CHAPTER XIII. 



OXYGEN, HYDROGEN AND WATER. 



OXYGEN is a colorless, odorless, tasteless gas that constitutes 

 nearly one-half the weight of the solid crust of the earth, eight- 

 ninths of the water, one-fifth of the air, and enters largely into 

 the composition of all vegetable and animal bodies. Its symbol 

 is 0, and its combining weight 16. While it is so abundant, so 

 important in every way, it was not known, or isolated so that 

 its properties could be studied until the year 1774. Its discovery 

 marks an era not only in the growth of chemical science, but in 

 the progress of human affairs. 



Oxygen may be prepared by heating crystals of potassium 

 chlorate in a test tube over a spirit flame; it soon melts into a 

 clear liquid which presently begins to boil from the escaping 

 bubbles of gas. That the gas is oxygen may be shown by 

 thrusting into the tube a stick whose end is a glowing coal, when 

 it will burst into flame, burning with great vigor. Any substance 

 that burns in air burns much more rapidly in oxygen. Take a 

 piece of wire and wind about one end of it a piece of twine 

 and soak the twine in melted sulphur, then ignite the sulphur 

 and thrust the wire into a jar of oxygen, the burning sulphur 

 ignites the iron, which burns brilliantly as long as the oxygen 

 lasts. 



Another very common method of preparing oxygen in a small 

 way, is from the red oxide of mercury, which yields, when heated, 

 the liquid mercury and the gas oxygen. If the oxide be weighed 

 carefully, and after the decomposition the mercury and the 

 oxygen are weighed, their weight will be found to be equal to the 

 original weight of the oxide, which is thus shown to have con- 

 tained only oxygen and mercury in chemical combination. The 

 heat applied overcame the force of chemical attraction and the 

 (106) 



