Xvi GENERAL INTRODUCTION 



ounces capacity. It should have a glass delivery tube, 

 inserted through a one-holed rubber stopper, and so bent 

 as to pass under the surface of water contained in a 

 deep dish. Fill several pint fruit-jars with water, cover 

 with pieces of stiff pasteboard, and turn mouth down- 

 wards in the dish of water. From one half to two thirds 

 ounce of an equal mixture of potassium chlorate and 

 manganese dioxid (procured at drug store) is put in the 

 flask and heated by means of a gas or alcohol lamp. 

 When the oxygen begins to form, collect some in jars 

 by inserting the end of delivery tube under the jars as 

 they stand in water. Caution: Remove delivery tube 

 from water before cooling the flask, to prevent any water 

 being drawn back. 



Oxygen and the Air. The great activity of pure oxygen 

 in attacking other substances can be shown by passing 

 into a fruit-jar a lighted splinter, a piece of lighted mag- 

 nesium ribbon, an old watch spring (or a bit of picture 

 wire), the end of which has been dipped in sulfur and 

 lighted. About one fifth of the air is oxygen and about 

 four fifths is nitrogen and other inactive gases. Pure 

 nitrogen will quickly extinguish a lighted splinter thrust 

 into it. It is the oxygen in the air that supports all forms 

 of burning. Less than one half of one per cent of the 

 air is an inactive gas called carbon dioxid, a compound 

 of carbon and oxygen. It is formed not only when wood 

 or coal is burned, but also by the life processes of animals 

 and plants. 



Oxidation. That something besides wood or coal is 



ecessary to a fire can be shown by shutting off entirely 



e draught of a stove. Fire and other forms of combus- 



depend on a process called oxidation. This consists 



m the uniting of oxygen with other substances. When 



