Prof. Regnault on the Specific Heat of some Simple Bodies. 109 



Metals which accompany Platinum. 



I have had frequent occasion to determine the specific heat of 

 some of the metals which accompany platinum (Ann. de Chim. et 

 de P/ujs. 2nd series, vol. lxxiii. ; 3rd series, vol. xlvi.), but I had 

 doubts as to the purity of several of the specimens used. M. 

 Chapuis lent me, in June 1857, several specimens of rhodium, 

 osmium, and iridium, which he had prepared with the greatest 

 care by the methods described by him in the following Note : — 



1. The osmium was obtained by roasting osmium-iridium. 

 Osmic acid, condensed in a solution of caustic potash, was con- 

 verted into osmite of potash by alcohol, and then washed for a 

 long time with a solution of chloride of ammonium. The double 

 chloride of osmium and ammonium was heated in a current of 

 hydrogen, and the spongy osmium thus formed united by com- 

 pression into a single ingot. 



2. The iridium was obtained by heating with nitre the residues 

 of platinum-mineral previously freed from osmium. The product, 

 washed with water, was treated with aqua regia, and the liquors 

 precipitated with chloride of ammonium. The double salt was 

 calcined in a platinum crucible, the temperature being slowly 

 raised. The metallic mass was again washed with a solution of 

 sal-ammoniac, and then heated in the muffle; a considerable 

 quantity of osmium was given off. After these operations it 

 was found that the iridium still contained perceptible quantities 

 of platinum, palladium, and gold. It was again treated with 

 weak aqua regia ; and as the presence of foreign metals was still 

 apprehended, it was again fused with nitre, and the oxide thus 

 obtained treated with aqua regia. The evaporated liquors gave 

 well-defined crystals of the double chloride of iridium and potas- 

 sium : the double chloride was heated in a crucible with car- 

 bonate of soda, and the iridium thus obtained was compressed 

 into a single cylinder by percussion. 



3. The rhodium was extracted from the residues of the pre- 

 paration of iridium. These residues, exhausted by the treatment 

 with aqua regia, were mixed with fused salt and then heated to 

 redness in a current of dry chlorine. The substance was then 

 treated with boiling water, and the solution gave, on evaporation, 

 beautiful octahedral crystals of the double chloride of rhodium 

 and sodium. These crystals were redissolved in hot water, and 

 sal-ammoniac added ; on cooling, needle-shaped crystals of the 

 ammoniacal double chloride were deposited. This substance, 

 heated in a muffle, gave metallic rhodium. As some doubt still 

 remained of its purity, it was again treated with aqua regia, the 

 metallic residue again fused with common salt, and the mixture 

 heated in a current of dry chlorine. The substance was redis- 



