348 Dr . Pearson’s Experiments and Obfervalions 
ner. s proportions, viz. two parts of antimony and one of 
calcined bone, and equal weights of bone fhavings and aiiti- 
mony. The quantity of this calx was, however, greater in 
the powder from the former of thefe two laft proportions than 
the latter of them; which latter correfponded fometimes 
exa&ly, and always nearly, with the weight of the calx from 
a given weight of James’s Powder. Thi3 calx afforded alfo 
the fame proportion of Algaroth powder as the calx in James’s 
Powder; and the infoluble part of the calx afforded metallic 
grains like thofe from the infoluble part of the calx in that 
powder. 
I found then an exa£l correipondence between what I confi- 
der to be the efl'ential and peculiar properties of James’s Powder, 
and the properties of a powder made by uniting or mixing 
together the ingredients of James’s Powder found by analyfis.. 
But, in order to fhew the identity or difference of the qualities 
of thefe two fubftances, I made comparative obfervations on 
them, and repeated the above analytic experiments on James’s 
Powder with the preparation made by calcining together equal 
weights of bone fhavings and antimony, in an open veflel, to 
carry off the fulphur, and then in clofe veffels applying fuch a 
degree of fire as to render them white, that is, on the fame pre- 
paration as the Puhis antimonialis of the London Pharmacopeia. 
Firft, I compared, more particularly, the fenfible qualities 
of feveral different fpecimens of James’s Powder with various 
parcels of the Ptilvis antimonialis made by different chemifts. 
All of thefe would be called white powders, but not two of 
them were fo in the fame degree. Moftof the papers of the Pul- 
vis antimonialis were whiter than thofe of James’s Powder ; but 
others were of a very light ftone colour, and fome had a fhade 
of yellow, fo as to refemble very exactly James’s Powder ; 
but 
