Estimate of the Force of Explosion of Coal Gas. 271^ 



Dr. Henry has found (Phil. Trans. 1808), that good coal gas 

 requires for its combustion, about twice its bulk of oxygen gas, 

 and affords a little more than its bulk of carbonic acid. Now 

 since common air contains only 21 per cent, of oxygen, it can 

 combine with no more than 12 per cent, of coal gas; so that 

 112 parts of the mixture contain but 33 of substances capable 

 of aftbrding heat, while the remainder tends, in some measure, 

 to impede their union. Hence we cannot suppose the heat, 

 thus generated, to exceed about J- of the heat which would be 

 excited in a mixture of the gas with pure oxygen. And we 

 shall probably exceed the truth, in allowing to the combustion 

 of such a mixture, a heat equal to that which is evolved in the 

 deflagration of gunpowder; which is sufficient, upon the most 

 probable estimate, to increase in the ratio of 1 to 80, the natu- 

 ral elasticity of the fluids generated, which amount to 250 times 

 the bulk of the powder, so that the elasticity, thus augmented, 

 becomes equal to 20,000 atmospheres. It is true, that some of 

 the soHd substances contained in gunpowder may possibly be 

 converted into vapour, and may contribute to its effect : but 

 we have no sufficient reason to believe that the vapours of any 

 of these substances would be more elastic than air ; and Count 

 Rumford's hypothesis, concerning the effect of steam, is every 

 way inadmissible; since even if nitre contained water of cry- 

 stallization, its vapour would be little more effectual than an 

 equal weight of the gaseous substances. 



We may, therefore, suppose the exploding mixture to acquire 

 a degree of heat, capable of increasing its elasticity in the ratio 

 of 1 to 20. Dr. Ingenhousz, following Robins, makes the ex- 

 plosive force of a mixture of oxygen and hydrogen equal to 4 

 atmospheres only : but the assumption of a degree of heat equal 

 only to that, which Robins obtained in a fire, is wholly arbitrary : 

 and a single drop of ether, in a bottle of oxygen, appears to 

 have exploded with a force much more than commensurate to 

 such a cause. On the other hand, when we consider with what 

 safety a mixture of oxygen and hydrogen may be made to ex- 

 plode in a common quart bottle of green glass, we cannot hesi- 

 tate to allow that 80 atmospheres must be a very ample estimate 



