18M.] On Palladium and Rhodium. t\J 



it not only palladium, but likewise another metal, till then un- 

 known, to which he gave the name of rhodium, from the red 

 colour of some of its salts. He published an account of its prin- 

 cipal properties in the Philosophical Transactions for 1804. Dr. 

 Wollaston employed the following method to separate these two 

 metals from a solution of platinum. He dissolved in nitromuriatic 

 acid two ounces and a half of crude platina ; he precipitated the 

 platinum by means of sal ammoniac from a portion of that solution 

 corresponding to 1000 grains of the ore. Into the residual liquor 

 he put a plate of zinc, in order to precipitate from it all the metals 

 which it held in solution. But as he found both copper and lead 

 present, as well as palladium and rhodium, he separated them by 

 means of weak nitric acid, which does not act upon the two last 

 metals. 



He dissolved the residue in nitromuriatic acid, and precipitated the 

 platinum still remaining by means of sal ammoniac. To the solution 

 thus precipitated he added 20 grains of common salt, evaporated to 

 dryness, and washed the residual mass with alcohol till that liquid 

 came off colourless. By this method he dissolved the triple salt of 

 palladium, but left that of rhodium. 



Though Dr. Wollaston only operated on 1000 grains of the ore 

 of platinum, and of course had only six or seven grains of the new 

 metals at his disposal, yet he determined their principal properties, 

 which does infinite honour to his sagacity ; for the thing appears at 

 first view incredible. 



For my part, though I employed CO marcs (about 3!*£ troy 

 pounds) of crude platina, I found it very difficult to separate exactly 

 the palladium and rhodium from the platinum, and the other metals 

 which exist in that ore, and especially to obtain them in a state of 

 purity. 



II. 



Before describing the method which I followed to separate palla- 

 dium and rhodium in a state of purity from the ore of platinum, I 

 conceive it will be worth while to point out certain conditions 

 favourable to the solution of the ore of platinum, and to the preci- 

 pitation of that metal in the state of a triple salt. 



The first relates to the proportion of acids which ought to com- 

 pose the aqua regia. That which appeared to me the best is one 

 part of nitric acid and two parts of muriatic acid. Aqua regia thus 

 composed not only dissolves more platinum, but its price is nearlv 

 100 per cent, less than that of common aqua regia ; and when we 

 operate upon large quantities, this is a point by no means to be 

 overlooked. 



The second observation relates to the concentration of the acids. 

 The quantity of nitromuriatic acid necessary to dissolve platinum 

 decreases not merely in proportion to its concenl ration, but in a 

 much greater ratio; for example) if we suppose ;i volume of nitro- 

 uauri.uii: acid represented by two, to be capable of dissolving * 



