On Plaister of Paris, 105 



and perhaps a better explanation, is, that in clay soils there 

 is little or no -calcareous earthy on which the plaister always 

 operates the most favourably ; as it finds, in these earths, the 

 carbonic acid in the greatest plenty. 



Dr. Priestly, m a conversation I lately had with him, told 

 me, he was preparing to analyze the gyps I with a, view to 

 farther discoveries of its nature and properties, both chemi- 

 cal and agricultural. I wait, with much curiosity, to know 

 the result of the experiments, or this able chemist and vene- 

 rable philosopher. I am aware, that the doctor's opinions, 

 and those of the followers of Lavoisiere, in several points, 

 differ very materially. I am neither qualified, nor inclined, 

 to determine which are right ; though I have ventured to 

 make deductions, perhaps too hastily, from some of the new 

 chemical theories. The Doctor asserts, that "some plants 

 are chiefly nourished by hydro gene or hijlammahle ai'r^ such 

 as the willow, &c." We see aquatic plants coarse, strong, and 

 capable of being sustained (if so they are) by air which is 

 found the most plentifully in wet grounds, where no tender 

 plants, the occupants of dry soils, will grow. The air, nutritive 

 to the one, may be poison to the other. Clover will not 

 grow well in wet grounds, nor will plaister operate there ; 

 so that clover and plaister seem to be made for each other. 

 The Doctor thinks, that the mjlammahle principle is the 

 prevalent part of the nourishment of plants ; and that they 

 thrive the best in vitiated or phlogisticated air. It will be 

 seen how much other eminent men differ with him, by 

 what has been said by Ingenhausz, &c. The Doctor's 

 opinion of the carbonic acid htm^ injurious to plants, is not 

 in unison with that of Ingenhausz, Kirwan, and others. In 

 Chaptal, page lir,vol. l,it is said, "The carbonic acid is 

 improper for vegetation ; Dr. Priestly, having kept the roots 

 of several plants in water impregnated with the carbonic 

 acid, observed that they all perished ; and in those instances 

 where plants are observed to vegetate in water, or in air which 



o 



