350 



NATURE AND PROPERTIES OF SOILS 



concentration, tte importance of alnmimim in acidity cannot 

 be avoided. 



RELATIVE WEIGHTS OF BARLEY AND RYE GROWN IN WATER CUL- 

 TURE. THE HYDROGEN ION CONCENTRATION IS EX- 

 PRESSED IN Ph.^ 



Treatment 



H Ion 



Concentra- 

 tion Ph 



Relative Weights 





Baeley 



Eye 



Check 



6.3 

 4.2 

 4.2 

 3.9 

 3.9 



100 

 93 

 68 

 73 



47 



100 



H.SO^ J 



95 



AL(SO^), 



65 



•^"'■•^•a \ ^^ 4 / 3 « . . • 



H2SO4 



65 



AL(SOJ, 



55 



•*"*"*-2 \'^^4/3 





The only conclnsion possible at the present time is that 

 there are probably several kinds of acidity and many degrees 

 of the same acidity as far as toxic influences are concerned. 

 Moreover, dissimilar plants seem to be affected differently by 

 the same acidity, while the same plants respond diversely at 

 different times. Hoagland ^ and others ^ have demonstrated 

 that some plants grow better in a slightly acid medinm, which 



^The hydrogen ion concentration of an acid in solution is a measure 

 of the dissociation of that acid and of its strength. The specific acidity 

 of pure water is taken as 1, the number of grams of H+ ions to a liter 

 being .0000001 or 10-^. The exponent of the power is taken as an expres- 

 sion of the acidity. Pure water has a Ph value of 7, which is approxi- 

 mate neutrality. An acid solution containing 4000 times more H+ ions 

 would have a Ph value of 3.4. 



^Hoagland, B. E., Belation of the Concmtration and Beaction of 

 the Nutrient Medium to the Growth and Adsorption of the Plant; 

 Jour.^ Agr.^ Ees., Vol. XVIII, No. 2, pp. 73-117, 1919. 



® Gillespie, L. J,, The Beaction of the Boil and Measurements of 

 Eydrogen ion Concentration; Jour. Wash. Acad. Sci., Vol 6, No. 1, 

 pp. 7-16, 1916. 



Sharp, L. T., and Hoagland, D. E., Acidity and Adsorption in Soils 

 as Measured ly the Eydrogen JEleotrode; Jour. Agr. Ees., Vol. VII, 

 No. 3, pp. 123-145, 1916. 



Gillespie, L. J., and Hurst, L. A., Bydrogen-ion Concentration — Soil 

 Type— Common Fotato Seal; Soil Sci., Vol, VL No. 3, pp. 219-236, 

 1918. » > i^i^ > 



