10 GILLESPIE. - HYDROGEN-ION CONCENTRATION IN SOILS 



saturated potassium chloride solution and the soil extract. By means 

 of a motor the vessel could be swung about an axis at x; during the mo- 

 tion the body of the electrode vessel turned from an inclination of 3° 

 to the horizontal to an inclination of about 33° to the horizontal. The 

 electrode vessel had a capacity of about 65 cc, measured from the brim 

 to the stopcock. 



Fifteen grams of dry soil were introduced into a test-tube 17 by 3 

 cm., 30 cc. of distilled water were added, and the mixture was well 

 shaken and permitted to stand about 10 to 20 minutes for sedimentation. 



Fig. 1. The filled electrode vessel. 



The neck of the electrode vessel, including the bore of the stopcock, 

 was filled with a portion of the soil extract so obtained and the stopcock 

 was then closed. The end-tube a was filled with saturated potassium 

 chloride solution by means of a capillary pipette. The rest of the soil 

 mass was now well agitated and immediately poured into the vessel, 

 which was then fastened to the shaking device. A rubber tube, filled 

 with the saturated potassium chloride solution which led to the calomel 

 electrode through a closed, ungreased stopcock, was joined to the tube a, 

 and the vessel was closed with a well-fitting rubber stopper carrying the 

 electrode and tubes for the entrance and exit of hydrogen. A volume 

 of about 140 cc. of dry hydrogen, electrolytically generated from caustic 

 potash solution A with iron electrodes, was rapidly swept through the 



