TEE MAIN TYPES OF SOIL 49 



condition is always accompanied by the 

 disappearance, in an easily perceptible form, 

 of heat, This result can be readily illustrated 

 in a variety of ways. If, for instance, we 

 moisten the back of the hand and then blow 

 upon the moistened surface, so as to cause 

 rapid evaporation, we notice that the skin 

 is manifestly cooled to a greater extent than 

 would be the case were the moisture allowed 

 to evaporate more slowly. A flask containing 

 liquid can be kept cool in hot weather by 

 surrounding it with some absorptive material 

 like flannel, and if this be saturated with water, 

 the latter will evaporate when freely exposed 

 to the air, and the withdrawal of heat from 

 the liquid in the flask will be indicated by a 

 fall in temperature. 



During dry weather, when water is removed 

 from sand by evaporation or otherwise, the 

 soil does not shrink to any great extent, and, 

 consequently, sandy soils never show cracks 

 during periods of drought. Owing to the 

 comparatively small amount of water that 

 sand can take up and retain, and also because 

 of the ease with which it parts with moisture, 

 crops are apt to ripen prematurely on such 

 soil and are always deficient in yield during 

 seasons of low rainfall. Other things being 

 equal, therefore, sandy soils give their best 



