222: ESSAYS AND OBSERVATION'S 



air, is greater than the fum of the forces 

 which tend to join the calcarious earth to 

 the acid, and the magnelia to the air : and 

 becaufe there is a repulfion between the acid 

 and air,, and between the two earths ; or they' 

 are fomehow kept aftinder in fuch a manner 

 as hinders any three of them from being 

 united together ? 



The firft part of this fuppolition is favour- 

 ed by our experiments, which feem to (hew 

 a greater difference between the forces 

 wherewith the calcarious earth and magnefia 

 attradt fixed| air, than between thofe which 

 difpofe them to unite with the acid. The 

 repulfions however hinted in the fecond are 

 perhaps more doubtful, tho' they are fug- 

 gefted in many other inftances of decom- 

 .pofition ; but the bounds of my prefent pur- 

 pofe will not allow me to enter upon this 

 fubjefl, which is one of the moft extenfive 

 in chemiilry. 



We meet alfo with a difficulty with re- 

 fpedl to the volatile alkali limilar to the 

 above. Thus a calcarious earth that is pure 

 or free of air has a much ftronger attraction 

 for acids than a pure volatile alkali, as is evi- 

 dent when we mix quick-lime with fait 



ammoniac ; 



