J20 On Palladium and Rhodium. [Ski>t. 



and rhodium. This shows that a portion of these last three metals 

 is precipitated by the iron in the state of oxide ; otherwise muriatic 

 acid would not have dissolved them. This seems to prove likewise 

 that these metals in precipitating combine with iron and copper, 

 and prevent them from being attacked by nitric acid, even when 

 employed in considerable quantity. 



1 next treated the precipitate with nitromuriatic acid composed of 

 the acids of commerce. A part only of the matter was dissolved. 

 There remained a considerable quantity upon which the acid had no 

 action, though I employed at least 12 parts of acid. 



Supposing that this acid was too weak to act with efficacy upon 

 this matter, I composed a very strong nitromuriatic acid, and 

 poured six parts of it upon one of the residue. The action was now 

 very violent, and the solution went on plentifully without the appli- 

 cation of heat, as was evident from the strong effervescence, the 

 escape of nitrous fumes in abundance, the elevation of the tempe- 

 rature, and the change in the colour of the liquid. Yet the whole 

 matter was not dissolved. There remained at least ^-th, though heat 

 had been applied for a long time. 



I therefore poured four more parts of the same nitromuriatic acid 

 on it. There was still solution ; but it was less than what took 

 place at first. I will leave this residue at present, but I shall return 

 to it hereafter. 



Though the matter thus treated three times successively with 

 nitromuriatic acid had been previously subjected to the action of 

 nitric and muriatic acids, each of the three nitromuriatic acid solu- 

 tions contained still copper and iron. This shows that these metals 

 precipitated in combination with platinum and the other metals 

 mixed with it. It was by this union that they were protected from 

 the action of the simple acids, and even of the first portions of the 

 nitromuriatic acid. 



I had already observed these phenomena in a preceding process j 

 but as I had calcined the precipitate so as to agglutinate the parts, 

 I considered that as the cause of the union which prevented the 

 solution of the iron and copper. But the preceding result shows 

 us that this union takes place at the instant of precipitation. The 

 great quantity of oxide of iron which precipitates along with the 

 platinum, palladium, and rhodium, is very remarkable. 



The three solutions of the precipitate were mixed together, and 

 evaporated to the consistence of a syrup, to get rid of the excess of 

 acid. Being then sufficiently diluted with water, it was precipitated 

 by sal ammoniac. A pure yellow ammonio-muriate of platinum fell 

 down. 



The liquid being evaporated anew almost to dryness, and the 

 residue being digested in water, left a granular salt of a red colour, 

 similar to the blossom of the pomegranate ; but little soluble in. 

 water, and composed chiefly of platinum. I shall state hereafter 

 the cause of its red colour. 



After this long but necessary preface, I shall state the method 



