On a native Arseniate of Lead, gi 



and exposed to a low red heat, weighed, whilst still warm, 

 40'8, which, according to the proportion of 33 : 100, esta- 

 bhshed by Mr. Chenevix, implies 13*46 of arsenic acid, 

 f' 5. The superfluous lead was now separated from the fluid 

 by sulphate of soda, and filtered off. Ammonia precipi- 

 tated a minule portion of flaky matter ; it weighed, after 

 ignition, 0*2 of a grain; it consisted of silica and oxide of 

 lead, and must be attributed tb the nitrate of lead employed. 



B. 



1. The yellowish white residuum (a) (A, §2.) was dis- 

 solved without efl'ervescencc iii nitric acid, except a minute 

 portion oF silica, whicn, afier ignition, = 0* 8, A white 

 heavy maUer Was thrown down from this solution, by 

 -liquid sulphate of soda. The clear decanted fluid was eva- 

 porated to a small volume, and sulphate ot soda produced 

 a further separation of white matter ; it was sulphate of lead, 

 which, after exposure to a low red heat, and weifrhed, 

 whilst warm, = 47'<5, whic4i, upon the supposition that 

 cue himdred parts of sulphate of lead contain 69*74 of lead 

 + 3*48 of oxyv::;en, is equivalent to 34*77 of oxide of lead, 



2. The fluid, now frted from lead, deposited, oai the affu- 

 sion of ^mmonia, a greenish matter, which, after ignition, 

 became red, and = 0*033 of a grain. It was oxide of iron. 



■ 1. One hundred grains of larger crystals, some of which 

 were liollow, aild the surfaces of which were slightly and 

 pdrtially covered with silky filametits, treated in the same 

 way yielded 95*283 of sulphate ot lead, equivalent to 6Q'7Q 

 *oF oxide, and 80 of arseniate of lead, which indicates 26*40 

 Vif arseiiic acid. The oxide of iron, in this case, amounted 

 *to only '05 of a grain, and the residuary silica was in too 

 small a quantity to be weighed. 



2. I have endeavoured to decompose this fossil by boiling 

 it to dryness in a solution of four times its weight of the 

 purest subcarbonate of potash, and exposing the dry mass, 

 for a very short time, to a low red heat ; but I found, that 

 only a part of the arsenic acid had united to the alkali ; the 

 larger portion of it was detected in the nitric solution of the 

 residuum ; but the relative proportions of the oxide and the 

 acid, were found to correspond almost exactly with the 

 foregoing statement of them. 



3. I found ako, that carboilafe of amrnonia precipitated' 

 jthis mineral^ in an unaltered slate, from its solution in 



nitric 



