iPHYSIC AL ANO LITEkARY, 185 



this air certainly adheres to them with confi- 

 derable force, fince a ftrong fire is neceffary 

 to feparate it from magnefia, and the ftrongeft 

 is not fufficient to expell it entirely from fixed 

 alkalis, or take away their power of effervef- 

 cing with acid falts. 



■ These confiderations led me to conclude, 

 that the relations between fixed air and al- 

 kaline fubftances was fomewhat fimilar to the 

 relation between thefe and acids j that as the 

 calcarious earths and alkalis attra£t acids 

 ftrongly and can be faturated with them, 

 fo they alfo attradt fixed air, and are in their 

 ordinary ftate faturated with it : and when we 

 mix an acid with an alkali or with an abfor- 

 bent earth, that the air is then fet at liberty, 

 and breaks out with violence; becaufe the al- 

 kaline body attrads it more weakly than it does 

 the acid, and becaufe the acid and air cannot 

 both be joined to the fame body at the fame 



time. ^ 



I alfo imagined, that, when the calcarious 

 earths are expofed to the aftion of a violent 

 fire, and are thereby converted into quick- 

 lime, they fuffer no other change in their 

 compofition than the lofs of a fmall quantity 

 ^ of water and of their fixed air. The re- 

 .. Vol. IL A a markable 



