PHYSICAL AND LITERARY. 37 



of fire, their calcarious earth would ne- 

 cefTarily be deprived of its natural propor- 

 tion of air and moifture ; on which ac- 

 count, the folution of this earth in the 

 muriatic acid, and its fubfequent preci- 

 pitation, by reftoring what was loft in the 

 fire, could not fail confiderably to increafe 

 its weight. And from thence it happens, 

 that the weight of the precipitated pow- 

 ders, added to that of their refpeclive 

 refidues, equalled pretty exadly the 

 weight of the marles before calcination. 



It may bealfo remarked, that the burnt 

 marie of Experiment 22. yielded a fmal- 

 ler proportion of refidue than the fame 

 marie in its natural flate did. For, when 

 this marie was examined as taken from 

 the pit, its unfoluble parts were nearly 

 a third of the whole ; after undergoing 

 the adion of fire, they did not exceed a 

 fifth *. This difference, I imagine, is the 



efFecSl 



* They did not amount to a feventh part of the 

 weight which the marie had before it was put into the 

 file. For the weight of the marie then was 30 grains, 

 the weight of the refidue extraded after calcination was 

 only four. 



