466 



Mr. G. Matthey. On the Preparation of the [Apr. 3, 



on evaporation) to redness, at which heat it is reduced to the metallic 

 condition, the rhodium salt remaining undecomposed. 



By the method above described the platinum is freed not only from 

 rhodium, but from all other metals with which it may have been con- 

 taminated, and is brought to a state of absolute purity, of the density 

 21 '46, the highest degree obtainable. 



Iridium. 



In the preparation of this metal when intended to be used for the 

 manufacture of iridio-platinum alloy, I have arrived at freeing it to 

 the utmost possible extent from all its associate metals, except plati- 

 num, disregarding the presence of the latter ; the proportion of which, 

 once determined, would only form matter of calculation in the final 

 operation of mixing my alloy. 



In practice, the purest iridium which can be obtained from its 

 ordinary solution (deprived of osmium by long boiling in aqua regia 

 and precipitated by chloride of ammonium) will almost invariably 

 contain traces of platinum, rhodium, ruthenium, and iron. 



I fuse such iridium in a fine state of division with ten times its 

 weight of lead, keeping it in a molten state for some hours, dissolve 

 out the lead with nitric acid, subject the residue to a prolonged 

 digestion in aqua regia, and obtain a crystalline mass composed of 

 iridium, rhodium, ruthenium, and iron, in a condition suitable for my 

 further treatment. By fusion at a high temperature with an ad- 

 mixture of bi-sulphate of potash, the rhodium is almost entirely removed, 

 any remaining trace being taken up together with the iron in a later 

 operation. The iridium so far prepared is melted with ten times its 

 weight of dry caustic potash, and three times its weight of nitre, in a 

 gold pan or crucible ; the process being prolonged for a considerable 

 time to effect the complete transformation of the material into iridiate 

 and ruthenate of potash, and the oxidation of the iron ; when cold, 

 the mixture is treated with cold distilled water. The iridiate of 

 potash of a blue tinge will remain as a deposit almost insoluble in* 

 water, more especially if slightly alkaline, and also the oxide of iron. 



This precipitate must be well washed with water charged with a 

 little potash and hypochlorite of soda until the washings are no longer 

 coloured, and then several times with distilled water. 



The blue powder is then mixed with water strongly charged with 

 hypochlorite of soda, and allowed to remain" for a time cold, then 

 warmed in a distilling vessel, and finally brought up to boiling point 

 until the distillate no longer colours red, weak alcohol acidulated with 

 hydrochloric acid. 



The residue is again heated with nitre and potash water charged 

 with hypochlorite of soda and chlorine, until the last trace of 

 ruthenium has disappeared. 



