w-i^tonthc It is moreover well known^ that there Is a ftrong affinity 



piatina} between potafh and the ojiide of platina, and alfo that when' 



thofe fiibftances'are brought together in folulion, ^'triple fait, 

 ' but little foluble, is the refult. It was to avoid thefci difficulties 



that I had employed uncombined fulphuretted hidrogen gas; for 

 the method adopted by MefT. Rofe and Gehlen appearing to me 

 to be the application of two divellent forces, I prefumed that it 

 would produce a feparatfon. The refult of their experiment, 

 which, it appears from their paper, they had not anticipated, 

 — wouWhavean (hews the neceffity of the precaution I had ufed. The opera- 

 pofite "o That of' ^^^ which they performed to unite platina and mercury was, 

 the author's Jn fa6l, nearly the reverfe of that which they fuppofed they 

 proce s. ^^^ repeated from me, and might have been applied perhaps 



with a better profpecl of fuccefs towards the decompofition of 

 palladium. ^, 



They could not ' Meif. Rofe arid feehlen feem, in many parts of their paper, 

 fufe platina. j^ queftioh my having fufed platina; and inform us that aU 

 though they had expofed this metal in the furnace of the Royal 

 Porcelain Manufa6lory of Berlin, in which Wedgewood's py. 

 rometer ceafed to mark the degree of heat, they could not 

 accomplifh its fulion. Many of my friends in England hav6 

 however feen the buttons which I obtained, and which were 

 The author ufed not few in number. The flux which I had ufed was borax, 

 borax. But no mention is made in ar^y cne of the operations of MefT. 



.,j^ Rofe and Gehlen of borax having been employed. 



Particular ac- ]n many of their attempts they obiained an irregular and 



count of his porous mafs, which of courfe was of a fpecific gravity much in- 

 ferior to that of platina; and it might be inferred from their paper 

 that the diminution of fpecific gravity, which I had obferved, 

 was owing to the fame caufe. It is true, not only that I had 

 very often obtained fuch a mafs, but that I had frequently alfo 

 obferved no diminution whatfoever in the fpecific gravity of 

 the button which refulted from my operations. But all thofe 

 upon which I had founded ihe conclufions alluded to by MefT. 

 Rofe and Gehlen were' performed in the following manner, 

 AHe.Tiancru- and have been repeated fmce. A Heffian crucible was filled 

 c:b!e was lined y^\i\^ lamp-black, and thecontents prelfed hard together. The 

 with l-"^P^^*«^5iamp.black was then hollowed out to the (liape of the crucible 

 as far as one-third from the bottom, leaving that much filled 

 with the compreOTed materials ; this linings which adhered 

 firongly to the fides of the crucible, was made extremely thin, 



in 



