9iS6 Royal Socutj of 'London. 



fourth. As the quanlity of this metal diniinifhes, the fpecific 

 gravity incrcafes; the dudility is lefs ; and after 12*5 it be- 

 gins to be no longer a<5lcd upon by nitric acid. 



Mr. Chencvix gives many methods for preparing a fub- 

 ftance fimilar to palladnnii ; but the following is the leaft 

 liable to fail : — Take a certain quantity of platina, reduced 

 from the triple ammoniacal fait, and diffolve it in nilro-mu- 

 riatic acid : add fomething more than twice the weight of 

 the platina of red oxide of mercury, and take particidar care 

 to faturate all excefs of acid : then pour it into a folution, alfo 

 faturated, of green fulnhate of iron; heat the mixture, and 

 a black precipitate will be formed after fome time. This pre- 

 cipitate vveiiihs rather more than two and a half the original 

 quantity of the platina; but, expofcd to a red heat, a part of 

 the mercury is volatilized. Fufed at a ftrongcr heat, it yields 

 a metallic button, which in diiferent experiments gives a dif- 

 ferent fpecific gravity. This experiment it: of a very delicate 

 nature, and does not always fucceed ; and Mr. Chenevix 

 recommends perfeverance and repeated trials to all who would 

 form palladium. It is not often to be obtained of the exa6l 

 fpecific gravity announced by the author of the fraudulent 

 advertifement ; and the fpecific gravity is not conftantly the 

 fame in all his fpecimens. The difficulty is, to unite a fuffi- 

 cientlv large portion of mercury with the platina to produce 

 perfect palladmm. It may be obtained by this method as 

 low as iO'5, fometiines as high as \^. Mr. Chenevix men- 

 tions fome methods of combining platina and mercury in the 

 dry way, fuch as count Mudiin Pulkin's amalgam fufing with 

 cinnabar, lime, and borax; &c. 



He then relates fome experiments upon platina ; upon its 

 oxides, which are two, viz. one of 7 the other of J3 per cent, 

 of oxvcen; upon the affinities of the oxide for the acid and 

 aromatic falts formed by them. He gives numerous exam- 

 ples of the affinities of metals for each other ; and of anoma- 

 lous precipitations, when two or more metals are prefent in 

 the fame Iblution. He fays, that the fixation of mercury by 

 platina, together with other fatts related in this paper, will 

 tend to make us particularly cautious in pronouncmg upon 

 difcoveries of fuppofcd new metals, and promote fccplicifm 

 even upon our prelenl knowledge. He adduces inftances ot 

 the ditference that exifts between a folution of platina and a 

 folution of mercury merely mixed, and a folution of thefe 

 metals after they have been united. In the former cafe they 

 are eafily feparalcd ; in the latter there is no method of com- 

 pletely difuniting them. He concludes with a curious (late- 

 jnenl of the approximation of fevcrai metals and of feveral 

 earths to each other m their chemical properties, which tol- 

 7 low 



