HYDROGEN 99 



exercised not to bring a flame near a mixture of oxy- 

 gen and hydrogen, for if the mixture is lighted an 

 explosion will surely follow. So every care must be 

 taken to free the hydrogen from air before it is 

 lighted. 



Properties. Hydrogen is a colorless, odorless, taste- 

 less gas. It is the lightest known gas and because of this 

 fact it is used as the standard of weight by which all 

 gases are measured. In speaking of the weight of any 

 other gas it is spoken of as being so many times as 

 heavy as hydrogen. Thus air is 14.4 times as heavy, 

 and oxygen 16 times as heavy as hydrogen. It com- 

 bines readily with oxygen, burning with a pale blue 

 flame. If a burning splinter be brought to the mouth 

 of an inverted bottle of hydrogen, a slight explosion 

 will occur and a pale blue, almost invisible flame 

 will burn upward into the bottle. This is the test of 

 hydrogen. If the burning splinter is thrust quickly 

 into the hydrogen an explosion occurs at the mouth 

 of the bottle, but the flame on the splinter will be 

 extinguished. This shows that hydrogen will burn, 

 but will not support combustion. 



Although it is not poisonous to breathe hydrogen, 

 one could not live long with only hydrogen, as oxygen 

 is necessary to life. 



Uses. Because of its lightness, hydrogen is used 

 sometimes in filling balloons, though hot air and coal 

 gas are more frequently used because they are 

 cheaper. In recent years hydrogen has been used in 



