362 Dr . Pearson’s Experiments and Obfervatlons 
certain degree ; 'which is effected by expofure to air and fire with 
the bone-afhes when it can part or combine with air, fo as to be 
reduced to that (late in which it will be duly calcined for union 
with that fubftance, which could not happen in clofe veflels. 
If it be objected, that this explanation does not account for 
the whitenefs of this preparation, which is only produced by a 
white heat, and to which air is not neceflary, the difficulty 
will be removed by confidering that this whitenefs may be in- 
duced without any chemical alteration effe&ed by the fire : for, 
after the fir ft calcination in the open veflel, it feems to adt, prin- 
cipally, in the fame way that it does in making grey coloured 
bone-afhes, or imperfedlly burnt bone, of a lnowy whitenefs, 
namely, by totally deftroying matter extraneous to the phofpho- 
ric felenite. Fire alfo, in many inftances, alters the colour of 
bodies without occafioning any change in their compofition ; 
and, perhaps, the change of the light clay or cineritious pow- 
der, formed by the calcination of antimony and bone-afhes in 
open veflels, to a fnowy- white fubftance by further expofure to 
fire, depends in part upon its increafe of fpecific gravity or 
other mechanical effefts of fire. A ftriking example of the 
power of fire to change the colour of bodies, by merely in- 
creafing their fpecific gravity, is afforded by the operation of 
quartation, in which procels, the filver being parted, the gold 
is left of the colour of copper; but, by expofure to a due 
degree of fire, it is changed to its well known yellow colour, 
without undergoing any alteration except an increafe of fpe- 
cific gravity. 
To /elucidate the nature of the infoluble and infufible part of 
James’s Powder, I made the following experiments, in which 
I particularly had in view to determine whether feveral anti- 
monial calces be wholly foluble in acids. 
EXP, 
