264 T. H. Means — Soluble Mineral Matter in a Soil. 



Art. XXYI. — A Rapid Method for the Determination of the 

 Amount of Soluble Mineral Matter in a Soil; by Thos. H. 



Means. 



A rapid and simple method for the determination of the 

 per cent of soluble matter which a soil contains has been found 

 very desirable where areas of soil are to be studied in any 

 detail. Particularly is this true in the arid and semi-arid 

 regions of the West where accumulations of soluble salts have 

 been the cause of injury to valuable tracts of land. The ordi- 

 nary methods of chemical analysis are entirely too laborious 

 for the examination of a large number. of samples, and, besides, 

 chemical analyses cannot be made out in the field. In field 

 studies it is of great advantage to know the salt-content of the 

 soil at hand. The accumulation of " alkali," wherever irrigation 

 has been practiced a few years, has pointed out the great neces- 

 sity of studying the conditions of the soluble matter before 

 water is applied. Enormous sums of money are being invested 

 in irrigation, and a great deal of this expended capital has 

 been, or will be, lost unless new systems of irrigation and 

 drainage are devised. There can be no question that the study 

 of the soil, the alkali and the methods for the prevention of 

 its accumulation, must form an integral part of every irrigation 

 engineering problem. .Not only must the surface of the soil 

 be examined, but the per cent of salt found in the subsoil to a 

 depth of 30 or 40 feet should be known. In order that under- 

 ground maps of the salt may be prepared with much greater 

 ease than is possible with ordinary means, the following 

 method is suggested. 



The electrical conductivity of water varies with the amount 

 of dissociated salt that is present. The method is practically a 

 means of determining the specific electrical conductivity (or 

 resistance) of the solution between the soil grains. When this 

 is known, the amount of any salt which will produce this same 

 conductivity may be calculated from published tables of the 

 conductivity of salt solutions.* 



In order to determine the effect of the solid grains of the 

 soil upon the resistance of the solution, the following experi- 

 ment was arranged. A hard rubber cell with parallel sides of 

 metal was partly filled with a solution of known specific 

 resistance. Then as much dry soil was added as would be 

 taken up by the solution, forming a saturated soil. The 

 resistance was in all cases increased. A correction was made 

 for the soluble matter contained in the soil, and the increase in 



* Kohlrausch, Wied. Ann., 18*79, vol. vi, p. 145. 



