On €alcanms aitd Gypjious Earths. 49 



•water in diftillation, but much lefs from fnow than from rairi 

 water. Do8;or Black admits that both nitre and common fait 

 are fornied in the air. A farmer needs no better proof of the 

 exiftence of the latter in the atmofphere on die fouth fide of 

 the Highlands, than the indifference which cattle fliew there for 

 fait, and the eagernefs with which they feek it at a greater 

 diftance from the fea. I fliall now endeavour to reconcile 

 certain phenomena in the operation of Gypfum to this theoiy. 



ift. It benefits dry more than wet foils. 



Because Calcarious and Gypjious earths are at all times 

 foluble in the water. In wet foils they will be diffolved and 

 wafli away ; befides the moifture which invelopes the particles 

 of Gypfum, proteQ it from the adion of the air, and prevent 

 the combinations on which this theory is founded. As lime- 

 ftene is lefs foluble in water than Gypfimiy perhaps if applied 

 in larger quantities, it may be more beneficial to moill land. 



2d. It is proportionally more advantageous to poor than to 

 rich foils. 



ift. Because the putrid vegetables which compofe a rich 

 mold aflFord a fufficient quantity of alkalies, oils and acids, but 

 principally becaufe after the Gypfum has parted with its acid by 

 combining with the alkali, as before fuppofed, its earth being 

 thereby rendered cauftic, combines with the oils with which 

 fuch foils abound, and is thus fhekered from any further opera- 

 tion of the air upon it. Perhaps too the vitriolic acid inflead 



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