512 STATE BOARD OF AGRICULTURE. 



The greater the amount of moisture present up to its total water ca- 

 pacity, the more solution can be obtained. It is assumed that every- 

 iliing else being equal, all the solution above a certain i)oint can be ob- 

 tained. Briggs and McLane^ in their work with the centrifuge called 

 tliis point the moisture equivalent, being that amount of moisture re- 

 tained l\y the soil, when the moisture content is reduced by means of a 

 constant centrifugal force until it is brought into a state of capillary 

 equilibrum with the applied force. The same term may be applied here 

 with the understanding that it may vary due to the application of a 

 different force. If we consider the work of these men- we note the force 

 with which the water film is held to the soil particles. In the whirling 

 of moist soils, they find that this film was not removed by a force of 

 3,000 times the force of gravitation. In the paraffin oil pressure method, 

 tlie highest pressure used was only 550 to 600 pounds or about 40 at- 

 mospheres. The thicker the film around the soil particles the less force 

 is required to remove the moisture from the outer edge of the film. Lord 

 Eayleigh^ as a result of some experiments calculated that the thin film 

 was held with a force as high as 25,000 atmospheres. With part of the 

 moisture held by that great force, it would be impossible to get it all 

 with 40 atmospheres. On account of the oil penetrating at least part of 

 the soil, sides, top and bottom, and all of some soils, the amount of 

 moisture that remains is obtained by the difference between the moisture 

 content of the soil and that obtained by extraction. 



In Table III the extractions are classed according to the kind of soil 

 used. The letters S and L refer to the small and large cylinders re- 

 spectively. The percentage of moisture in the soil (M. in S.) is based 

 on oven dried soil. The weight of soil (Wt. of S) used in the extraction 

 includes over dried soil plus the moisture in the soil; that is, it is the 

 weight of the moist soil. The percentage of moisture extracted is based 

 upon oven dried soil, while the percentage of the moisture in the soil 

 (M. in S.) extracted is based upon the total moisture content of the soil. 

 The moisture equivalent (M. E.) obtained is the difference between the 

 percentage of moisture in the soil and that extracted, while the moisture 

 equivalent calculated is determined from their formula* based upon the 

 mechanical analysis of the soil. 



^Briggs, L. J. and McLane, J. W. The Moisture Equivalents of Soils. Bui. No. 45, Bur. 

 of Soils, U. S. Dept. of Agr. pp. 5. and 22. 



-Briggs, L. J. and McLane, J. W. Ibid. pp. 14 and 23. 



^Lord Rayleigb, On the theory of surface forces. Phil. Mag. S. 5, V. 30, pp. 285-298, 456- 

 475, (1890). 



^Briggs, L. J. and McLane, J. W. Ibid. p. 17. 



