174 ESSAYS AND OBSERVATIONS 



turbid. But it did not fenfibly efFervefce with 

 acids. 



The mag7iefia, when taken out of the re- 

 tort, weighed an ounce, three drams, and 

 thirty grains, or had loft more than the half 

 of its weight. It ftill effervefced pretty briik- 

 ly with acids, tho' not fo ftrongly as before 

 this operation. 



The fire fhould have been raifed here to 

 the degree requifite for the perfe6^ calcinati- 

 on of mag7iefia. But even from this imper- 

 fect experiment, it is evident, that of the vo- 

 latile parts contained in that powder, a fmall 

 proportion only is water ; the reft cannot, it 

 feems, be retained in veffels, under a vifible 

 form. Chemifts have often 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 

 body, under a folid form, was fet free and 

 rendered fluid and elaftic by the fire. We 

 may therefore fafely conclude, that the vola- 

 tile matter, loft in the calcination of magnefiay 

 15 moftly air j and hence the calcined mag- 



nefa 



