246 On the Heat produced by firing Gunpowder, fyc. [Oct. 



evolved in the combustion of gunpowder, its quantity is not 

 nearly so great as has been imagined. Again, if we consider 

 that the products of the combustion of gunpowder have not, by 

 direct experiment, been proved to have a greater specific heat 

 than the ingredients of that composition, the phenomenon of 

 heat being produced during that combustion should not be urged 

 as an objection to the hypothesis of Black and Crawford. 

 Indeed, it appears very probable, from the inspection of the 

 Table of Specific Heats of Different Bodies, that those elastic 

 products have a less capacity than the ingredients of gunpowder 

 from which they are produced. For example, azote, which 

 composes two-thirds of the elastic products, has a capacity of 

 2669, and carbonic acid, comprising one-third of the products, 

 if my experiments are to be trusted to, has a capacity of only 

 1751, water being 10000. Nitric acid, of a specific gravity of 

 1354, has a capacity of 5760. The azote, therefore, and oxygen, 

 which is produced from the decomposition of one of the ingre- 

 dients forming the elastic products of not half the specific heat 

 of that ingredient, should, according to the hypothesis of Black, 

 evolve heat. This might take place even if we make allowance 

 for the lesser capacity which nitric acid has in its state of one 

 of the ingredients of the nitrate of potash. 



The same condition of potential compression may also contri- 

 bute to the intense heat which takes place in a blast-furnace. 

 This heat is known by all conversant with the phenomenon to be, 

 not in a ratio of the fuel consumed, but of some compound ratio. 

 This may be explained in the following manner : 1. A quantity 

 of air is forced into contact with the coals in a state of ignition, 

 and its temperature is suddenly raised extremely high. 2. In 

 this condition, were it not for the pressure of the atmosphere, it 

 would become as suddenly expanded. 3. Had this expansion 

 taken place, it would have acquired an increased capacity, and 

 would consequently have absorbed a considerable portion of the 

 caloric evolved by the combustion, tending thereby to lessen the 

 capacity of the heat. 4. But the heated air being prevented by 

 the pressure of the atmosphere from expanding in a ratio equal 

 to the temperature acquired, the absorption of caloric is lessened, 

 and a greater proportion of the heat of combustion is rendered 

 free. Thus, although the total quantity of caloric evolved at, 

 and consequently to combustion, may be in a direct ratio of the 

 quantity of fuel consumed ; yet the intensity of the thermome- 

 trical heat at the moment, and at the place of combustion, will 

 be greater in a compound ratio, directly as the pressure of the 

 atmosphere, and inversely as the times of expansion of the air 

 employed in the blast. These times are, of course, inversely as 

 the intensity of the blast. The thermometrical heat then, at the 

 moment and place of combustion, will be in a compound ratio of 

 the quantities of fuel consumed, the weight of the atmosphere, 



