PHYSICAL AND LITERARY. 47 



fition, difcovered the fame proportions 

 of calcarious earth and clay, as when it 

 was taken from the pit. 



Mar l e, when ufed as a manure, being 

 generally fuppofed to atradl from the 

 air a certain acid fpirit, with which it 

 combines into a neutral fait, the power- 

 ful promoter of vegetation ; I fliall here 

 add an account of two Experiments, 

 made with a view to afcertain the exi- 

 ftence of that fait. 



EX PER. XXX. 



Two drachms of clay-marle, which had 

 been expofed to the air for fix months, 

 were digefted, with a confiderable heat, 

 in ten ounces of water. This water, after 

 24 hours, was filtered off, and the^ fame 

 quantity again added. After the fame 

 fpace, this fecond water was alfo filtered 

 off. The marie being then dried, want- 

 ed a grain of its original weight. None 

 of the filtered waters fuffered any change 

 from the addition of an alkaline fait. 

 Both of them were, by a gradual evapo- 



ration^ • 



