5 60 Intelligence and Miscellaneous Articles. 



attacked by its weight of nitrate of barium and four times its weight 

 of baryta, or else by five times its weight of binoxide of barium in 

 a crucible of silver or porcelain. The material, pounded, mixed 

 with four or five times its weight of water, is treated with a cur- 

 rent of chlorine in a tubulated retort with an emery stopper. When 

 it is supersaturated with chlorine, it is distilled in a very slow cur- 

 rent of that gas. Volatile hyperruthenic acid is obtained, which 

 passes at first in red crystals or minute drops, which afterwards 

 dissolve in the water proceeding from the distillation. The iridiate 

 of barium is transformed into green perchloride of iridium and 

 chloride of barium, with disengagement of oxygen. The liquor de- 

 prived of baryta by titrated sulphuric acid, is evaporated to dryness 

 to separate the silica. The residue, taken up by water, consists of 

 red-brown bichloride of iridium, the green chloride having lost some 

 chlorine during the evaporation. We precipitate it by sal ammo- 

 niac, and wash for a long time with a semisaturated sal-ammoniac 

 solution the deep-violet chloro-iridiate of ammonia, which we after- 

 wards calcine in a current of hydrogen, and thus obtain metallic 

 iridium. This, treated with nitre and potash in a gold or silver 

 vessel, gives a violaceous mass which, taken up by water, colours 

 it violet or deep blue. The residue is washed successively with 

 water, dilute hydrochlorate of ammonium (which removes the 

 potass), oxalic acid (to dissolve the iron), chlorinated water, and, 

 finally, ammonia to take up the gold or silver*. 



The iridium, strongly calcined in a crucible of charcoal purified 

 by chlorine, is afterwards fused in pure lime with the precautions 

 indicated for platinum ; only pure dry hydrogen must be substi- 

 tuted for illuminating-gas. 



Densities. (1) Pure Platinum. — To arrive at the determination of 

 its density, we fused our ingots again a great many times, always 

 obtaining numbers close to 21*5 when the ingots presented the 

 proper appearance. "We here give the details of the experiment 

 which gave the highest density : — 



Weight of the platinum in air at 17° ] OA , 1/n 



and 764 miffims j 204 - 141 S«™™s. 



Loss of weight in water at 17°*6 9*498 „ 



Density (uncorrected)t 21*504 



Other experiments gave numbers between the limits 21*48 and 



21*50. The metal did not contain impurities in sensible quantity. 



When the ingots are rolled, their density is diminished. This is 



* If a silver vessel is used, or the presence of rhodium is suspected, the 

 reduced material must be again attacked with bisulphate of potass, and 

 then with nitric acid and ammonia. 



t To obtain D the density at zero, the density D* must be introduced 

 in the formula 



n _(D,+0-001)(l+to) 



in which k is the coefficient of dilatation of the metal, and V; the volume 

 of water, at the temperature of the experiment. 



