80 THE TEXTURE OF THE SOIL [chap. 



tion of its water content, much trouble would be 

 necessary, and a long time must elapse before equili- 

 brium could be obtained in the long tube filled with 

 wet soil. Practically, however, the same result can 

 be reached with the apparatus previously described 

 for estimating the maximum capacity of the soil for 

 water, by constantly bringing the thin layer of soil 

 there used into contact with dry soil, until the 

 previously saturated soil no longer parts with water 

 to the new soil. 



After the determination of maximum water capacity, 

 as previously described (p. 6y\ a little more fine earth, 

 which has been standing for some time over water in a 

 closed space so that it has acquired all the hygroscopic 

 moisture it can, is shaken lightly over the surface of the 

 wet soil in the box to the depth of \ inch or so. It 

 rapidly becomes wet, as will be evident by a change in 

 colour, whereupon it is struck off by drawing a fine 

 tightly stretched wire across the top of the box and 

 shaking the loosened layer off. More fine earth is then 

 shaken on and struck off as before when wetted, the 

 operation being repeated again and again, until a thin 

 dry layer remains on the surface for half an hour or so 

 without showing by change of colour any absorption of 

 water. During this wait the box should be in a closed 

 chamber over water. With fine-grained clays and loams 

 the process does not take long, with a coarse sand the 

 water moves slowly into the dry layer, and it is difficult 

 to hit off the exact end-point, when the soil particles 

 are still surrounded by water but the surface tension 

 is too great to allow this water to pass into dry soil. 

 Finally, the box and its contents are weighed, dried 

 in the oven, and reweighed. The second weighing 

 when dry is necessary, because the box will be found 

 to hold more dry soil than was originally filled into 



