34 JMeinoir upon Palladium and Uhodium. 



tioii, but in a much larger ratio. Thus, I sup])Ose tliat iu a- 

 volume of aqua regia represented by two, there is enough of 

 acid for dissolving a given quantity of platina : this quantity of 

 acid reduced to half its volume, for instance, vvill then be uiuch 

 more than sufficient for producing the same effect. 



Thus an aqua regia composed of two parts of muriatic acid 

 at 22°, and one part of nitric acid at 34°, and which shall mark 

 about 25^ in the areometer, will only dissolve about one-eighth 

 of its weight of platina: whereas the aqua regia composed of 

 the same proportions of muriatic acid at 22", and nitric acid at 

 44% and which shall mark 2S° and a half in the areometer, will 

 dissolve one-fourth of its weight of piatina. It ivill therefore 

 recpiire one half less of this last to dissolve the same quantity of 

 platina ; now one part of this acid costs less than two of the 

 other. There is also this advantage, that the solution takes 

 place much more speedily, and almost without the assistance of 

 any other heat than that which is naturally developed during 

 the oj)eration. 



We may easily conceive the reason for what is above set 

 forth, when I observe that nitro-muriatic acid at 18^ or 20' 

 only vvill not attack crude platina at all, and will attack it but 

 very slowly even at a boiling heat : now at this temperature a 

 great part of the acid will be volatilized previous to acting upon 

 the platina. This is the reason why the acid which we collect 

 during the solution of the platina, even when reduced to the 

 consistence of a thick syrup, does not attack the ])latina again : 

 this is also the reason why we mav with \\eak aqua regia dis- 

 solve gold mixed with platina, without the latter being attacked - 

 at all. 



The third condition has for its object the state in which the 

 solution of platina ought to be put, in order to be more com- 

 pletely precipitated by sal ammonia. It must be sufficiently 

 reduced by evaporation, in order to congeal into a crystalHne 

 mass upon cooling ; for, if there remains too great a quantity 

 of acid, it retains much more triple salt in solution after mu- 

 riate of ammonia has been added. In fact, if in a similar solu- 

 tion which precipitates no more by sal ammoniac, we ~put any 

 alkali in order to saturate a part of the superabundant acid 

 which it contains, we see a new quantity of salt precipitated: 

 we know also that the ammoniacal muriate of platina is dissolved 

 more abundantly in water sharpened with nitro-muriatic acid, 

 than in pure water. I ascertained this fact, by putting into the 

 liquors from which the ammoniacal muriate of platina had been 

 separated, some pieces of iron, in order to precipitate the metals 

 which exist in the ore of platina. The first effect produced was 

 the precipitation of a considerable quantity of triple salt of pla- 

 tina 



