324 Mr. Ivory's Remarks on M. Poissoii's Memoir. 



I have taken for granted, from the general account given 

 by Klaproth of the yellow phosphate which he examined, and 

 of its locality, that it was the same mineral as that of which I 

 have now been giving an account, thouoh he calls its colour 

 citron yellow, and though his description of its crystalline 

 character is defective ; for in the more perfect specimens the 

 form of the crystal is a regular six-sided prism. It is not to 

 be wondered that he should have overlooked the chrome, — a 

 substance of which, when he made his analysis, nothing I be- 

 lieve was yet known, and which is here present in a very mi- 

 nute proportion ; not more, if my experiments are correct, 

 than between five- and six-tenths of a grain of the protoxide 

 in a hundred of the muieral. 



The amount of oxide of lead which Klaproth found, and 

 with which my analysis nearly agrees, was eighty per cent. If 

 from this the proper deduction be made for the chloride of 

 lead calculated from his statement of the muriatic acid which 

 the mineral contains, and also fo.r the chromate of lead which 

 1 have found in it, the phosphoric acid which corresponds with 

 the remaining oxide of lead will be somewhat less than it is 

 given by Klaproth : but the quantity of phosphoric acid can 

 scarcely be oljtained with accuracy by the method which he 

 employed, in precipitating it with lead. Thus calculiited, the 

 composition of the mineral may be stated in the following pro- 

 portions : 



Phosphate of lead 87-66 



Chloride of lead 10-07 



Chromate of lead 01-20 



Water and combustible matter . . 00-40 

 Silex, lime, red oxide of iron . . . 00*67 



100-00 



LXIII. Some Rouarlcs on a Memoir by M. Poisson, read 

 to the Academy of' Sciences at Paris, Nov. 20, 1826, a?id in- 

 serted in the Conn, des Tems 1829. By J. Ivory, Esq. 

 M.A. F.E.S.* — 



Magna vis veritatis. 



TN the Cotm. des Tems 1829, lately published, there is in- 

 -''- serted a long Memoir by M. Poisson, on the attraction of 

 spheroids. The intention of it is, to vindicate the theory of 

 the figure of the planets contained in the Mec. Celeste, from 

 all the objections that have been urged against it. The talents 



* Comnninicatci! by tiic Avillior. 



and 



