133 HOW CROPS GROW. 



When organic matters containing sulphur — ae hair, 

 albumin, etc. — are burned with full access of air, this 

 element remains in the ash as sulphates, or is partially 

 dissipated as sulphur dioxide. 



IHOSPHORtrS AND ITS COMPOUNDS. 



Phosphorus, Sym. P, at. wt. 31, has been sufficiently 

 described (p. 2^)? Of its numerous compounds but two 

 require additional notice. 



Phosphorus Pentoxide, Sym. PaOj, mo. wt. 142, 

 does not occur as such in nature. When phosphorus is 

 burned in dry air or oxygen, anhydrous phosphoric acid 

 is the snow-like product (Exp. 18). The term "phos- 

 phoric acid," as now encountered in fertilizer analyses, 

 has reference to "anhydrous phosphoric acid," as phos- 

 phorus pentoxide was formerly designated. Phosphorus 

 pentoxide has no sensible acid properties until it has 

 united to water, which it combines with so energetically 

 as to produce a hissing noise from the heat developed. 

 On boiling it with water for some time, it completely dis- 

 solves, and the solution contains— 



Phosphoric Acid, Sym. HsPOi, 98. — The chief in- 

 terest which this compound has for the agi-iculturist lies 

 in the fact that the combinations which are formed be- 

 tween it and various \)?iBQS— phosphates — are among the 

 most important ingredients of plants and their ashes. , 



When organic bodies containing phosphorus, as le- 

 cithin (p. 132), and, perhaps, some of the albuminoids, 

 are decomposed by heat or decays the phosphorus appears 

 in the ashes or residue, in the condition of phosphoric 

 acid or phosphates. 



The formation of several phosphates has been shown in 

 Exp. 30. Further account of them will be given under 

 th.e metals. 



CHLORINE AND ITS COMPOUNDS. 



Chlorine, Sym. 01., at. wt. 35.5. — This element exists 



