1 6 THE ELEMENTS OF PLANT FOOD 



oxygen, but in some way not well understood it causes 

 the KC1O 3 to give up its oxygen at a lower temperature. 



2 KC10 3 = 2 KC1 + 3 2 



By having jars filled with water ready to slip over the 

 opening, two or three jars of O may be obtained. 



Notes. (rf) Many schools are now equipped with pneumatic 

 troughs and other chemical apparatus. Where such is the case, stu- 

 dents will not need to construct the apparatus here described. 



(<) If a large amount of oxygen is desired for class use or for other 

 purposes, it is better to buy it of those who make a business of preparing 

 it. It is shipped in strong metal cylinders into which it has been com- 

 pressed. 



Chemical Properties. Oxygen is very active chemi- 

 cally and combines with nearly every other element. 

 This combination with other elements is called oxida- 

 tion, and the products of the action are called oxides. 

 Oxidation may take place rapidly, as in the burning of 

 wood in a fire, or it may take place very slowly, as in 

 the decay of wood, the rusting of iron, or the decay of 

 the tissues of animal and vegetable matter. 



A glowing splinter of wood thrust into a jar of oxygen 

 will suddenly burst into flame and burn rapidly. This 

 is the common test for oxygen. The reaction is ex- 

 pressed : 



Carbon + Oxygen Carbon dioxide 



C + O 2 = CO 2 



The splinter will continue to burn till the oxygen is 

 used up or till the wood is entirely consumed. 



Make a little cup in the end of a piece of crayon, wrap 

 the end of a piece of wire about 8 inches in length about 



