i8o 



THE CHEMICAL ANALYSIS OF SOILS [chap. 



of the Rothamsted soils, the soil in its undried state 

 fleing worked up with water in the proportions of 

 20 soil and 35 water. The solutions obtained showed 

 the following compositions, the amounts extracted 

 by dilute and strong acid being appended for 

 comparison. 



Whatever the theories which have been formed as 

 to the manner in which the mineral constituents of the 

 soil pass into solution for the plant, it is improbable that 

 the conditions can be reproduced in the laboratory, and 

 for the practical purposes of analysis the desideratum is 

 a solvent that will dissolve the class of material which 

 is found by experience to reach the immediate crop, but 

 which will not touch the same material should its state 

 of combination or physical condition be such as to render 

 it unavailable for the plant. Various solvents have been 

 proposed: for example, Deherain showed that dilute 

 acetic acid, while dissolving some phosphoric acid from 





