592 STATE BOARD OF AGRICULTURE. 



THE FREEZING POINT METHOD AS A NEW MEANS OF MEASUR- 

 ING THE OONCENTRATION OF THE SOIL SOLU- 

 TION DIRECTLY IN THE SOIL. 



Technical Bulletin No. 24. 



BY GEORGE J. BOUYOUCOS AND M. M. McCOOL. 



INTRODUCTION. 



A definite knowledge of the concentration of the soil solution as it 

 actually exists in the soil, under all conditions, including variation in 

 moisture content, tillage, fertilizer treatment, season, etc., is of the 

 greatest importance and highest interest from all standpoints — the 

 chemical, physical, physiological, and biological. At present, the exact 

 concentration of the natural soil solution under all the conditions 

 enumerated above is not known, as there has been no method capable of 

 executing a direct measurement of its magnitude. 



In the present bulletin there is presented the freezing point method 

 as a new method capable of measuring the concentration of the soil 

 solution directly in the soil under a variety of conditions, and some of 

 the experimental data obtained. 



I 



REVIEW OF PREVIOUS METHODS. , 



I 



A large number of methods have been used to ascertain the concen-^ 

 tration of the natural soil solution, but nearly all of them are based 

 upon the general principle of extracting or isolating the solution from 

 the soil and measuring its concentration, besides other properties. The 

 one method most extensively employed is that developed by Whitney 

 and. Cameron, (1), and consists of mixing 100 parts of soil with 500 

 parts of water, stirring the mixture vigorously for 3 minutes, allowing 

 it to stand 20 minutes, and filtering the supernatant liquid through 

 Chamberland-Pasteur filters under pressure. The results obtained by this 

 method led Whitney and Cameron to advance the theory that the soluble 

 mineral matter of the soils produces in general a saturated or nearly 

 saturated solution in the soil moisture; that the magnitude of concen- 

 tration of this soil solution is the same for practically all soils; and, 

 that it is generally low, but sufficiently high for the growth and develop- 

 ment of crops. 



By employing the same method, other investigators have obtained 

 different results and have arrived at different conclusions from those 

 of Whitney and Cameron. One of the most extensive investigations 

 upon the subject is that of King. (2). The results he obtained show 

 that the amount of water-soluble material recovered in the water ex- 

 tract is large, and differs very widely in the various soils, and that the 



(•) Bui. 22, Bureau of Soils, U. S. Dept. of Agr., 1903. 

 (») Bui. 26, Bureau of Soils, U. S. Dept. of Agr., 1905. 



