220 ESSAYS AND OBSERVATIONS 



perfedly cauftic ; for it dill yielded fome iiir 

 when mixed with acids, and alfo rendered 

 lime-water turbid : neither of which would 

 probably have happened if I had ufed a 

 greater quantity of magnefia, or had allowed 

 the mixture to remain a longer time in the 

 vial. I now waflied out the whole of the 

 mixture into a bowl, and dryed the magnefia 

 until it loll all fmell of the alkali. It 

 weighed a dram and fifty eight grains, effer- 

 vefced violently with acids, and therefore 

 contained a large quantity of air, which had 

 been drawn from the alkali by a flronger 

 attradion. 



Having formerly fhewn, that magnefia 

 faturated with air feparates an acid from a cal- 

 carious earth, which it is not able to do after 

 being deprived of its air by fire ; I now 

 fufpeded that the air was the caufe of this 

 feparation, becaufe I found that it was joined 

 to the calcarious earth at the fame time that 

 the acid was joined to the earth of magnefia; 

 and imagined that a pure calcarious earth 

 might poffibly have a ftronger attraiflion for 

 acids than a pure earth of mgnefia. 



I therefore diffolved two drams of magne- 

 fia in the marine acid, and thus obtained a 



compound 



