IRIDIUM. 689 



nant to contain these metals (Phil. Trans. 1804). The same 

 alloy occurs in flat white metallic grains in native platinum. 

 Iridium has also been observed in combination with about 20 

 per cent of platinum, crystallized in octohedrons, which are 

 whiter than platinum, and are said to have a greater density, 

 namely 22.6*6. Osmium and iridium are separated from each 

 other, with considerable difficulty, by processes for which I 

 must refer to the memoir of Wollaston (Phil. Trans. 1829, p. 8), 

 or to Berzelius, (Traite, t. I, p. 415). 



Iridium is obtained immediately from the chloride, by decom- 

 posing that salt with hydrogen at a gentle heat, or by exposing 

 it alone to a very high temperature, in the form of a grey me- 

 tallic powder, much resembling spongy platinum. It is one of 

 the most refractory bodies known, not being fused by the oxi- 

 hydrogen blow pipe. Mr. Children, however, succeeded in 

 fusing a portion of iridium into a globule, by the discharge of a 

 very large voltaic battery. This globule was white and very 

 brilliant, but still a little porous : its density was 18.68. Iri- 

 dium becomes white and brilliant by strong ignition, without 

 fusion, and is afterwards insoluble in acids. If reduced by hy- 

 drogen at a low temperature, it oxidates slowly when heated to 

 redness, or when digested in aqua regia. This metal is gene- 

 rally rendered soluble by one or other of the following operations. 

 It is calcined with hydrate of potash or nitre, or with a mixture 

 of these salts, which gives a compound of deutoxide of iridium 

 and potash. Or, the metal is reduced to a fine powder and in- 

 timately mixed with an equal weight of chloride of potassium or 

 sodium, and the mixture heated to low redness in a stream of 

 chlorine gas. The metal then combines with chlorine, and the 

 double chloride of iridium and potassium or sodium is formed, 

 which is soluble in water. 



Oxides of iridium. Iridium forms four compounds with oxy- 

 gen, which are obtained by decomposing the corresponding 

 chlorides. The protoxide of iridium, Ir O, is obtained from 

 the chloride produced when iridium is heated in chlorine gas. 

 Also by precipitating the double chloride of iridium and potas- 

 sium (KCl + lrCl) by carbonate of potash. The hydrate is 

 then obtained of a greenish grey colour, which is soluble in an 

 excess of the alkaline carbonate. This oxide is the base of a 

 class of salts. The deutoxide of iridium, Ir 2 O 3 , is formed 

 when the metal is calcined with hydrate of potash or nitre, and 



Y V 2 



