1835.] Improvements in Science . 119 



deep brownish red solution of double salt of iridium is 

 formed. The liquid after standing should be decanted 

 from the residue, which consists of iserine, and some pieces 

 of osmium and iridium. The fluid drawn off is distilled 

 to separate the oxide of osmium, which may still exist in it. 

 When the whole of the acid has passed over, the distillation 

 is stopped and the solution filtered. It is then to be eva- 

 porated over a fire, and during the concentration, carbonate 

 of soda is to be added in excess, which throws down a 

 blueish black precipitate. 



The dried black mass will then be strongly heated in a 

 Hessian crucible, and after cooling, be digested in water. 

 The residue is a sesquioxide of iridium. The filtered salt 

 solution contains, besides common salt and carbonate of 

 soda, also chromate of soda, which gives it a yellow colour. 



The sesquioxide of iridium contains, besides osmium, some 

 oxide of iron. It is to be placed in a glass tube, and hydro- 

 gen passed over it at a red heat till water ceases to be 

 formed. Metallic iridium thus obtained is a black powder. 

 It contains much caustic soda, which was chemically com- 

 bined with sesquioxide, and is now taken up by water. 

 By digestion in muriatic acid the iron is removed. After 

 washing, it may be placed between layers of filtering paper, 

 and pressed for several hours with a screw press. Heated 

 then in a crucible, it is obtained in the form of a firm polished 

 grey mass. Metallic iridium may be obtained by a shorter 

 method, but not In such purity; by evaporating the solution 

 of sodium chloride of iridium to dryness, heating to redness, 

 so as to melt the salt, and begin to volatilize the chloride of 

 sodium. The iridium will thus be reduced, and remain, 

 after digestion in water, as a grey or black metallic powder. 



Use of Iridium in the manufacture of Porcelain. (Pogg. 

 xxxi.) — The substances hitherto employed for painting 

 porcelain consisted of combinations of oxide of iron and 

 oxide of cobalt, the former producing grey and Indian ink 

 tints, and the latter the brown or blueish hues. It has been 

 lately ascertained, however, that iridium and rhodium 

 communicate to porcelain grey and black tints. The black 

 colour of iridium is very deep and pure, while its grey tint 

 is complete, without any tendency to blue or brown. The 

 residue from the Russian platinum mint contains iridium, 



