540 Dr. R. Hare on the Explosiveness of Nitre. 



sulphide of potassium, with carbonate and sulphate of potash. 

 The two latter are by much the more abundant products. 

 Probably sulphur is the primary and most energetic ingre- 

 dient, as when in excess it is, per se, known to be capable of 

 completely decomposing potash at a moderate heat, while 

 carbon can only partially effect an analogous change at the 

 highest heat of a furnace. Faraday has recently alleged, that 

 the production of the flame of sulphide of potassium is an 

 important agent in the explosive ignition of gunpowder. It 

 is likely that from the reaction of oxygen with sulphur and 

 potassium, a temperature results sufficiently high for the com- 

 bustion of the charcoal with oxygen, and of nitrogen with 

 sulphur and carbon, whence ensues carbonic acid and sulpho- 

 cyanogen, in union with potassium in the one case, and with 

 potash in the other. 



42. I have already distinguished the explosion of mixtures 

 like gunpowder from fulminating combinations, of which the 

 constituents, being held together by intense chemical affinity, 

 require no mechanical confinement nor impact to bring or 

 keep them sufficiently near each other for reciprocal reaction. 

 There is, however, another distinction to be made. The ex- 

 plosion of vessels by high steam is altogether the effect of heat 

 and confinement. The resulting violence, when the vessel 

 bursts, is directly as its strength ; so that, knowing how many 

 pounds per square inch the vessel was capable of bearing, we 

 know the explosive force to have been exactly equal thereto. 

 But the strength of the containing vessel, in the case of gun- 

 powder, may be very far short of that generated by the gun- 

 powder ignited within it. When held together until the tem- 

 perature is attained which is requisite for the play of affinities 

 into which the ingredients are disposed to enter, a sudden 

 evolution of heat and gaseous matter takes place, producing a 

 diruptive force far beyond the retaining power of the vessel. 



43. Although gun-cotton is a chemical combination con- 

 sisting of nitric acid and lignin, yet it does not explode, when 

 unconfined, with a violence approaching to that of other ful- 

 minating combinations above mentioned. This may be attri- 

 buted to the fact that neither the elements of nitric acid, nor 

 those of lignin, are held together by a strong affinity, and 

 consequently the forces which resist explosion are but feeble. 



Summary. 



It is an old and well-accredited maxim in chemistry, to 

 which there are but few exceptions, that fluidity is requisite 

 to chemical reaction. The fluid state, of which the necessity 

 is thus asserted, is with few exceptions attained only through 

 water, or heat, or both. In truth, however, when it is con- 



