NATIVE ARSENIATE OF LEAD. gQ>^ 



«Sropped into both a solution of the combination of the acid acid from the 

 of this mineral and soda. 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 dis- 

 tinguishing the phosphoric from the arsenic acid could not 

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

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

 tufts made their appearanee, and an abundant deposition of 

 saline matter was formed. I found also, that if the solutioa 

 had been more concentrated, the precipitation would have 

 immediately taken place. 



On making a comparative experiment with arsenic acid, I 

 found, that it forms a triple salt with ammonia and mag- 

 nesia, analogous to the phosphoric salt described by Dr. 

 Wollaston. The figure of the arsenical salt, as far as I 

 could determine it from a confused crystallization, is a 

 triedral prism. 



We are therefore, I think, authorized from the experi- 

 ments herein detailed, to conclude, that the fossil, which 

 is the subject of this paper, is arseniate of lead, and that, 

 if we state that the relative proportion of the constituent 

 parts of it are in one hundred as follows, we shall not be 

 far from the truth : 



Oxide of lead - - 69-76 Component 



parts or the 

 Arsenic acid • - - 26*40 mLneraL 



Muriatic acid - - 1*58 



The silica and the oxide of iron, which account for a 

 portion of the loss; and the alumina and copper, which 

 are sometimes found in an analysis of this fossil; I do not 

 conceive to be essential to it. 



The existence of a minute portion of muriatic acid as a Curious fact, 

 constant ingredient of it is a curious fact : and it is still more 

 curious, when we consider it in connexion with the analogy, 

 that in this particular it maintains with the natural phos- 

 phates of lead. 



IX. EoopeiimenU 



