CAPILLARY ACTION 97 



The highest column (13! inches) was apparently saturated 

 with water to the top ; notwithstanding less water was evap- 

 orated than by the shorter columns, the water rising more 

 slowly the greater the length of the column. 



In the next experiment the height of the column was 

 in all cases fourteen inches, but the tubes were filled with 

 emery of various degrees of fineness. The trials lasted eighty- 

 four days. 



Average Diameter Water Evaporated 



of Particles. per square inch. 



0-443 mm 40-3 grams. 



0-356 ,, 1384 



0-229 155-1 



0-140 150-6 



0-076 144-7 



It will be seen that the largest quantity of water is brought 

 to the surface by the emery of intermediate fineness (diam. 

 0-229 mm.), and that as the particles become either coarser 

 or finer the quantity is diminished. The coarser particles 

 failed because the surface was never saturated with water ; 

 the coarsest emery could saturate at 8 inches, the next 

 coarsest at n inches. The finer particles failed because of 

 the slower movement of the water in their passages. Had 

 the column been shortened, one of the coarser emeries would 

 have evaporated most water; had it been lengthened one 

 of the finer would have appeared the most effective. This 

 is an important lesson. For every distance of the surface 

 from the water supply there is a particular size of soil 

 particles which will bring up the largest quantity of water, 

 and in the case of moderate distances it is by no means the 

 finest particles which are the most effective. 



The laboratory experiments on the capillary power of some 

 Californian soils made by Loughridge (California Exp. Stat. 



H 



