20 



THE ELEMENTS OF PLANT FOOD 



The H will burn quietly as it escapes, or it may 

 explode with a harmless puff. In either case water 

 is formed (2 H 2 + O 2 = 2 H 2 O). 



Chemical Properties. Hydrogen will not combine 

 with all other elements. It combines readily with O 

 and has a strong affinity for chlorine (Cl). In direct 

 sunlight H unites with Cl with explosive violence, 

 in diffused light quietly, and in darkness not at all. 

 When the combination takes place, hydrochloric acid 

 (HC1) is formed. Burning H produces one of the 

 hottest flames known. 



NITROGEN (N) 



Description and Occurrence. Free nitrogen is a 

 colorless, odorless gas. It is one of the constituents 

 of air, forming four fifths of it. It is very unlike oxygen. 

 O is active, N is inert. N hinders the activity of O. 

 O sustains life, free N has no physiological effect. O 



combines with most ele- 

 ments, N combines with 

 very few. Nitrogen in 

 combination with other 

 elements is found in niter 

 (saltpeter), from which it 

 gets its name, and other 

 nitrates. It is found 

 also in ammonia, in flesh, 

 in hair, and in all vege- 

 tables and grains. 

 FIG. 6. Preparing Nitrogen. Preparation. The 



air contains the two elements O and N free, and an easy 

 way to obtain the N is to remove O from the air; this 



