On Plaister of Paris, 109 



to a calcareous earth. This acid is well known to be 

 as unfriendly to vegetation, as calcareous earth is favour- 

 able to it, and, upon the proportion of it contained in 

 gypsum, the value of that article, as a manure, depends. 



When calcareous earth is added to any of the acids, 

 they unite, and compose earthy salts, differently named, 

 according to the acid made use of. If this compound 

 contains a due proportion of the acid and the calca- 

 reous earth, it is said to be neutralized; but if either the 

 acid or the calcareous earth predominate, the compound 

 then possesses acid, or earthy properties. 



We suppose, therefore, that, in cases where calca- 

 reous earth is the prevailing principle in gypsum, its 

 beneficial effects as a manure will be visible, because 

 in that case, a portion of the earth roill not he united 

 with the acid, and will therefore he left at liberty to act 

 upon the soil. 



In cases v/here these two ingredients are equally 

 balanced, the compound posseses very little solubility 

 in water. It is, perhaps, in these cases where it produces 

 little effect ; nor is it possible it can ; because unless the 

 parts of any substance are soluble in water, they generally 

 can produce no effect on vegetation. 



Lastly, where the acid predominates in gypsum, of 

 which, however, we recollect no instances, its mischie- 



Since this publication, the gypsum is used in England to 



profitable account. Its properties are better understood and 



I beheve, the use of it is much encouraged. How whimsical 



and inapplicable is this theory ! when we compare it with 



facts generally known here. 



R, P. 

 September, 1810. 



