102 METHODS OF DETERMINING ALKALI 



In using the bridge, Beam and Freak (2) found it pos- 

 sible to eliminate calcium sulphate from the total salts 

 by using 40 per cent alcohol in extracting the salt and 

 comparing the resistance with that found for this solvent 

 under known conditions. By determining both alcohol 

 and water extraction results, the difference shows the 

 calcium sulphate. 



Fig. 14. Determining Soluble Salts with the Electric 

 Bridge in the Field. 



Freezing-point Method. - - A method for determining 

 the total soluble salts in soils by means of differences in 

 the lowering of the freezing point due to differences in 

 concentration of the soil solution, has been worked out by 

 Bouyoucos and McCool (3). About an inch of the soil is 

 placed in an isolated tube surrounded by salt-ice water 

 with a temperature of about 4.5 C. and a delicate 

 Beckmen thermometer inserted in the soil. The soil is 

 first supercooled to about 1 degree C. below its freezing 

 point and is then disturbed so that the temperature rises 



