302 



THE IRRIGATION AGE. 



the dew descends and is absorbed, and the waters of 

 irrigation poured upon the ground quickly disappear. 

 But after much water falls upon the earth the latter be- 

 comes saturated, can hold no more, and the surplus 

 runs off the surface or sinks down through until it 

 reaches the water table. This happens more speedily 

 in some soils than in others. Thus, 100 pounds of dry 

 soils, as here specified, will hold the quantity of water 

 set opposite their respective names without dripping or 

 running off. 



Quartz sand 25 pounds 



Calcareous sand 29 pounds 



Loamy soil 40 pounds 



Clay loam 50 pounds 



Pure clay 70 pounds 



But dry. peaty soils and adobe will absorb a much 



evaporation of ammonia under pressure. Ether, chloro- 

 form, alcohol, and numerous other substances, produce 

 a sensation of cold when Tubbed on the skin, which is 

 not due to anything in those substances, but wholly to 

 their rapid evaporation or volatility. The presence of a 

 saturation of water in the soil, however, excludes the 

 air in a great degree and thus is injurious to plants, 

 whose roots must have air as well as moisture, hence 

 the necesity for drainage where there is a liability to 

 saturation. 



Unless rain or dew is falling or the air is saturated 

 with moisture, watery vapor is constantly arising from 

 the surface of the earth. The fields, after the heaviest 

 rains and floods gradually become dry, and this takes 

 place more rapidly in some fields or parts of fields than 

 in others, in fact, wet and dry patches of ground may be 



PUBLIC BUILDINGS, OGDEN. UTAH. 



18. Sacred Heart Academy. 



16. State School of Deaf, Dumb and Blind. 



larger proportion before becoming saturated to the drip- 

 ping point; sometimes such soils will absorb their own 

 weight of water. Arable soils generally will hold from 

 forty to seventy per cent of their weight of water. 



This power of retaining water renders such a soil 

 valuable in dry climates. But the more water the soil 

 contains in its pores the greater the evaporation and 

 the colder it is likely to be. Indeed, evaporation is a 

 source of cold, sometimes to so great a degree that ice 

 will be formed. In very hot regions in India where 

 ice is inacessible it is customary to place small, shallow 

 saucers filled with water on the ground after nightfall, 

 and they are gathered in the morning before sunrise, 

 the water being converted into ice by the rapid evapora- 

 tion from the soil during the night. Our modern ice 

 machines owe their efficacy for making ice to the rapid 



15. Industrial Building of State School, for 

 U. City Hall. .Deaf, Dumb and Blind. 



17. State Industrial School. 



seen on the same field, indicating a heavy or light soil. 

 Generally speaking, those soils capable of containing 

 the largest portion of the rain that falls also retains it 

 with greater obstinacy and require a longer time to 

 dry. The same thing happens when the land is irri- 

 gated. Thus, sand will become as dry in one hour as 

 pure clay in three, or peat in four hours. 



There is one fact every irrigator should constantly 

 bear in mind and that is: Water saturation of the soil 

 is never necessary to plant life; it is, in fact, positively 

 injurious except in the case of acquatic plants. A long 

 time ago men, seeing rice growing luxuriantly in 

 swamps, imagined that plant would not grow anywhere 

 else, and, accordingly, rice culture meant a swamp. But 

 it was discovered that rice would grow better and pro- 

 duce a larger and richer crop in arable soil generally, 



