ELEMENTS NECESSARY FOR PLANT GROWTH 33 



of three volumes of the gas to one hundred volumes of the 

 liquid. Fish and other marine life are dependent upon 

 this oxygen dissolved in the water. With very few excep- 

 tions oxygen forms compounds with all the other ele- 

 ments; in this respect no other element can compare with 

 oxygen. 



The activity of oxygen in forming chemical combina- 

 tion is remarkably increased by raising its temperature. 

 Many substances that resist any except very slow oxidation, 



FIG. 6. Preparation of oxygen in the laboratory. 



when heated in the air, will unite with oxygen so rapidly 

 that they suffer combustion. This is remarkably apparent 

 when a building in conflagration is entirely consumed in 

 a short time. Oxygen is absolutely essential in the build- 

 ing up of plant tissues. The carbohydrates, the proteids, 

 and the fats, the constituents of plants that give to them 

 their value as foods, are composed in large part of oxygen. 



In the process of decay and in the disposal of sewage, 

 oxygen plays a beneficial role, decomposing germs that, 

 if allowed to multiply, would produce epidemic diseases. 



