212 ON OSMIUM AND IRIDIUM, FROM N.S.W. GOLD, 



hot, into a strong solution of Sal ammoniac, when the greatest 

 part of the Iridium falls down as a blackish crystalline powder, 

 having a dark red streak, and which is a double salt of Chloride 

 of Ammonium with Chloride of Iridium or Irid-Salmiak. 



The liquid, which is filtered off from the Irid-Salmiak, is 

 evaporated with soda to dryness, gently heated in an earthen 

 crucible, and then boiled out with water, which leaves Oxide of 

 Iridium behind as a blackish powder, which is dried and reduced 

 to Iridium by Hydrogen gas. 



The purest Iridium is obtained by heating the Irid-Salmiak, 

 just mentioned, to a strong red heat, when pure Iridium is left 

 behind if the Irid-Salmiak employed has been once or twice 

 recrystallized. In this way I obtained the Iridium here produced. 

 It is a black powder. Subjected to strong pressure whilst some- 

 what moist in a suitable apparatus, and then to a strong white heat, 

 the Iridium is obtained in a compact, though very brittle mass, 

 which allows of polish. I endeavoured to obtain a little in this 

 way ; its colour is that of polished steel. (Specimen shown.) 



This Iridium, which obtained its name from the Greek word 

 Ipt?, because it forms different salts, the solutions of which possess 

 almost all colours of the rainbow, is extremely difficult of fusion. 

 At a heat by which platinum is fused, it merely contracts a little 

 and gets silver white. Of late Messrs. Deville and Debray, in 

 Paris, who have occupied themselves very largely with the ex- 

 traction of platinum and platinum metals have been especially 

 successful in the construction of furnaces for obtaining the 

 highest degrees of heat. These furnaces are constructed of lime, 

 and heated with a mixture of either coal gas and oxygen, or 

 oxygen and hydrogen, in the proportion of 1 oxygen to 2 hydro- 

 gen. In this furnace they have been able to melt about 400 

 grains of pure Iridium in one operation, whilst the same furnaces 

 fused about 25 Ibs. of platinum in one operation. The Iridium 

 thus fused -is pure white and similar to polished steel, but brittle 

 from its crystalline structure within. Its specific gravity is the 

 same as Platinum, namely, 21*15 ; it alloys with Zinc and Tin. 

 The Iridium as obtained as black powder, is used as the best 

 black colour for porcelain painting. But its most important 

 application appears to have been discovered but quite lately, 



