H. L. Wells — Sperrylite, a new Mineral. 69 



ing : when dropped on a red hot platinum foil it instantly 

 melts, gives off white fumes of arsenic trioxide having little or 

 no odor, and porous excrescences are formed on the platinum 

 which do not differ in color from the untouched foil. 



Chemical analysis. — The following analyses of the mineral 

 were made after a considerable amount of preliminary work 

 had been done on it, the results of which confirm these iigures. 



Ratio. 

 •550 = 2 



•274 = 1 



99-38 99-53 99-46 



The composition is consequently represented by the formula 

 PtAs,, a small portion of the platinum and arsenic being 

 replaced respectively by rhodium and antimony. In composi- 

 tion this mineral appears to be nearer Wohler's laurite* than 

 any other mineral now known. The form of both is isome- 

 tric,f but their composition is apparently not quite analogous 

 since the formula of laurite is given as RuSj+^Ri^Os. It 

 is possible that the latter formula is slightly incorrect since 

 Wohler used an extremely small quantity (-314:5 gram) for his 

 analysis and acknowledged the uncertainty of his results. It 

 is also to be noticed that the composition of the mineral cor- 

 responds to that of the artificial platinum arsenide made by 

 Murray.:}: The writer has confirmed the composition of this 

 artificial arsenide by heating a known weight of platinum to 

 redness and passing over it vapor of arsenic in a current of 

 hydrogen. The following are the results of the experiments : 





I. 



II. 



Mean. 







As 



40-91 



41 05 



40-98H 



- 75 = 



•546 



Sb 



0-42 



0-59 



0-50-; 



-122 = 



•004 



Pt 



52-53 



52-60 



52-57-= 



-197 = 



•267 



Rh 



0-75 



0-68 



0-72H 



-104 = 



•007 



Pd 



trace 



trace 



trace 







Fe 



0-08 



0-07 



0-07 







SnO, 



4.69 



4-54 



4-62 









Pt taken. 



As absorbed. 



Ratio. 

 Pt As 



I 



II 



III 



•3806 



•5725 



1-0657 



•2922 

 •4354 

 •8112 



1 : 2-02 

 1 : 2-00 

 1 : 2-00 



It was noticed in these experiments that the arsenic com- 

 bines with the platinum with incandescence and the alloy melts 

 even below a red heat after a part of the arsenic has been taken 

 up. At the end of the operation, however, the fused globule 

 solidifies, throws out peculiar, arborescent forms and the PtAs, 

 remains as a porous and very brittle mass which is neither 

 fused nor changed in composition when heated to bright red- 



* Ann. Ch. Pharm., cxxxix, 116. 



•f- See next article for crystalline form of Sperrylite. % Watt's Dictionary. 



