THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



«^- — 



[THIRD SERIES.] 



SEPTEMBER 1850. 



XVIII. On the Composition of Beudantite. 

 By John Percy, M.D., F.R.S* 



LEVY first described this mineral, and from his own ex- 

 amination of its physical characters, and Wollaston's 

 determination of its composition, pronounced it to be a distinct 

 species. 



The following is Levy's description, the measurement of the 

 crystals being omitted. 



"This substance occurs in small crystals closely aggregated, 

 of which the form is a slightly obtuse rhombohedron, with the 

 summits truncated. Their colour is black at the surface, and 

 their lustre somewhat resinous; but their fragments are trans- 

 lucent, and of a deep brown colour. The hardness is sensibly 

 greater than that of fluate of lime. When pounded, the 

 colour is of a greenish-gray. The matrix seems to be the 

 same substance in an amorphous state with veins of fibrous 

 haematite ; it comes from Hornhausen on the Rhine. I am 

 indebted to Dr. Wollaston for the chemical examination of 

 this mineral, the result of which is very interesting; the only 

 substances he has been able to detect in it being oxide of lead 

 and oxide of iron." — Annals of Philos. N. S. vol. xi. p. 195. 



Recently, Descloizeaux has examined the crystallographic, 

 and Damour the chemical properties of Beudantite {Ann. de 

 C/i. et de Phys. t. x. p. 73, 3 ihme S.). The crystals upon 

 which they operated were taken from a specimen in the col- 

 lection of the Ecole des Mines at Paris, and were of two 

 kinds, green semi-transparent cubes, and bright black cubes, 

 as seen by reflected light. Damour asserts that the former 

 were composed of arsenic acid, oxide of iron and water, and 



* Communicated by the Author. 

 Phil Mag. S. 3. Vol. 37. No. 249. Sept. 1850. M 





