T. H. Means — Soluble Mineral Matter in a Soil. 265 



resistance, due to the addition of the solid non-conducting par- 

 ticles, was therefore determined. In this way a large number 

 of samples were examined and it was found that the increase 

 in resistance was nearly the same for soils of very different 

 textures. The following table contains the most important of 

 the results : 



Number of 



letermina- 



tions. 



Soil and character. 



| Loess, Virginia City, III. Silty 



Limestone soil, Blacksburg, Va. Heavy clay 



II u u u u 



Red Land, S. C. Clay soil 



u u u 



j 



Sea Island, Cotton soil, S. C. Fine sand 



Early Truck soil, Md. Coarse sand 



Per cent 

 water when 

 saturated.* 



Initial 



resistance. 



Ohms. 



Resistance 

 after soil 

 is added. 

 Ohms. 



Factor ot 

 texture. 



31-84 



1 



1-81 



•551 



35*36 



1 



1-73 



•579 



69-41 



1 



1-90 



'527 



72-49 



1 



185 



•542 



40 00 



1 



1-83 



•557 



36-35 



1 



1-88 



•533 



3276 



1 



1-93 



•517 



25-77 



1 



1 83 



•547 



17-94 



1 



1-78 



•563 







Average 



•548 



These soils, as seen in the table, vary from the light sandy 

 lands, which require less than 18 per cent (of their dry weight) 

 of water to- saturate them, to the heaviest of clays, requiring 

 TO per cent of water for saturation. Determinations were 

 made with two or three amounts of water in some of the soils 

 in order to strike as near as possible the point of saturation. 

 The last column is the ratio between the resistance after the 

 soil was saturated and the initial resistance of the solution. If 

 the resistance (between parallel electrodes) of a saturated soil is 

 multiplied by this figure (the factor of texture), the resistance 

 of the solution between the soil grains will be found. 



The salt determination is performed in practice as follows : 



1. Saturate the soil with distilled water. The point of satu- 

 ration can very easily be found and, with a little practice, 

 duplicate samples can be mixed to within a small error. 



2. Pack saturated soil in a cubic cell with two sides of metal 

 and take the resistance. Read the temperature, and correct 

 resistance for temperature.f Multiply the corrected resistance 

 by the factor of texture, 0*55. This gives the resistance of the 

 soil solution alone in the cubic cell. 



3. From the known weight of soil in the cell and the per- 

 centage of water required to saturate the soil, find the number 

 of cubic centimeters of soil moisture between the soil grains. 

 In field work it is sufficiently accurate to take the average of 



* Calculated on dry weight of soil. 



f Bulletin 7, Division of Soils, Department of Agriculture. Bulletin 8, Division 

 of Soils, Department of Agriculture, page 27. 



A.M. Jour. Sci.-- Fourth Series, Yol. VII, No. 40. 

 18 



-April, 1899. 



