188 



ON ARSENIATED COPPER. 



Mr. Chenevix was employed at the fame time on the ana- 

 lyfis of this fubftance. Soon after they both pubh'ftied the re- 

 fults of their refearches in the Philofophical Tranfadions* i 

 and Mr. Chenevix teftifies his admiration at fuch a perfect 

 agreement between two fciences which employ two methods 

 fo different to interrogate nature. M. de Bournon, on his part, 

 fays that the analyfes of Mr. Chenevix have given the moft 

 fatisfadlory fandtion to the divifion which he had himfelf made, 

 of the arfeniated copper into four diftind fpecies. 

 Defcripilon of Before going farther, it is neceflary to make known the va- 

 the vaiicties. rieties of arfeniated copper w hich I have been enabled to exa- 

 mine. I (hall confine myfelf to giving a defcription of them, 

 fuccin6t and independent of the laws to which the ftriidlure 

 of cryftals is fubmitted, the a6lual ftate of our knowledge on 

 this fubjedl only admitting of hypothetical views, of which I 

 (hall fpeak hereafter. 



1. Obtufe odtahedral arfeniated copper, (Plate IX. Fig. 2): 

 incidence of P on ;j, 50^^ 4'; of P' onj5', Gb'^ 8'; of P on P', 

 139** 47' f. The colour of the cryfials is fometimes a finece- 

 leftial blue, and fometimes a green, which varies between a 

 grals-green and a pale green. The odahedron fometimes be- 

 comes cuneiform, lengthening fo that the terminal edge is pa- 

 rallel at D. 



2. Lamelliform arfeniated copper. In hexagonal lamina?, 

 wbofe narrow faces are inclined alternately in contrary direc- 

 tions ; the incidence of two of the narrow faces, fituated on 

 the fame fide, on the correfpondent bafe, 135** nearly, ac- 

 cording to M. de Bournon : incidence of the third on the fame 

 bafe, 115® nearly. 



* For 1801, p. 199, etfeq: 



f I adopt here, very nearly, the refults of M. de Bournon, who 

 indicates 50' for the incidence of fxjn p, and 65' for that of P'on 

 /'. I have only endeavoured to find limits capable of facilitating 

 the calculations which I propofe to make. Let bac, gac, (Fig. 4) 

 be the fame faces as P and P, (Fig. 2) ; let «o (Fig. 4) be the 

 height of the pyramid which has its fummit in A^ (Fig. 2); on 

 (Fig. 4) a perpendicular to be, and or perpendicular to eg : — if ao 

 = ^^"588, o» r: •^2605, and or y'H^O, we fliall have 50° 4' for 

 the incidence of P on p (Fig. 2), and 65° 8' for that of P' on p't 

 whjcnce is deduced, by calculation, 139° 47' for that of P on P', 



The 



