in Edinburgh, on the L 2M March 1825. 85 



readers may fully comprehend the true cause of this explosion, 

 and may appreciate the real amount of the danger which is 

 supposed to attend the use of gas, we beg their attention to 

 the following observations. 



As gas itself is not an explosive substance, and as it is not 

 compressed in any of the pipes by which a house is supplied, 

 it is impossible that any explosion can take place within the 

 pipes, even if the gas were by any accident set on fire. Even 

 if a room were filled with pure gas, the gas would not explode, 

 though a lighted candle, or a piece of red-hot iron were placed 

 in the middle of it. Gas becomes explosive, and consequently 

 dangerous, only when it is mixed with a certain proportion of 

 atmospheric air. It is then called an explosive mixture, and 

 may be exploded by carrying a lighted candle into the middle 

 of it. The proportion of atmospheric air necessary to render 

 gas explosive, depends on the nature and qualities of the gas, 

 and it may be said in round numbers to vary from three-fourths 

 to fourleen-ffteenths, that is, there must be from l-4rA to 

 \-\5th of gas in the mixture to render it explosive. 



In order that an explosive mixture of gas and air may be 

 formed, it is necessary that the stop-cocks which let off the 

 gas should be left open for a great length of time ; that there 

 should be no change of air in the apartment; and that a light- 

 ed candle should be brought into it after the mixture had 

 become explosive, and before it ceases to be so. All these 

 circumstances must be combined before an explosion takes 

 place. With regard to the first, we can conceive nothing 

 more unlikely to happen. We never hear of a servant leav- 

 ing open a water-cock and inundating the house, though 

 there is no personal danger to himself in committing the 

 fault. In the case of the gas, the servant knows that by 

 his carelessness he is exposing himself to the chance of an 

 accident;— but admitting that his carelessness is such as to 

 overlook this consideration, and that he has left open the stop, 

 cock* the gas flows slowly out, and must flow for very many 



• The difficulty of leaving open a gas- cock, by mere carelessness, is very 

 considerable. As the lights are put out by shutting the gas-cock, it must 

 necessarily be shut before the flame disappear, and it is not to be supposed 

 that any servant will turn it back. Those who are so shamefully ignorant 



