25fi ARSENIATED COPPER. 



Mineralogy is The mlncralogical fpecies are very accurately determined 



jiot yei f.ifh- ^^ ^i^g acrreernent or dilierence which exifts in the firfl: mole- 



ciently perfect •' . " . 



toadmitof the cuJic oF the formation of thedifferent fubfiances, but until wc 

 reparation of the \^^y^, (^-^ed data to appreciate, in a deternminate and invariable 

 Ipecies by the n , • , , , r . < . f 



form of the manner, all which relates to thele moleculag, the conftancy or 



primit ve mole- 4i,e drfF^rence in thefe exterior fpecific chdra6lers will always 

 be the only means within our power of uniting or feparating 

 the fpecies. I acknowledge, however, that in this cafe, it is 

 necelfary that this divifion fiiouid be eftabliftied as much as pof:. 

 fible on flriking and ellential charafters; and I agree, at the 

 fame time, that latterly, this method has perhaps been, much 

 abufed by giving importance to ilmple and cafual charadersj 

 this has frequently placed fubdances in the number of fpecies, 

 which thould only have been confidered as fimple varieties of 

 thofe already known. 



I fliall now beg of you. Sir, to compare with me thediffep- 

 ent fpecies of arfeniated copper which I have defcribed. 



Comparifon of the Firjl and Second Species. 



Cornparifon of The form of the firfi fpecies is an obtufe rectangular o6ta- 

 tte hi and hedron, whofe faces are unequally inclined. Two of them 



fecond fpecies of ' ~i J 



arfeniated cop- meet at the lummit under an angle of 139° and at the bafe 

 P"' under one of 50°. The two others meet at the fummit in an 



angle of 1 15'', and at the bafe in one of 65°. This octahe- 

 dron is ufually cuneiform: I have never perceived any modifi- 

 caiion of it. 



The form of the fecond fpecies is a hexahedral plate, always 

 very thin, whofe vertical planes are inclined alternately in op- 

 potite direflions, fo that two of them, on the fame fide, make 

 an angle of 133° with the terminal faces to which they incline, 

 and the third, one of 1 13°. 



The moft ufua! colour of the firft fpecies is a deep and very 

 brilliant fky-biue, which fometimes changes to green. 



That of the fecond fpecies is a fine emerald green : I have 

 never feen eny other. 



The fpecific gravity of the firtl fpecies is 2831 : that of th.c 

 fecond 25 1-8. 



The hardnefs of the firfl: is fuch that it readily cuts carbon- 

 ated lime: the fecond is no harder than is fufilcient to cat 

 gypfum. 



