8 GILLESPIE: HYDROGEN-ION CONCENTRATION IN SOILS 



of acid substance. However this may be, a complete study of 

 soil acidity must take both factors into consideration. 



The lime requirement method of Veitch 1 and its numerous 

 modifications, as well as all other titrimetric methods, for ex- 

 ample, that of Baumann and Gully 2 and that of Daikuhara, 3 

 are an attempt to measure the quantity of acid substance, not 

 the intensity of acidity. Furthermore, since a complete determi- 

 nation of the acids and bases in soils is as yet impossible, one can- 

 not calculate the intensity of acidity from the quantity of acid 

 substance, even if this could be determined by any of the methods 

 yet proposed. The intensity of acidity, or of alkalinity, can 

 only be determined experimentally by a measurement of the 

 hydrogen-ion concentration. 



In a study of the acids and colloids of humus Fischer 4 meas- 

 ured the hydrogen-ion concentrations of some soils by the electro- 

 metric method. He added, when necessary, just enough water 

 to the soil to make possible an intimate wet contact between the 

 soil and the wire electrode. He was able to demonstrate the acid 

 nature of Hochmoor sphagnum (six samples). These showed a 

 hydrogen-ion concentration of 9.6'10~ 4 to 6.5'10~ 4 . Two Flach- 

 moor samples were slightly acid (6'10 -6 and l.l'lO -6 ); another 

 soil and a sample of compost were slightly alkaline (2.7' 10 ~ 8 

 and 4'10 -8 ). Litmus did not respond to the weak acidities or 

 alkalinities of these samples, but did give an acid reaction with 

 the samples of Hochmoor sphagnum. Fischer states that it can 

 be concluded from this that adsorption processes are not to be 

 assumed to vitiate tests of acidity made by means of indicators. 



Fischer had no other test with which to check his electro- 

 metric results, and his electrometric procedure was one that 

 would not be expected to lead to a quick attainment of equi- 

 librium. He was therefore obliged to continue the observations 

 until the potential became constant. Seven to eight hours 

 were required for this, and in the case of the soils which showed 



1 Journ. Am. Chem. Soc, 24: 1120. 1902. 



2 Naturw. Ztschr. Forst- u. Landw., 6:1. 1908. 



3 Bull. Imp. Cent. Agr. Exp. Sta., Japan, 2:1. 1914. 



4 Kuhn-Archiv (Halle), 4: 1-136. 1914. 



