THE MINERAL CONSTITUENTS OF THE SOIL SOLUTION 37 



shaken with distilled water which has been previously boiled 

 to eliminate the dissolved carbon dioxide, the resulting solution 

 will give an alkaline reaction with such indicators as phenol- 

 phthalein or litmus. 1 If a soil be shaken up thoroughly with 

 water, the resulting solution filtered free of suspended matter, 

 as by passing through a Pasteur-Chamberland bougie, and then 

 boiled to eliminate the carbon dioxide, in the vast majority of 

 cases the solution will also give an alkaline reaction with phenol- 

 phthalein or litmus. The waters of most of our springs, ponds, 

 creeks or rivers being natural soil solutions, give an alkaline 

 reaction after boiling. 



But the mineral content of these natural waters varies greatly. 

 These waters are composed in part of the "run-off," in part of 

 a portion of the "cut-off" waters, described above. This por- 

 tion of the cut-off, normally, in passing through the soil goes 

 mainly through the larger interstices. It is not long in contact 

 with the individual soil particles and floccules, and because 

 diffusion of dissolved mineral substances is quite slow, especially 

 in dilute solutions, it takes up but little mineral matter from 

 such aqueous films as it may intercept. 



A different state of things exists with that portion of the cut- 

 off water which returns towards the surface by reason of capil- 

 lary forces, to form the great natural nutrient medium for plants. 

 This water is moving over the soil particles in films, and with 

 slowness. It is long in contact with successive fragments of 

 any particular mineral and all the different minerals making 

 up the soil. Consequently, it tends towards a saturated solution 

 with respect to the mineral mass; and it follows that if every 

 soil contains all the common rock-forming minerals, every soil 

 should give the same saturated solution, barring the presence of 



1 In making such experiments in the laboratory or in lecture demon- 

 strations, it is well to have the mass of water large in comparison with 

 the mass of powdered mineral or rock; otherwise secondary adsorption 

 effects may occur and obscure the results of the hydrolysis. 



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