280 Estimate of the Force of 



of the force of explosion of a mixture of oxygen and coal gas. 

 As the ignited gas expands, it loses a portion of its elasticity, 

 not only by the diminution of its density, but also by the effect 

 of the expansion on its temperature, which may be estimated 

 as altering the elasticity in the proportion of the biquadrate 

 root of that of the densities. 



Calculating upon these grounds, we find that the whole me- 

 chanical power of an explosion of 15,000 cubic feet of a mix- 

 ture of coal gas, and common air, is equal to that of the explo- 

 sion of 6 cubic feet, or 4 barrels, of gunpowder ; and if we sup- 

 pose the heated gases in both cases to escape, and mix with the 

 common air in a building containing 30,000 cubic feet, so as to 

 produce an effect commensurate to the temperature of the whole 

 mixture, the explosion of about 15 cubic feet, or 10 barrels of 

 gunpowder, would be required, in order to produce, like the gas, 

 a force of about 10 atmospheres for the whole space. It must, 

 however, be recollected, that gunpowder, thus disposed, is very 

 unfavourably situated for producing violent effects ; and that a 

 much smaller quantity, in ordinary cases, would be more for- 

 midable than the explosion of the coal gas. 



A more precise idea of the effects of such an explosion may 

 be obtained from the calculation of its projectile effects, which 

 would carry some parts of the wall of the surrounding building 

 to a height of nearly 150 yards, and others to a distance 

 of nearly 300. If the walls were in immediate contact 

 with the gasometer, the height and distance would be about 

 twice as great. But a roof of carpentry and tiles being lighter, 

 would be carried higher, while the lateral force of the explo- 

 sion would be diminished. 



Supposing the explosion of the gas to be unconfined, the 

 shock would throw down a brick wall, 9 feet high, and 18 inches 

 thick, at the distance of about 50 feet from the centre ; it would 

 probably break glass windows at 150 yards, and at 300, would 

 produce an effect similar to the instantaneous impulse of a very 

 high wind. 



CALCULATION. 



In order to compare the whole forces of expansion in a con- 



