172 H. L. Wells — Note on Artificial Sperrylite. 



for 42*7 per cent of arsenic, and agreed within 0*8 per cent of 

 the theoretical amount. 



With the small quantity of the material received, the writer 

 has confirmed its composition qualitatively, and has found that 

 in appearance and pyrognostic properties it agrees precisely 

 with the natural substance. 



Professor Wm. E. Ford has kindly established the form of 

 the crystals by the following measurements, obtained from two 

 individuals : 



Cube on octahedron, meas.: 54° 34', 54° 49', 55° 5' ; calc: 74° 44'. 

 Cube on pyritohedron (210), meas.: 25° 40', 26° 31'; calc: 26° 34'. 

 Octahedron on pyritohedron (210), meas.: 39° 3', 39° 31'; calc: 

 39° 14'. 



A somewhat remarkable circumstance in connection with the 

 natural and artificial sperrylite is the fact that the crystals are 

 of similar size in both cases. Possibly the artificial crystals 

 may be slightly smaller, on the average, than those of the min- 

 eral from the Sudbury region, but the difference is not marked. 

 The natural crystals thus far found have always been very 

 minute — almost microscopic. Since the artificial crystals were 

 prepared on a rather small scale, while the mineral appears to 

 have been formed in massive sulphide ores, such a close agree- 

 ment in size, as well as in every other respect, would hardly 

 be expected. 



While the artificial compound PtAs 2 was prepared by the 

 writer by passing arsenic vapor over hot metallic platinum, 

 and the same compound had been made a long time previously 

 by Murray, no distinct crystals were thus formed, so that the 

 new product is of much interest and importance. 



Sheffield Laboratory, 

 New Haven, Conn., November, 1912. 



