PLYMOUTH INSTITUTION. 189 



be dangerous and refused to introduce it into their houses for 

 fear of being blown up or burnt, but he remarked that as time 

 and the actual observation of facts were the best means of dis- 

 pelling unfounded prejudice, these opinions were now very nearly 

 obliterated ; gas being found to be infinitely safer than either 

 candles or lamps. 



After the lecturer had read his paper, he proceeded to show 

 a number of experiments with a view to exemplify more parti- 

 cularly the nature and properties of Coal Gas; and the cir- 

 cumstances under which explosions take place. He first explained 

 that, in cases of combustion, two bodies are concerned, one the 

 inflammable body which is to be burned, and the other the oxygen 

 gas of the atmosphere ; without combining with which the in- 

 flammable body will not burn : oxygen then is called the supporter 

 of combustion. Now, as coal gas kept from contact with the air 

 does not contain any of this supporter of combustion in itself, it 

 consequently cannot burn. 



This he proved by taking a vessel full of coal gas, and introducing 

 into it a lighted candle, which was immediately extinguished; 

 thus showing that the Coal Gas would neither burn of itself, nor 

 allow any body to burn in it when unmixed with air ; but he 

 afterwards showed that by mixing a portion of air witl) the gas 

 contained in the receiver, combustion would take place rapidly ; 

 for, on introducing the lighted candle again, the whole flashed ofl' 

 with an explosion. Gas is only delivered in a stream from a jet 

 and consequently can only burn as fast as it can come in contact 

 with the air; but if a large quantity of gas and atmospheric 

 air be previously mixed and a light be applied, the whole will 

 take fire at once with an explosion, in consequence of every part 

 of the gas being in contact with a portion of a supporter of com- 

 bustion. But the force of this explosion varies according to the 

 proportion of gas and air, because if there be more of either than 

 is just sufficient to saturate the other, the superfluous quantity 

 reduces the violence of the explosion. 



Chemists had stated that 12 parts of atmospheric air and one 

 of coal gas produced the maximum of effect; but the lecturer 

 had always found in the course of his experiments that the greatest 

 effect was produced by a mixture of 9 of air to one of gas ; this he 

 exemplified by using an instrument, which he called an ex- 

 plodimeter, in which gas was mixed with air in different pro- 

 portions ; which, by means of a graduated scale on the instrument, 

 could be ascertained vei*y accurately. The expansion produced 

 by the explosion of these mixtures was made to act on a valve 

 which was blown to different heights on a graduated stem, ac- 

 cording to the force of the explosion, and it was here found tliat 

 the proportions stated by the lecturer produced the greatest 

 effect. 



The lecturer concluded by explaining the circumstances under 

 which explosions usually take place in dwellings, together with 



