for procuring pure Platinum. 205 



put into a flask, and saturated with nitric acid. The liquid is 

 then put into a retort, to which is fitted a tubulated globe, sur- 

 rounded with moistened cloths. On distilling, the water which 

 rises in vapour carries with it all the oxide of osmium. When 

 the liquid is two-thirds drawn over, the whole osmium is usually 

 volatilized. The liquid remaining in the retort contains the ni- 

 trate of potash, and a trace of iridium. The aqueous solution 

 of osmium is as colourless and limpid as distilled water. It has 

 a strong and peculiar odour, extremely irritating to tlie nostrils, 

 and which it is dangerous to inhale for any length of time. In 

 order to obtain the osmium from this solution, it is put into a 

 matrass, and we add a little muriatic acid to acidulate it slightly, 

 and then insert a plate of pure zinc. The oxide of osmium is 

 decomposed by the zinc, which is dissolved in the muriatic acid, 

 and the osmium is precipitated to the bottom of the liquor in 

 the form of a blackish-blue powder. When the oxide of osmium 

 is completely decomposed, which may be recognised by the 

 liquid losing its odour, we decant the fluid, pour the powder of 

 osmium on a filter, wash it copiously with water, dry it, and 

 put it immediately up in a well-stopped phial. 



23. The oxide of iridium, proceeding from the calcination of 

 the black powder with nitre and potash, which remained on 

 the filter, is by no means pure. It is a mixture of oxide of 

 iridium, of a certain quantity of the black powder, or alloy of 

 osmium and iridium, which has not been affected by the nitre, 

 and a little oxide of silver, derived from the crucible. This 

 mixture is to be treated with nitro-muriatic acid, which dis- 

 solves only the oxide of iridium, converts the oxide of silver 

 into a chloride, and does not act on the alloy. We next filter 

 and wash. The unattacked alloy, and the chloride of silver, 

 remain on the filter. This residuum is to be washed with water 

 containing a little ammonia, which dissolves the chloride of 

 silver, while the alloy of osmium and iridium remains pure. 

 This may be again calcined with the mixture of nitre and pot- 

 ash, to decompose it completely. 



24. Into the solution of iridium, which is of a very deep red- 

 dish-brown colour, muriate of ammonia is to be poured, and tlie 



