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



Ammonia, and the yellow solution which soon gets brown from 

 further decomposition, is evaporated until all Ammonia is driven 

 off, when a compound of Ammonia Sesquioxide of Osmium falls 

 down as a black powder. (Sample shown.) 



When this substance is heated after being dried, it decomposes 

 with a hissing noise, Nitrogen and aqueous vapours being evolved 

 and the Osmium becomes reduced to the metallic state with great 

 violence. An admixture of J Sal ammoniac assists in making 

 this decomposition less violent. (Ammonia Sesquioxide of Os- 

 mium, as well as pure Osmium shown.) 



This metal Osmium, which received its name from the Greek 

 ^Oa-jjbr} (smell) in consequence of the strong and peculiar smell 

 of its highest oxide, the osmic acid, has only of late been more 

 closely investigated through the researches of Deville and Debray. 

 They found its properties essentially different from former 

 observers. The specific gravity ranges from 21'3 to 21*4, is 

 therefore heavier than Iridium or Platinum (21 '15.) It is not 

 fusible, but at a very high temperature, by which Iridium fuses 

 and Platinum volatilizes, it is evaporated as osmic acid without 

 showing any fusion. If Osmium is heated in a graphite pot with 

 7 to 8 parts Tin to strong red heat, it dissolves in the Tin and 

 separates on cooling as a crystalline powder of great hardness, 

 which can be obtained after dissolving out the Tin with hydro- 

 chloric acid. The Osmium in its character very much resembles 

 Arsenic. It enters into combination with chlorine, as already 

 stated, forming protochloride and bichloride of Osmium, the 

 first having an olive green, the latter a red-brown colour. .The 

 solutions of these salts very rapidly decompose under separation 

 of Osmium and formation of H. Cl. 



The most interesting compound of Osmium is the Osmic acid 

 Os 4 . It is obtained when metallic osmium is heated in the 

 bulb of a glass tube, whilst oxygen gas passes slowly over it ; 

 the osmic acid thus produced is condensed in fine white needles 

 in the next glass bulb, which has to be kept well cooled, 

 (apparatus shown.) In this way I have prepared this specimen, 

 (osmic acid shown.) 



This Osmic acid fuses more easily than wax into an oily liquid. 

 It has an insupportably pungent odour, and its vapours attack the 



