EXPERIMENT STATION BULLETINS. 593 



soils which produced the largest yields of crops or received application 

 of fertilizers gave the largest amount of soluble material in the aqueous 

 extracts. 



More recently, Hall, (3), et al., obtained results with the Kothamsted 

 soils which agree in general with those of King. These investigators 

 prepared artificial water extracts from certain Kothamsted experiment 

 plots on which wheat and barley had been grown for 60 years and had 

 received different manure treatment, by mixing 20 kgms. of dry soil 

 with 30 kgms. of water. The results they obtained show that the concen- 

 tration and composition of the soil solution are not constant but vary 

 significantly in accordance with the composition of the soil, and its 

 past manurial history. 



This method, therefore, has apparently not only failed to give con- 

 cordant results as to the concentration of the extract in the different 

 soils, but also it tells nothing as to the exact concentration of the true 

 solution of the soil. The addition of the water to the soil not only 

 dilutes the natural soil solution, but also may cause a dissolving action 

 upon the minerals, a suspension of the hydrosols, a dialysis of sub- 

 stances absorbed by hydrogels, etc. 



Various investigators have attempted to obtain information regard- 

 ing the concentration and composition of the soil solution by collecting 

 and analyzing the drainage water of the soil. This method, however, 

 is not only open to all the above objections, but also to the additional 

 one that the drainage water may percolate through the spaces between 

 the particles and may not come in comj>lete intimate contact with the 

 film of water around and in the soil particles, and since the processes 

 of diffusion are slow, the drainage water may not be a true representa- 

 tive of the natural solution existing in the soil. 



On account of the above objections to using water in isolating the 

 natural soil solution, some investigators have tried to extract it di- 

 rectly from the soil by mechanical means. Two different methods have 

 been employed to accomplish this purpose, namely, the centrifuge, and 

 the paraffin oil. The centrifuge method has been developed and employed 

 by Briggs, (4), and consists of whirling whetted soils in a rapidly re- 

 volving centrifuge fitted with concentric cylinders, the middle one hav- 

 ing fine perforations, and developing a force equivalent, on the average, 

 to 3,000 times the attraction of gravity. The soil solution is thrown 

 out through the perforations and collects in the spaces between the per- 

 forated middle cylinder and outer cylinder. It collects usually as a 

 perfectly clear solution, requiring no filtration. The results yielded by this 

 method, however, have not been entirely satisfactory, owing: (1), to the 

 small quantity of the soil solution obtainable at a time for analysis; 

 (2), the liquid obtained is the excess or free water thrown out from the 

 saturated soil and may not possess exactly the same concentration and 

 composition as the film water remaining. That the concentration of 

 the solution obtained might not be and probably could not be absolutely 

 the same as the entire moisture of the soil, seems to be suggested by 

 the following considerations : If the solution is not saturated or in 

 equilibrium with the soil components, then the films which are in in- 



(») Jour. Agr. Scl. 6, 1914. 



(*) Buls. 22 and 31, Bureau of Soils, U. S. Dept. of Agr., 1905 and 1906 respectively. 



75 



