ARSENlAtED COPFER. 259 



This fubftarice very readily changes; it then pafTes (o an Reafons for 

 adi-grey, and lofes conficierably of its hardnefs: it alfo fre- ["'^'j'j'^S a fifth 

 quently experiences a more advanced decompofition, and then 

 becomes perKedly white, and (o Ml that the nail is iufficient 

 to cut it and (eparate its fibres. IF the mamellae which have 

 JjalFed to this Rate are broken, their decompofition is frequently 

 found to hjive reached their centre; but very frequently alfo 

 the centre has perfectly retained its brown colour and its hard- 

 hefs, and both are obferved to diminifli gradually on approach- 

 ing the circumference; if in this cafe the attention is dire<5led 

 to the fibres near the circumference, it will be feen that tiiey 

 are detached from each other, and that the furface itfelf o£ 

 thefe mamellae has the appearance of that of madrepore, from 

 the immenfe number of fifTures in different diref^ions, which 

 are occafioned by the contraftion. At length this fubfiance 

 arrives at fuch it degree of decompofition, that the mamella5 

 open completely, their fibres are entirely feparated from each 

 other, and, in this ftate, frequently become fo (lender and 

 flexible as perfe611y to refemble fmall portions of papyraceous 

 amianthus. 



Such, Sir, is the nature of the arfeniated copper, in which 

 t believe I have found properties and a mode of exiflence which 

 difl^er from thofeof the others, and which I have had opportu- 

 flities of examining with greater facility and accuracy fince the 

 Jmpreflion of my memoir. Tliis eafy decompofition, the pro- 

 drgious contraction, and the great change which this fubtiance 

 experiences in itfelf, have led me to fuppofe that the lofs of 

 water has great influence on it. But this fa6t is, however^ 

 rothing more than an opiniofi, which experience will either re- 

 jed or confirm; and I have fo ftated it. It may alfo be very 

 poilible that this arfeniate is no more than a variety of the third 

 fpecies, as f at fiift conikiered if. You muR, however, ac- 

 know'ledge that it offers very fingular charadlers, of which it 

 would, therefore, be interefting to know the caufe. 



The dealers in minerals from London, and principally Mr, 

 Mawe, have, 1 believe, taken a collec'^ion of arfeniated cop- 

 per to Paris. This fubfia,nce appears to me worthy of engag- 

 ing the attention of chemtfts who, I am of Opinion, fiiould 

 repeat the analyfes of it. Perhaps they may one day throw a 

 clearer light on a fittftance which has greatly interefted me, 

 and to which I am at this moment indebted for the pleafure of 

 having entered with you, Sir^ into a difcuffion, agreeable in its 

 manner and inftructive in its eflt6l. 



82 Frdfept 



