146 



Journal of Agricultural Research 



Vol. XII, No. 3 



EFFECT OF POTASSIUM CHLORID ON THE H-ION CONCENTRATION 



OF SOILS 



As previously shown, neutral salts added to suspensions of certain 

 soils considerably increased their H-ion concentration. This fact has 

 brought up the question as to the effect of the diffusion of potassium 

 chlorid from the agar connecting tube into the soil suspension. In 

 order to determine the magnitude of the possible changes induced in the 

 reaction of soil suspensions by the escape of potassium chlorid into them, 

 several experiments were undertaken. For this purpose it was necessary 

 to eliminate as far as possible the diffusion of potassium chlorid into the 

 soil suspension. As shown in Table II, one procedure consisted in 

 bringing the soil suspension into equilibrium with hydrogen without 

 any possible chance for contamination with potassium chlorid, then the 

 electromotive force was read just as the agar tube touched the suspension, 

 thus reducing the diffusion of the potassium chlorid to a minimum. 

 This reading was then compared with subsequent readings made in the 

 manner heretofore described. In addition, some agar tubes prepared 

 with soil extracts were substituted for the potassium chlorid tubes. 

 The sensitivity of our galvanometer did not allow of a greater accuracy 

 than 0.02 volt when the soil-extract tubes were used. 



It is evident from the data in Table II that the slight diffusion of 

 potassium chlorid from the agar tube has a tendency to increase the 

 H-ion concentration of the soil suspension. In almost all cases this 

 increase corresponds to less than 0.005 volt. For most agricultural 

 purposes this difference has no significance. By bringing the entire 

 system into equilibrium with hydrogen before immersing the agar tube 

 and by keeping the tube out of the suspension except momentarily 

 at the time of reading the electromotive force, it is believed that the 

 error will be entirely negligible. 



