28 HOW CROPS GROW. 



Albumin, globulin, casein and similar principles, never 

 absent from plant or animal, possess also a small con- 

 tent of sulphur. In hair and horn it occurs to the amount 

 of three to five per cent. 



When organic matters are burned with full access of 

 air, their sulphur is oxidized and remains in the ash as 

 sulphates, or escapes into the air as sulphur dioxide. 



Phosphorus is an element which has such intense af- 

 finities for oxygen that it never occurs naturally in the 

 free state, and when prepared by art, is usually obliged to 

 be kept immersed in water to prevent its oxidizing, or 

 even taking fire. It is known to the chemist in the solid 

 state in two distinct forms. In the more commonly oc- 

 curring form, it is colorless or yellow, translucent, wax- 

 like in appearance ; is intensely poisonous, inflames by 

 moderate friction, and is luminous in the dark ; hence its 

 name, derived from two Greek words signifying light- 

 bearer. The other form is brick-red, opaque, far less in- 

 flammable, and destitute of poisonous properties. Phos- 

 phorus is extensively employed for the manufacture of 

 friction matches. For this purpose yellow phosphorus is 

 chiefly used. When burned in air or in oxygen gas this ele- 

 ment forms a white substance phosphorus pentoxide 

 (formerly termed anhydrous phosphoric acid) which dis- 

 solves in water, at the same time uniting chemically with 

 a portion of the latter, and thus yielding a body of the 

 utmost agricultural importance, viz., phosphoric acid, 



EXP. 18. Burn a bit of phosphorus under a bottle, as in Exp. 8, omit- 

 ting the water on the plate. The snow-like cloud of phosphorus pen- 

 toxide gathers partly on the sides of the bottle, but mostly on the plate. 

 It attracts moisture when exposed to the air, and hisses from develop- 

 ment of heat when put into water. Dissolve a portion of it in hot 

 water, and observe that the solution is acid to the taste. Finally evapo- 

 rate the solution to dryness at a gentle heat. Instead of recovering 

 thus the white opaque phosphorus pentoxide, the residue is a trans- 

 parent mass of phosphoric acid, a compound of phosphorus, oxygen 

 and hydrogen. 



In nature phosphorus is usually found in the form of 



