Feb. II, 1918 Effect of Season and Crop Growth on Soil Extract 315 



dissolved by the water extract over and above that portion which was 

 actually in solution. This was a very valuable differentiation. His 

 conclusion that these graphs could be directly produced and would fol- 

 low the concentration of the actual soil solution is discussed by Hoag- 

 land (27) in connection with experimental data bearing on this point. 



Mitscherlich was able by his procedure to distinguish between fertil- 

 ized and unfertilized soils and also between various grades of fertilizer 

 application. An excellent feature of his work was the complete and 

 careful estimation of the factor of error involved for all determinations 

 and its influence on the final result. 



Ishcherekov (29) published the first of numerous attempts, which are 

 still continuing, to obtain the soil solution by the use of various reagents. 

 Briggs (6) and Briggs and McCall (7) had previously obtained small 

 amounts of solution from the soil by centrifugal force and capillarity 

 when the soil contained moisture slightly in excess of the optimum, 

 Ishcherekov now attempted to obtain the solution from a soil which was 

 close to saturation by pouring a layer of 0.5 cm. of ethyl or methyl 

 alcohol over the soil and assumed that the first portion of clear solution 

 which ran through was the actual soil solutio^i. 



The same author later (50) reported a series of studies in which he 

 used the methods of the U. S. Bureau of Soils and from which he drew 

 conclusions which were practically in entire agreement with those of 

 Whitney and Cameron {61). 



Engels {15), on the other hand, reported a series of studies in which 

 he used distilled water, carbon-dioxid-saturated distilled water, and 2 

 per cent citric acid and concluded that the citric acid was the most 

 satisfactory reagent to estimate the soluble material in soil. 



Maschhaupt and Sinnige {41) conducted an investigation in which 

 carbon-dioxid-saturated water and 2 per cent citric acid were employed 

 and concluded that carbon-dioxid-saturated water was preferable. 



Lyon and Bizzell (40) have attempted to estimate the density of the 

 soil solution indirectly by determining the relation of the dry matter 

 formed to the transpiration observed. They conclude that the addition 

 of f ertiUzer caused an increase in the density of the solution and obtained 

 confirmatory evidence by measuring the density of the soil solution with 

 the Wheatstone bridge. 



Van Suchtelen {17, 59) has announced a modification of Ishcherekov's 

 (29) procedure in which he uses paraffin oil instead of alcohol. He 

 claims to obtain the soil solution in unaltered form, though the full 

 details of his method have not yet appeared. As the first announcement 

 of this method appeared in 1912, and the last statement of its pros- 

 pective full publication was made by Morgan {43) in 191 6, it is to be 

 hoped that it may soon appear in its entirety. 



