involved in the Construction of Artillery. 183 



12. — Effect of a Heated Gun on the Charge. 



92. To this should be added the consideration, that the ignition of the 

 powder dried by the neighbourhood of the hot shot and in a warmed gun, is 

 probably much more rapid, and its effect on the gun more severe, than in ordi- 

 nary cases, from causes already and to be again adverted to. 



13. — Phenomena induced in " Quick Firing •' Limit of Heating. 



93. A train of effects, quite analogous to those described, are brought into 

 operation in very quick firing., whether with hot or cold shot, — when the interior 

 of the gun, continually receiving fresh accessions of heat from the rapidly succeed- 

 ing flashes of powder, is not given time, to transmit it by conduction, through its 

 metal to the exterior. The limit of the heat that could be conceived commu- 

 nicated from one discharge to the gun, would be the whole of that generated by 

 the ignition of the charge. Assuming the formula for gunpowder to be KO, NO5 

 -t-S-t-Cs, its atomic weight will be 135, and one part by weight will include 

 01333 of carbon. Now, Andrews (Reports, Brit. Assoc. 1849) found that one 

 part of carbon evolves as much heat in buiming as will raise an equal weight of 

 water 7900' Cent. Hence, neglecting the sulphur as not oxidized in combus- 

 tion, the heat generated by the firing of any charge of powder is sufficient to 

 raise the temperature of an equal weight of water 7900° x 0'1333 = 1053° Cent. 

 = 1895'4 Fahr., or to boil about nine times its own weight of water, or to heat 

 about nineteen times (18-945 strictly) its weight, 100° Fahr. 



94. The specific heat of water being unity, that of cast-iron (the mean of 

 those given for iron, 0'125 to 0143) is probably 0134 ; and that of gun-metal is 

 Oil (Thompson), 0'086 (Regnault). Hence, if C'be the weight of the charge 

 of powder, 141-4 C is the weight of cast-iron, and 172-3 C that of gun-metal 

 that the whole of its heat would heat 100^ If W, therefore, be the weight of 



the gun, and the heat were uniformly diffused in its mass, — 100° will be 



K yv 



172''? C 



the resulting temperature in the case of a cast-iron gun, and 100° that 



for one of gun-metal, k being a constant representing the fraction of the 



2b 2 



