522 Van Horn and Cook — New Occurrence of Pearceite. 



Percentage 

 found 



Atomic 

 weights 



Combining 

 weights 



Eatio 



Pro- Pro- 

 portion p'rt'n 

 found taken 



S 17-46 -=- 32-07 = -5444 

 As 7-56 74-96 = -1008 



Sb 0-00 



Ag 59-22-=-(107-88x2)= -2744 ) 

 Cu 15-65 ( 63'57X2)= -1231 j 



99-89 



= •5444 -4- -1008 =5-400X2 = 10-80= 11 

 = . J008 -=--1008 =1-000x2= 2-00= 2 



= -3975-f--1008 =3-943x2 = 7-886= 8 



The International Atomic Weights for 1911 were employed in 

 the calculations, and twice the atomic weights of silver and cop- 

 per were used on the basis that these elements are isomorphous 



Fig. 1. 



Fig. 1. Pearceite crystals from Veta Pica Mine, Sierra Mojada, Mexico. 



in the compound (Ag,Cu) 2 S. No antimony was found, so that 

 evidently the pure pearceite molecule is present, as was also 

 the case with the Montana occurrence mentioned at the begin- 



