THE PHYSICO-CHEMICAL INVESTIGATION OF SOILS. 



to exist in their root sap. The first alternative aims to ascer- 

 tain the permanent productive values of soils; the latter to test 

 their immediate productive capacity. Both alternatives are 

 purely empirical, and derive their only claim to practical value 

 from their accordance with practical experience (see chap- 

 ter 19). 



THE SOLVENT ACTION OF WATER UPON SOILS. 



The almost universal solvent power of pure water has 

 already been alluded to in chapter 2 (see p. 18), and illustrated 

 by the analyses of drain and river waters. While these con- 

 vey a general idea of the chief substances dissolved and car- 

 ried off, the direct investigation of the solutions actually ob- 

 tainable from the soil by longer treatment and with no more 

 water than is compatible with the welfare of ordinary crops, 

 necessarily gives somewhat different results. For when 

 drains flow during or after heavy rains the water has not time 

 to become saturated. The following data afford a clearer in- 

 sight into the actual and possible solvent effects of water in 

 the soil, and its possible adequacy to plant nutrition unaided 

 by acid solvents. 



Extraction of Soils with Pure Water. Eichhorn and Wun- 

 der treated soils from Bonn, and from Chemnitz (Saxony) re- 

 spectively for ten days and four weeks with about one-third of 

 their weight of water; the solutions thus obtained contain in 

 1,000,000 parts: 



