On Calcarious and Gypjious Earths. 39 



Vith alkalies, of forming a fait which fhall diffolve in water, 

 and fit all thefe fubilances for entering the abforbent veifcls 

 of plants. 



[Watfon's El: 257.] Vegetables, on diflillation, yield 

 earth an acid liquor, fixed and inflammable air, an oil and an 

 alkali. In fome vegetables the acid and alkali are a£lually 

 fouad united, as in tobacco, fun-flowers, &c. and although 

 chymifts doubt whether the alkali is not produced from the 

 acid in the a8; of combuftion, yet I think this queftion is 

 decided by the analyfis of tartar, which the vinous juice of 

 moft plants yield, and which is found to confift of an acid and 

 an alkali. MacgrafF obtained pure nitre from it by faturating 

 it with nitrous acid. 



From this analyfis of limeftone, v;hich only differs from 

 Gypjum in the acid with which it is combined, we might be 

 led to conclude that it aided vegetation, by being converted 

 into the food of plants. But how is it poflTible to conceive 

 that fix bufhels of this manure, which does not weigh five 

 hundred pounds, fliould be converted into twenty thoufand 

 weight of grafs, which it will produce in two years on the 

 poorefl foil? Why will it not have the fame effett in the 

 vicinity of the fea, or on wet grounds ? And wlience do the 

 plants derive their oil and alkalies, fince neither are found in 

 this manure ? 



