J94 ON ARSENIATE0 COPPER, 



But the incidence of /> on P givcf?, on the contrary, an acotc 

 angle of 50^. Now, let us imagine a decrement indicated by 

 ^D, which ads on the face p and on that which is oppofite ; the 

 faces produced will be fifuated vertically ; whence it follows 

 that that which will maf[< the face p will form an angle with P 

 equal to 90° plus 25°, which is the half of the inclination of ^ 

 to P, that is to fay, the angle in queftion will be 1 IS**, con- 

 formably to obfervation *. 

 Their diviiion I (hall not urge thefe refults farther, which, as I have already 



i^nof admitte" '^^^^^' ^ ''"'>' ''^'"" ^' P"'^'^ hypothetical ; and I fhall abftain 

 by the laws of f»"om adding my opinion with refped to the fourth of the fpe- 

 Arufturc, ^ies admitted by M. de Bournon, which, according to him, has 



the equilateral triangular prifm for a primitive form. It is 

 enough for me to have Qiown that, with refpecl to the divifion 

 of arfeniated copper into four diftind fpecies, the laws of the 

 flru6ture may give rife to doubts which deferve fome attention. 

 If they can be removed, as it is not impoffible they may, an- 

 other proof will be obtained in favour of an opinion on which 

 no obfcurity fliould remain, that it may be worthy of being una- 

 nimoufly adopted. 

 Comparlfon of If we now confider the refults of the analyfes which Mr. 

 Mr.cheneyix's Chenevix has made of the difFerent modifications of arfeniated 



analyfes and M. £j.iz-ri/-./- .^ 



deBournon'sdi- copper, we hnd, that in fuch of thefe analyfes as have had for 

 vifion. their objeft the types of the four fpecies admitted by M. de 



Bournon, three have given fenfible differences in the relative 

 quantities of copper, arfenic acid, and water. Thefe analyfes 

 correfpond with the firft, third, and fourth fpecies. Another 

 analyfis, made on the fecond fpecies, gave only copper and 

 arfenic acid, without water. Thus, fuppofing that the rela- 

 tions between the quantities of the three principles contained 

 in the modifications which Mr. Chenevix calls arfeniates of 

 hidrate of copper, conftitute true limits, and thatj in the mo- 

 dification which he calls fimply arfeniate of copper, the abfence 

 of water depends on the nature of the fubfiance itfelf,. we 

 niall, in this refped, find an agreement between the refults of 



* I have a lamelliform cryftal, on which, inftead of a fimple 

 bevil, there are two, fituated in contrar)- direaions on the fides of 

 the fame edge ; but they are too Imall for it to be pofllble to deter- 

 mine the polltions exa(5l]y. 



* analyfis 



