THE ELEMENTS THAT PLANTS USE 55 



I4^2times lighter than air (hence its use in filling bal- 

 loons) and over 11,000 times lighter than water. 



Hydrogen is tasteless, odorless, and colorless; and 

 incapable of supporting life, although not poisonous. It 

 is combustible combines with oxygen and develops light 

 and heat. It is very abundant, being an ingredient of 

 many organic and inorganic substances. 



A few of its combinations are : 



1. With oxygen it forms water. 



2. With chlorine it forms hydrochloric acid. 



3. With sulphur and oxygen it forms sulphuric acid. 



4. With nitrogen and oxygen it forms nitric acid. 

 We also find hydrogen in organic substances protein, 



starch, fat, fiber, etc. 



Nitrogen: the most costly of purchased plant foods. 

 In appearance nitrogen in no way differs from the atmos- 

 pheric air, of which it is the main' ingredient (four-fifths 

 of the air is nitrogen). Hence we know it to be without 

 color, taste, or odor. In weight it is somewhat lighter 

 than atmospheric air. It may be described as negative 

 in its properties, for it is not combustible, nor is it a 

 supporter of combustion. It somewhat dissolves in 



THE GREATER PART OF THIS WONDERFUL CROP COMES FROM THE AIR 



water, and its combining powers are very slight. While 

 nitrogen is present in the air in large amounts it lends 

 itself to the use of plants in exceptional cases, only, the 



