32 On the Analysis of Soils. 



Gypsum is to be detected by boiling the earth with 

 alkaline salts; in which case, the gypsum will be decom- 

 posed, and the vitriolic acid of the gypsum will join 

 with the mineral alkali, forming Glauber salt, which is 

 very soluble. The quantity of gypsum previously ex- 

 isting in the soil is to be ascertained by weighing, when 

 properly dried, the calcareous matter which had been 

 precipitated by the alkali ; and by adding thereto, in 

 calculation, the proportion of vitriolic acid necessary to 

 constitute it gypsum ; having previously deducted there- 

 from the proportion of fixable air which the precipitated 

 chalk contains. The proportion of fixable air and vi- 

 triolic acid contained in chalk and in gypsum are in the 

 proportions as here stated: 



Fixable Air Calcareous Matter 



In chalk, 43 53 



Vitriolic yield Calcareous Matter 



In gypsum, 48 34 



The following is given as an example of the method 

 of making this calculation : 



Grai?2s. 

 Residuum of precipitated chalk, - * 480 



Proportion contained therein of fixable air,^ 212 



Calcareous matter, - - . . 268 



Proportion of vitriolic acid necessary to consti- 

 tute gypsum with the calcai'eous matter, 554 



Total quantity of gypsum, - - - 622 



