ae 
PHYSICAL anp LITERARY. rot 
half of its weight. It ftill effervefced pret- 
ty brifkly with acids, though not fo —s, 
ly as before this operation, 
THE fire fhould have been raifed here 
to the degree requifite for the perfect cals 
cination of magnefia. But, even from this 
imperfect experiment, it is evident, that, of 
the volatile parts contained in that pow- 
der, a {mall proportion only is water; the 
reft cannot, it feems, be retained in vellels, 
under a vifible form. Chemifts have of- 
ten obferved, in their diftillations, that part 
of a body has vanifhed from their fenfes, 
notwithftanding the utmoft care to retain 
it; and they have always found, upon 
further inquiry, that fubtile part to be air, 
which having been imprifoned in the bo- 
dy, under a folid form, was fet free and 
rendered fluid and elaftic by the fire. We 
may therefore fafely conclude, that the vo- 
latile matter, loft in the calcination of 
magnefia, is moftly air; and hence the 
_ calcined magnefia does not emit air, or 
" make an effervefcence, when mixed with 
| acids. 
THE 
