MappliKj Soils and Alkali, 29 



strongest alkali soils from different places over the whole area. 

 Fill a large cup, tumbler, or bottle about one-third full with a crust 

 or soil, using more or less, according to the richness of the mate- 

 rial, and nearly fill the receptacle with distilled water. Stir or 

 shake vigorously several times and filter off a pint of the solution, 

 using the filter pump. Rinse out the filter pump after each sam- 

 ple. Treat the eight or ten crusts or soils in the same way. The 

 presence of .black alkali wn 1 1 frequently give the solutions a red- 

 dish color, but this can be ignored. Determine the electrical 

 resistances of the solutions in the cell. Take an amount of the 

 strongest solution equivalent to approximately 200 cc. having a 

 resistance of about 5 ohms, and add to it a volume of each of the 

 others proportional to the resistances determined. If the resist- 

 ance of this mixture, containing approximately equal quantities 

 of salts from the eight or ten localities, is 10 ohms or less, it can be 

 used directly for the standardization. If the resistance is greater 

 than 10 ohms, the solution should be evaporated until the resist- 

 ance is sufficiently low. Carefully measure out 100 cc. of this 

 composite solution and transfer it to a small dish which has been 

 carefully cleaned, dried, and accurately weighed to centigrams. 

 Evaporate to dryness, ignite very gently to free the sulphates and 

 carbonates of water of crystallization, let cool, and again weigh. 

 The gain in weight will give the percentage in salts in the com- 

 posite solution. This percentage divided into any percentage in 

 the following table multiplied by 100 will give the number of 

 cubic centimeters of the composite solution required to be diluted 

 to 100 cc. in order to obtain the corresponding percentage in first 

 column of the table. If the volume thus secured for some of the 

 higher concentrations exceeds 100 cc, it should be reduced to 

 100 cc. by evaporation. Ordinarily a 3J per cent solution is as 

 concentrated as will be required, as this represents 1 per cent of 

 salt in the soil. The electrical resistance of this 3J per cent solu- 

 tion in any cell, divided by 0.24, will equal the resistance of sand 

 or sandy loam in the same cell when completely saturated and at 

 a temperature of 60° F.", when the soil contains 1 per cent of salt. 

 The composite solution is to be diluted and the resistance deter- 

 mined at the various concentrations, corresponding to the limiting 

 values of the alkali map for four grades of soil. 



