The Physical Character of Soils 29 



that sodium, the base of common salt, is of value to our 

 cultivated crops, though some once imagined that the soda 

 could replace the potash when it is lacking. Most experi- 

 ments, in fact, go to show that in the absence of potash 

 soda cannot take its place, and that plants will perish for 

 lack of potash even though soda is abundant. 



The element phosphorus is never found free in nature, 

 since it bums on exposure to oxygen, and in its most 

 familiar form, the heads of matches, it is used as a means 

 of producing flame. It is found in all fertile soils, and is 

 essential to the life of plants, for without some soluble 

 combination of phosphorus in the soil, no plant can 

 grow. It is removed from the soil by crops, and grazing 

 animals take it rapidly in the formation of their bony 

 structure. Hence, in all of our older cultivated soils it 

 is apt to be more deficient than any other form of plant 

 food. It is a component part of all the old rocks, and their 

 decay and disintegrations have furnished it to the soil. 

 In some sections it is found in immense deposits made up 

 of the fossil remains of the extinct animals of former 

 ages, and these deposits now form the chief source from 

 which we replenish the waste of phosphorus in our culti- 

 vated soils. 



The fossil phosphatic rock is pulverized and used to 

 some extent in that form as a fertiUzer, which slowly 

 becomes available to plants through the action of the car- 

 bonic acid in the soil water, or is dissolved in sulphuric 

 acid so that a large part of its phosphorus is made availa- 

 ble for mixture with soil water. The ancient animals 

 made their bony system from the hme and phosphorus of 

 the old vegetation, and have left the combination in the 



