438 Mr, F, A, Abel on the Causes, Effects, [March 21, 



WEEKLY EVENING MEETING, 



Friday, March 21, 1862. 



The Rev. John Barlow, M.A. F.R.S. Vice-President, 

 in the Chair. 



F. A. Abel, Esq. F.R.S. 



DIKECTOR OF THB CHEMICAL ESTABLISHMENT OF THE WAR DEPARTMENT. 



On some of the Causes, Effects, and Military Applications of 

 Explosions, 



A GLANCE was taken at the general nature and causes of the 

 phaenomena termed Explosions, and attention was then specially 

 directed to those explosions which are due to chemical agency. 



In all instances of chemical action accompanied by an explosion, 

 the production and violence of the latter are either entirely or prin- 

 cipally due to the sudden and very considerable development of heat, 

 which results from the disappearance, for the time, of chemical activity. 

 The violence of such explosions is therefore regulated by the energy of 

 the chemical action, or the degree of rapidity with which the chemical 

 change takes place. There are instances in which the change of state 

 {e. g. the conversion of solids into vapours and gases), resulting from 

 chemical action and the suddenness with which this transformation 

 occurs, would suffice to produce explosive effects, quite independently of 

 the effects of heat developed by the change ; but in all such instances 

 the sudden increase in volume of the matter, resulting simply from the 

 chemical change, is insignificant as compared with the expansive effect 

 exerted, at the same time, by the heat developed in consequence of the 

 sudden and violent disturbance of chemical equilibrium. Thus, the 

 actual volume of gas produced on the decomposition of gunpowder, 

 though very considerable in comparison with that of the original solid, 

 is but small when compared with the volume which it occupies at the 

 moment of its production, when under the influence of the intense 

 heat resulting from the chemical change. 



Explosions are occasionally produced by energetic chemical com- 

 bination between elementary substances. Thus, potassium combines 

 with bromine with explosive violence, in consequence of the power- 

 fully expansive effect of the heat resulting from the intense and sudden 

 chemical action between the two elements. Again, the union of 

 hydrogen with oxygen or chlorine is so energetic, that the resulting 

 water or hydrochloric acid is suddenly and enormously expanded by 



