120 ON PALLADIUM. 



3dly. It IS more ufual for the prifm to have eight fides' 

 by truncation of each of its angles, and at eaeh extremity 

 eight additional furfaces occupying the place of the eight 

 hnear angles between the prifm and terminating pyramid of 

 Uie fecond variety. The complete cryftal has then thirty-two 

 fides. 



4.lhlv, The eight furfaces lafl mentioned, as interpofed 

 between the prifm and pyramid, are fometimes elongated into 

 a complete acute pyramid having eiglu fides arifing from the 

 angles of an odahedral prifm. 

 which prove the The third form above defcribed, correfponds fo entirely with 

 r.acurc oi the ^j^^j given by the Abbe Haiiy * as one of the forms of the 

 hyacinlh or jargon, that I have iiltle reafon to regret my inabi- 

 lity to obtain chemical evidence of the compofition of thele 

 cryftals. 



Thofe, and other impurities, I ufually feparated, as far as 

 was praflicabie, by mechanical means, previoufly to forming 

 the foluiion of piatina, which has been the principal object 

 of my attention. 



§ III. Preclpitalion of Piatina. 



Account of the When a confiderable quantity of the ore has been dif- 

 treatmentofpla- folved, and I had obtained, in the form of a yellow triple 

 iirftrrecipitdtion ^^'^ ^^ much of the piatina as could be precipitated by fal 

 of it by fal am- ammoniac, clean bars of iron were next imnierfed in the fo- 

 ther'poltion*was '"^•'^" ''^^ ^^^ purpofe of precipitating the remainder of the 



thrown down by piatina. 



II""* . „ , For difiindion it will be convenient to call this, which 



This 13 called _ . _ • ' ^ ^ 



the firft metallic in fad confifts of various metals, the firft metallic precipitate. 

 v'a"'''''-n dif^"'^ The treatment of this precipitate differed in no refped from 

 folved as the firft ^^I^^t of the original ore. It was dilTolved as before, and a 

 ore had been, portion of piatina precipitated by fal ammoniac; but it was 

 jiid again preci- iriii,i ... r r ^ 



pitatcd by fal ODlervable that the precipitate now obtained was not ot lo palo 



an.moaiac, a yellow as the preceding. Neverthelefs the impurity was in 



fo fmall quantity, that the piatina reduced from it by heat did 

 not diOer difcernibly from that obtained from the pureft yellow 

 precipitate. 



* Traite de Mineralogie, Pl. XLI. fig. 17. ^ourn. des Mines, 

 No. 26, fig. 9. 



At 



