THE FORMS OF SOIL WATER . 231 



ing capacity is doubtful, because of the resistance offered 

 by the dry soil. 



155. Texture and the capillary pull of soils. — An ingen- 

 ious method for measuring quantitatively the capillary 

 pull exerted by a moist soil has been devised by Lynde 

 and Dupre. 1 The apparatus consists of a glass funnel 

 joined to a thick-walled capillary tube by means of a piece 

 of rubber tubing, a water seal being used at this point. 

 The lower end dips into mercury. The soil to be studied 

 is placed in the funnel, and after being saturated is con- 

 nected by means of a wick of cheesecloth or filter paper 

 to the water column previously established in the capil- 

 lary tube. If no break occurs between the soil and the 

 capillary water column, the apparatus is ready for use. 



The excess water having drained away, there is a 

 thinning of the films on the soil surface due to evapora- 

 tion. Equilibrium adjustments now take place, which 

 result in the drawing upward of the water column. The 

 mercury follows, and the strength of the pull may be meas- 

 ured by the height of the mercury column. The old 

 method of measuring capillary power by the water move- 

 ment through a dry soil is vitiated by two conditions 

 — the length of time necessary, and the fact that the 

 maximum lift cannot be obtained due to excessive fric- 

 tion. This new method uses a wet soil, requires only 

 a short time, and gives a more nearly accurate idea of the 

 power of the capillary pull. It does not, however, yield 

 data regarding rate of movement, — a factor of vital 

 importance to plant growth, as will be shown later. 



Lynde and Dupre, in their results, confirm the state- 



1 Lynde, C. J., and Dupre, H. A. On a New Method of 

 Measuring the Capillary Lift in Soils. Jour. Amer. Soc. Agron., 

 Vol. 5, No. 2, pp. 107-116. 1913. 



