12 Agricultural Chemistry. 



Phosphorus (P) always occurs in a state of combination. 

 Phosphorus compounds, chiefly phosphates, are very widely dis- 

 tributed, but in small proportion, in the rocks of the earth. De- 

 posits of calcium phosphate occur in certain localities and are 

 one of the chief sources of our phosphate fertilizers. All fertile 

 soils contain small quantities of phosphates, which are taken up 

 by plants and through plants find their way into animals, where 

 they accumulate in the bones or other hard parts, as teeth and 

 shells. 



The element phosphorus, as usually prepared, is a yellowish 

 waxy substance, which has the power of emitting a faint light 

 when exposed to the air. This property was the origin of its 

 name, which is derived from the Greek and means "the light 

 bearer. " The emission of light is due to slow combination with 

 the oxygen of the air, resulting in the production of heat. 



Phosphorus is a violent poison. It is largely used in the man- 

 ufacture of lucifer matches and rat-poison. For the farmer its 

 chief importance lies in the use of its compounds, the phosphates, 

 as fertilizers, and its occurrence in certain fats and protein com- 

 pounds of feeding stuffs and in the bodies of animals. 



Soils are quite liable to be deficient in phosphates, as the latter 

 are largely drawn upon by many crops, particularly grain crops, 

 4^re the phosphorus accumulates in the seed and is sold from 

 the farm. 



Calcium (Ca) is very abundant in nature, always occurring in 

 a combined state. Calcium carbonate is found in enormous quan- 

 tities, as chalk, limestone and marble, and contains the three ele- 

 ments, calcium, carbon and oxygen. It also occurs as gypsum, a 

 compound of calcium, sulphur and oxygen. The element itself 

 is an easily oxidisable metal, difficult to prepare, and of no im- 

 portance to the farmer. Its oxide, or a compound of calcium and 

 oxygen, is the important substance, quick lime. This is made by 

 burning limestone, whereby the carbon and part of the oxygen 

 are removed as a gas. Calcium is an essential constituent of 



