxide. 

 This hydrate contains alkali. It dissolves slowly but com- 

 pletely in acids, and gives solutions of a deep green colour. 



Deutoxide of osmium, Os 2 O 3 , is obtained by heating a solu- 

 tion of the osmiate of ammonia to 100 or 140, when nitrogen 

 gas is disengaged and deutoxide deposited. The oxide contains 

 ammonia. It dissolves slowly in acids, and forms yellowish 

 brown solutions, which become of a brown black when they 

 contain much oxide. The metal is not precipitated from these 

 solutions by zinc or iron. The corresponding sesquichloride of 

 osmium is obtained in combination with chloride of potassium, 

 as a double salt, when the preceding oxide containing ammonia 

 is dissolved in hydrochloric acid, and evaporated to dryness; 

 the compound is not crystalline. 



Bichloride of osmium, Os C1 2 , is the more volatile chloride 

 produced when osmium is heated in chlorine. It condenses as 

 a dark red floury powder. Exposed to air, it attracts a little 

 moisture, and forms dendritic crystals. This salt is soluble in 

 little water, giving a yellow solution, but is decomposed by a 

 large quantity, like the protochloride. The bichloride of os- 

 mium and potassium is prepared in the same manner as the 

 corresponding salt of iridium. In powder, it is of a red co- 

 lour like minium, but forms also the usual octohedral crystals, 

 KCl + OsCl 2 , which are brown. A solution of this double salt, 

 mixed with carbonate of potash or soda, affords after a time, or 

 immediately, if heated, the corresponding peroxide of osmium, 

 Os O 2 , as a brown powder, which appears black when collected. 

 It is a base capable of uniting with acids at the moment of its 

 formation. This oxide like the peroxide of iridium is reduced 

 by hydrogen at the usual temperature. 



Osmic acid, Os O 4 , or the volatile oxide of osmium is best 

 obtained by the combustion of osmium in a glass tube through 

 which a stream of oxygen gas is passed. It condenses in 

 long colourless, regular prismatic needles. The odour of this 

 compound is extremely acid and penetrating, resembling that 

 of the chloride of sulphur. It was from this property of 

 its acid, which is so constantly observed when the oxidable 

 compounds of osmium are heated in air, that osmium obtained 



