on the Compofition of J a ivies’s Powder. 353 
Kttle of the mixture was made quite red hot for a quarter ot 
an hour further ; during which no fume was feen, or fmell 
perceived. After cooling, a light grey or cineritious heavy 
powder was left ; 011 examining which, argenti wtfpicula were 
feen in the larger grains of this calcined fubftance. It weighed 
2200 grains, therefore the lofs of weight was 45 P er cen ^ 
The Wedgwood pyrometer pieces indicated 8°. In other 
fimilar experiments the lofs, by calcination, was from 37 to 41 
per cent . ; therefore the mean proportion loft in thefe experi- 
ments muft be ftated at 41 per cent . 
It appears, that the calcination of antimony with bone-afties 
is much more fpeedy than when by itfelf, but the degree of 
fire was a little greater in the laft experiment than in that with 
antimony alone. Confidering the nature of thefe experiments, 
perhaps, it may be more reafonable to impute the 3I per cent . 
greater lofs in this laft experiment than the fum of the lofs in 
Exp. i. and 2. to the greater infenfible fubiimation of the calx 
from more fire in one cafe than in the other, than to refer it 
to the larger quantity of air combined with the metal in the 
former of thefe two laft experiments. 
exp. iv. The above light clay or aftv coloured powder, 
obtained in the laft experiment by calcining together anti- 
mony and bone, being expofed to various degrees of fire from 
20 0 to 165° of Wedgwood’s pyrometer, in clofe crucibles, 
was not at all increafed in weight, but generally loft about 5 
per cent . when a pretty large quantity, as a pound, was in the 
veflel. A part of this lofs muft be referred to the adhefion or 
vitrification of the charge with the fides of the crucible, and 
part to the deficiency of the bone itfelf, as above ftiewn, by 
further expofure to fire. I am fenfible, that in experiments of 
this nature all calculation muft neceffarily, to a certain degree, 
Vol. LXXXI. A a a be 
