On a native Arseniate of Lead, 93 



mass of nitric acid produced its effect, and volatilized a 

 portion of the niuriatic. 



Another source of error I found in the following anoma- 

 lous circumstance, viz. a simultaneous precipitation of a 

 portion of arseniate of lead takes place with that of the mu- 

 riate of silver. Whatever combination this may be, it is a 

 weak one, and may be severed by nitric acid, which dis- 

 solves the arseniate and leaves the muriate ; or by ammonia, 

 which takes up the muriate, to the exclusion of the arseniate. 



The conclusion to which many experiments have led me 

 is this, that the muriate of silver produced in the nitric so- 

 lution of one hundred grains of arseniate of lead by nitrate 

 of silver, amounts to about 9'5. 



E. 



In order to prove that the acid, which is combined with 

 the oxide of lead in^ this mineral, is the arsenic acid, and 

 that it is not combined with phosphoric, I decomposed 

 some of its acid, which had been combined with lead in 

 ihe foregoing experiments, by means of sulphuric acid, and 

 filtered off the sulphate of lead. The fluid which passed 

 through the filter v\ as evaporated nearly to dryness, and it 

 assumed the appearance ot cryslalline grains. Some of it 

 was exposed to the flame of the blow-pipe in a gold spoon ; 

 at first it became like a white dry powder, which melted 

 before an increased heat : placed on charcoal and ignited, 

 ii was totally dissipated in arsenical fumes. 



Some of it was dissolved in water, and, dropped into 

 liquid sulphate of tilanium, a white precipitate was pro- 

 duced : combined with soda, it precipitated silver from. the 

 nitrate of silver, of a brick colour. It precipitated mer- 

 cury from its nitrate, of a yellowish colour, which after- 

 wards became reddish. This precipitate, exposed to the 

 flame of the blow-pipe on charcoal, exhibited the same 

 phcenomena as arseniate of mercury. 



I precipitated magnesia from its muriate, and redissolved 

 it by carbonate of ammonia, perfectly saturated with car- 

 bonic acid. I divided this liquid into two portions, and 

 dropped into both a solution of the combination of the acid 

 of this mineral and ,!^oda. No precipitate was produced. I 

 dropped into one of the vessels some liquid phosphate of 

 soda, and a separation of saline matter was instantly pro- 

 duced. I soon, however, found, that this mode of di- 

 stinguishing the phosphoric from the arsenic acid could not 

 be depended upon. For in the other vessel, in which no 

 phosphate of soda had been dropped, in a short lime, saline 



tufti 



