254 M. Baruel on the Process 



salt to redness in a crucible, we decompose it, and the rhodium 

 remains pure and perfectly metallic. The second means of ob- 

 taining the rhodium from the above iquid, consists in plunging 

 into it plates of iron. The rhodium and the copper are preci- 

 pitated, carrying down with them a little iron. When every 

 thing is fallen down, the liquor is decanted, the precipitate is 

 washed, and boiled with an excess of strong muriatic acid, 

 which dissolves all the iron. The liquid is now poured off, the 

 residuum is washed with a sufficient quantity of water, and is 

 next boiled several times with concentrated nitric acid, which 

 dissolves all the copper. The rhodium being completely inso- 

 luble in each of these acids separately, remains under the form 

 of shining pellicles, which must be washed and dried. Rho- 

 dium being the most infusible of metals, cannot be melted but 

 in small pieces, by the aid of a flame fed with oxygen gas, or by 

 the compound flame of hydrogen and oxygen. (See Annotations 

 infra.) 



21. Let us return to the black powder separated from the 

 platinum ore, by treating it with nitro-muriatic acid. We have 

 said that this black powder was an alloy of osmium and iridium. 

 It is scarcely affected by any nitro-muriatic acid. It requires, 

 indeed, an enormous quantity of this acid to dissolve a minute 

 particle of it. The only means of attacking this alloy, is to cal- 

 cine it with nitrate of potash. With this view, we triturate the 

 black powder with twice its weight of a mixture of three parts 

 of nitre and one of caustic potash, and introduce the whole 

 into a silver crucible, which is to be kept at a cherry-red heat 

 for half an hour. In consequence of the affinity of the potash 

 for the oxides of osmium and iridium, the nitric acid of the 

 nitre is decomposed, and oxidizes these metals. The crucible 

 is to be withdrawn from the fire, allowed to cool, and cold water 

 is then poured on the materials. This dissolves the potash, the 

 whole oxide of osmium, and a little of the oxide of iridium. 

 The whole being thrown on a filter, the oxide of iridium remains 

 above, which is to be washed and dried. 



22, The filtered liquor which contains the combination of pot- 

 ash and oxide of osmium, as well as a little oxide of iridium, is 



