CAPILLARITY yg 



(5) Nitrate of soda solutions of similar strengths. 



(6) Soil extract. 



Soil extract. — The soil extract is prepared as follows : 

 Ten grams of the soil are rubbed up with 15 to 20 c.c. 

 of distilled water, and allowed to stand for twenty-four 

 hours with frequent stirring. Any fine particles not 

 removable by filtering may be neglected, even if the 

 solution is turbid. The radius of the capillary tube is 

 obtained from the weight of a thread of mercury filling 

 a measured length. If /= length of mercury thread, and 

 z£/ = weight of mercury, then r, the radius of the tube, 



-v; 



w 



13-59 Xtt/. 



The surface tension (T) of the various solutions is 

 obtained approximately from the formula — 

 ^ _ Mr 

 ~ 2 

 where h is the height of the liquid in the tube in 

 centimetres and d is the density of the solution. The 

 result is obtained in dynes. 



59. Capillary Attraction in Soils. 



Long glass tubes of 1-2 cm. in diameter and 

 graduated in centimetres, should be used for this deter- 

 mination. The lower end of each tube is closed with a 

 piece of linen, and the " fine earth " of the soils under 

 examination filled in little by little with gentle tapping 

 on the bench for compacting. 



The tubes, after filling, are supported in an upright 

 position in a vessel containing water (Fig. 14), the 

 linen-covered ends dipping to the depth of 2 cm. 

 The height of the water is measured at stated intervals, 

 and the results for the various soils plotted out 

 graphically. The observations may be discontinued 



