REFERENCES 103 



until it remains constant for some time. This maximum 

 temperature is recorded as the freezing point of the soil. 

 By this method, as by the electric bridge, the quantity 

 of moisture in the soil plays an important part in the 

 concentration of the solution, hence it is essential that 

 a constant quantity of water be present. Fine soils 

 show the influence of changes in moisture content much 

 more than do sands or other coarse soils. In this method, 

 as with the bridge, the determination is indirect and to 

 get the total salts the depression of the freezing point must 

 be referred to the depression of soils under similar con- 

 ditions with known quantities of salts. The limitations 

 of the method have not been worked out as yet, but much 

 is hoped from it. 



Biological Method. -- Another indirect method being 

 developed by biologists is based on the effect of alkali salts 

 on bacterial action. This method has been extensively 

 used by Lipman, Greaves, and Brown and their co-workers 

 and depends on the influence of soluble salts on the am- 

 monifying, nitrifying, and nitrogen-fixing organisms. Sev- 

 eral experimenters have noted that the change in the 

 quantity of salts present in soils affects the soil flora 

 somewhat in proportion, but to what extent this activity 

 may be taken as an indication of the salts present is yet 

 to be seen. 



REFERENCES 



i. Barnes, J. H., and Axi, Barkat. Alkali Soils: Some Biochemical 

 Factors in Their Reclamation. Agr. Jour. India, 12 (191 7), pp. 368- 

 389. (Abs. E. S. R. 38, p. 815.) 



2. Beam, W., and Freak, G. A. An Improvement in the Electrical 



Method of Determining Salt in Soil. Cairo Sci. Jour. 8 (1914), 

 pp. 130-133. (Abs. E. S. R. 32, p. S06.) 



3. Bouyoucos, G. J., and McCool, M. M. The Freezing-point Method 



as a Means of Measuring the Concentration of the Soil Solution 



