XVI GENERAL INTRODUCTION 



Water also makes paper semi-transparent, but it soon 

 evaporates : fat does not evaporate. 



Another test for fats is to mount a thin section of the 

 endosperm of castor-oil seed in water and examine with 

 high power. Small drops of oil will be quite abundant. 

 Treat the mount with alcanin (henna root in alcohol). 

 The drops of oil will stain red. This is a standard test for 

 fats and oils. 



To make or liberate Oxygen. — If there is a chemistry 

 class in school, one of its members will doubtless be glad 

 to prepare some of the gas called oxygen, and furnish 

 several glass jars filled with it to the biology class. If it 

 is desired to make oxygen, the following method may 

 be employed : Provide a dry glass flask of three to 

 four ounces capacity. It shouM 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 

 downwards in the dish of water. From one half to 

 two thirds ounces 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 pre- 

 vent any water being drawn back. 



Oxidation. — That something besides wood or coal is 

 necessary to a fire can be shown by shutting off entirely 

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

 tion depend on a process called oxidation. This consists 

 in the uniting of oxygen with other substances. When 



