THE MINERAL CONSTITUENTS OF THE SOU, SOLUTION 57 



media, as in the space between two concentric cylinders of un- 

 glazed porcelain, the space being closed by a rubber stopper. 

 To the interior cylinder is fitted a stopper carrying a tube of 

 insoluble metal, such as platinum or tin. This tube is bent into 

 a goose-neck form, and just below the stopper the tube is per- 

 forated with a small opening. The whole apparatus is filled 

 with water and set in a beaker, also filled with water. The metal 

 tube is made the cathode in an electric circuit, a platinum or 

 other suitable anode being introduced into the beaker. In a few 

 minutes the dissolved and hydrolyzed bases pass into the cathode 

 chamber, and as the water also accumulates in the chamber by 

 electrolytic endosmosis, a solution of the bases dissolved from 

 the soil minerals drops from the end of the metal goose-neck. 

 By adding water to the outer beaker from time to time, a steady 

 stream of alkaline solution has been obtained for months, and 

 in no case yet has a soil thus treated failed to continue to yield 

 up the bases it contains in its mineral particles. The acids, such 

 as phosphoric acid for example, are of course found in the 

 water outside the porous cells, and in the case of the phosphoric 

 acid it also appears to continue indefinitely to be withdrawn from 

 the soil. 1 It thus appears that as the products of solution and 

 hydrolysis are removed, by such an endosmotic device as that 

 just described or by the roots of growing plants, by leaching or 

 otherwise, the soil minerals will continue to dissolve. 



The foregoing arguments as to the concentration of the soil 

 solution with respect to those constituents derived from the soil 

 minerals, are based on the generally recognized principle that a 

 material system left to itself tends towards a condition of stable 

 equilibrium or final rest, that is, a condition where such changes 

 as are taking place are so balanced that no change occurs in 

 the system as a whole. But the soil is a system continually 

 subject to outside forces and influences, and as pointed out 

 above, is of necessity a dynamic system. It is doubtful in the 

 extreme if any soil in place is ever in a state of final stable 

 equilibrium. It would be natural, therefore, to expect and to 



1 For detailed description of the apparatus and experimental data, see 

 Bull. No.- 30, p. 27, et seq., Bureau of Soils, U. S. Dept. Agriculture. 



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