on the Compofition of James’s Powder. 357 
repeated expofure to fire, it never could be made quite fo white, 
but Teemed more inclined to melt than the powder prepared 
■with unburnt bone. In other refpedts the effe&s of fire were 
apparently the fame, or nearly fo, as in the experiments 
with bone fhavings, Exp. 3, 4. ; for though the lofs cf 
weight in this experiment, reckoning that of the antimony at 
29! per cent., and that of the boneafhes at 2! per cent, thould 
have left 2483 only, itiftead of 2550; yet, in other fimilar 
experiments, the product correfponded nearer to this calcula- 
tion, and the lol's was fometimes lefs both of the antimony 
and bone calcined feparately. Some of the perfons who pre- 
pare the Pulvis antimonialh fay, that the whiteft colour is 
obtained by firft boiling the bone fhavings to diffolve their 
mucilage, and then calcining them with antimony as above 
fhewn. Mr. Lile’s receipt dire&s previous decoction of the 
hart’s horn. 
It will not be difficult, from thefe experiments, to give a 
probable reafon for the James’s Powder being generally of a 
yellowifh caff, and for different parcels of it, as well as of the 
Pulvis antimonialis , being generally of different degrees of white- 
nefs and ffiades of yellow. The colour of this preparation is, 
however, a very delicate one. I once directed a perfon to 
calcine together antimony and bone fhavings, in the ufual 
manner, to that ftate in which the white powder may be 
produced by a due degree of fire; but, inflead of a fnow-white 
mafs, I could not by any degree of fire obtain any colour 
but a dirty whitith or light ftone colour,; though repeated 
calcinations were employed. The reafon of the failure 
was, that the earthen difh had been broken during the 
calcination, and a few very fmall pieces of it had fcaled off, 
^nd being mixed with the powder occafioned this difappointment 
with 
