48 THE CULTURE OF FARM CROPS. 



Silver 



Copper 



Lead 



Arsenic 



Silica 



Bitumen 



Organic matter 34.59 



Total in one gallon 13489.17 grains. 

 Per cent. 19.73 



The water of springs, wells and rivers is thus never pure,, 

 but holds in solution more or less of solid substances. Hence 

 we find that land watered by irrigation from rivers produces 

 much larger crops than that watered by rain ; also that land 

 that has been or is periodically overflowed by floods, becomes 

 exceedingly fertile. Even rain water is not pure except in 

 the wettest seasons, when the atmosphere has been washed 

 clean from its impure matter which is brought down by the 

 showers. In this way a large quantity of solid fertilizing 

 matter, as well as of fertilizing gases, is brought within reach 

 of the roots of the plants by the rain which is absorbed by 

 the soil. The water also dissolves matter from the soil and 

 presents it to the roots in such a condition that it can be 

 absorbed and utilized as nutriment, 



These facts prove how indispensable it is that the soil should 

 be brought by thorough culture, and the use of the most perfect 

 implements, into such a condition of porosity and mellowness 

 that the water may be absorbed and held in it and not flow off 

 from the surface and carry away into the streams, not only all 

 its own burden of rich fertilizing matter but also rob the xoil 

 of a large portion of its own possession. 



The solvent power of water is increased by heat, in regard 

 to nearly all subetrnces excepting lime and ammonia which 

 are dissolved r.nd absorbed by cold water more readily than 

 by warm. This property will be further explained in a 

 future chapter on HEAT. 



Water has a strong affinity for various substances, indeed 

 it exists in a greater or less proportion in almost all solid 

 bodies and in every crystallized substance ; forming in these 

 cases what is known as "the water of crystallization." 



When limestone is burned, water and carbonic acid are 



