J. A. Prescott 113 



absorption being thus a manifestation of capillarity. Way pointed out 

 that this physical action deals with the salt as a whole; in the type 

 of soil absorption with which he was working, bases only were affected. 

 This pointed to a chemical action. Again, while physically absorbed 

 substances could be washed out with water, the chemically absorbed 

 substances were completely insoluble. 



In a following paper^ Way develops the idea of absorption by 

 precipitation of insoluble compounds in the soil. He assumed the 

 presence in the soil of a small proportion of double silicates of lime and 

 aluminium which by reaction with salts of ammonia or potassium gave 

 rise to insoluble ammonium or potassium aluminium silicates and the 

 corresponding calcium salts. He prepared double silicates by mixing 

 solutions of alum and sodium silicate — a double silicate of sodium and 

 aluminium was precipitated which by treatment with excess of calcium 

 chloride gave the corresponding calcium compound. 



The behaviour of this calcium compound towards salts was in every 

 respect similar to that of soils and Way had "every certainty" that 

 these double decompositions were " the efficient cause of the singular 

 power." 



These experiments were subsequently confirmed by A. Voelcker^ 

 who attributed the beneficial effect of common salt as a manure to its 

 action in setting free potassium from its combinations in the soiF. 



R. Warington* also held that the phenomenon was to be explained 

 on chemical grounds. He found that precipitates of aluminium and 

 iron hydroxides were also efficient absorbents for both phosphates and 

 bases; this he explained as due to the weak chemical affinity. He 

 supposed that to these oxides was due at least to some extent the 

 peculiar properties of soils, but he did not deny the possibility of the 

 presence of Way's double silicates. 



Liebig^s physical hypothesis. 



J. V. Liebig^ criticised Way's hypothesis. He compared the action 

 of the soil with that of wood or animal charcoal, and regarded the attrac- 

 tion of soil for salts as being of a purely physical nature. He divided 

 plant food constituents into two classes, one chemically and the other 



1 Journ. Boy. Ag. Soc. 1852, 13, 123 



2 Ibid. 1860, 21, 105; 1864, 25, 333. 



3 Ibid. 1865, 26, 298. 



4 Trans. Chem. Soc. 1868, 21, 1. 



5 Ann. Chem. Pharm. 1858, 105, 109; 106, 185. 



Journ. of Agric. Sci. viu 8 



