256 Prof. 11. Bunsen on Rhodium, 



they are colourless ; the least excess oi iodide of palladium makes 

 them appear wine-red. 77 grammes of iodide of palladium were 

 obtained. 



A specimen of the precipitate left on ignition pure metallic 

 palladium, which dissolved readily and completely in nitric acid. 

 The whole of the iodine used in the precipitation may be readily 

 obtained in the form of chemically pure hydriodic acid, and be 

 used for fresh precipitations. For this purpose the iodide is in- 

 troduced into a tubulated retort, the neck of which is drawn out 

 and bent down at right angles, and is fitted into a flask close over a 

 layer of water. Into the tubulure is fitted a glass tube bound round 

 with asbestos and cemented by gypsum, through which a slow 

 current of hydrogen passes from a Dobereiner's apparatus to the 

 iodide placed on the bottom of the retort. The retort is heated 

 in a magnesia-bath (to be afterwards described) so strongly that 

 almost only hydriodic acid and very little free hydrogen emerges 

 from the drawn-out end. As the metal thus reduced retains 

 very small particles of subiodide of palladium with great persist- 

 ence, which render it partially insoluble in nitric acid, it must 

 be strongly heated once more in a current of hydrogen. 



The mother-liquor of this vermilion precipitate, which has 

 thus been worked up for platinum and palladium, may still con- 

 tain rhodium and iridium. It is evaporated to dryness with a 

 little iodide of potassium, whereby a mixture of iodide of rhodium 

 and iodide of iridium is separated ; this is dissolved in aqua regia, 

 and is separated by bisulphite of soda, as will afterwards be de- 

 scribed — or, still better, is mixed with the material to be after- 

 wards worked by this process. 



2. Separation of Ruthenium, and parting of Iridium and Rhodium, 



The residue, after treating with nitric acid a kilogramme of 

 material, weighed 0*4 kilogramme. The platinum-metals had 

 to be extracted in a form suitable for further operations. Hess's 

 method of extraction by fusion with zinc alone is very imperfect, 

 and attended with considerable loss. The following method, 

 which depends on the deportment of zinc and chloride of zinc, 

 is, I think, preferable to all others previously used. 



If a small piece of zinc be melted in a porcelain crucible over 

 a lamp, we know that it becomes covered with a coating of oxide. 

 If iridium or any of the platinum-metals be added, this coating 

 of oxide prevents any contact of the metal with the fused zinc, 

 even if the metal be dipped in ; but if a few grains of sal-am- 

 moniac be thrown on the fused zinc, ammonia, hydrogen, and 

 chloride of zinc are formed, and the latter at once dissolves the 

 layer of oxide with the formation of basic chloride. The zinc at 

 the same time closely resembles pure mercury in its lustre and 



