NATIVE ARSENIATE OF LEAD. $Q^ 



S I found also, that carbonate of ammonia precipitated Analysis. 

 this mineral, in an unaltered state^ from its solution in 

 nitric acid; as no arsenic acid had united with the precipitant. 

 The solution of the nitrate of ammonia was evaporated to 

 dryness, and exposed to ared heat in a platina crucible ; but 

 nothing was left, except a slight trace of oxide of lead. 

 We may infer from this the at>scnce of both the fixed 

 alkalis. 



4. I found in one specimen only of this fossil any notable Variety, 

 difference in the relative proportions of the oxide of lead and 

 of the acid, to which it is united. It consisted of crystals 

 confusedly matted together in a more compact mass, than 

 this fossil generally assumes. One hundred grains were 

 dissolved in nitric acid ; the marine acid was separated by 

 Bitrate of silver, and any redundant silver hy muriate of 

 ammonia. The lead was separated by sulphuric acid, and 

 i\ie superfluous portion of that acid by nitrate of barytes, 

 and the arsenic acid was combined with oxide of lead by the 

 affusion of nitrate of lead. The muriate of silver = 9*8; 

 the sulphate of lead = 97*6, and the arseniate of lead = 72, 

 equivalent to 1'63 of muriatic acid, 71'46 of oxide of lead, 

 and 23'88 of arsenic acid, respectively. The quartz = 0^35, 

 and the oxide of iron 02 nearly. 



Another portion taken from the same specimen, treated 

 with an alkali, gave very nearly a similar result. 



D. It will now be necessary for me to speak concerning Nitrate of silver 

 an ingredient of this fossil, which I may have seemed to ^^ ^. ^^^^°^ °'^" 

 overlook. I mean the muriatic acid: I have found some varied in the 

 difficulty in ascertaining the proportion, which it bears to l^^'^'^'^y it m- 



^ & 1 1 •) , 1 T (licatcs. 



die other constituent parts, and from a cause, which I did 



not suspect. I considered, that the only sure mode of de- 

 termining this point was to have recourse to nitrate of silver, 

 which might effect a direct separation of the marine acid 

 from the nitric solution of this fossil. But I found, in 

 many experiments upon given quantities of this mineral, 

 that the results, wliich I derived from this most valuable 

 chemical test, were variable and uncertain. 



At last, I was enabled to trace the errourand uncertainty 1st source of 

 np to two sources. In the first place, I found that the"'^^"'"- 

 muriate of silver was more abundant ia the cases, where I 



employed 



