GAS AS A FUEL 



143 



Explosions. When air is mixed with an inflammable gas, and 

 the temperature is raised to the kindling point of the gas, an explosion 

 takes place. The gas expands suddenly, sometimes with force 

 enough to blow walls or buildings apart. 



There are usually two sounds to an explosion, one caused by 

 expansion, and the other by the air rushing in. The two sounds 

 occur so close together as to give the impression of one. If there is 

 a large amount or a very small amount of gas present in the air, 

 the mixture will not explode. The proportion of air to gas in an 

 explosive mixture varies, but in general it ranges from about 5 to 12 

 parts of air to one part of gas. 



The gas of gasoline explodes when 1.5 to 3 per cent of gas is 

 mixed with air. Kerosene poured upon a burning fire often pro- 

 duces disastrous explosions because the gas and air are mixed in the 

 right proportions. Explosions in mines are due to the same cause. 



Hydrogen. Hydrogen is a colorless, odorless gas which burns 

 with a blue flame, if pure. The gas is found in coal, and also helps 

 to make up many valuable compounds, such as water, hydrogen 

 peroxide, acids, sugars, starches and many of our foods. As the 

 gas is very light, it is of great value for filling balloons. 



^HYDROCHLORIC ACID 

 FIG. 111. 



Hydrogen mixed with air is very explosive. It affords one of the 

 best examples of a gas exploding when mixed with the correct pro- 

 portion of air. 



