involved in the Construction of Artillery. 273 



appears to wait on heavy cast-iron guns, due (as already explained) to the local 

 internal strains induced by the condensation of the metal at the interior of the 

 chase, must with gun-cotton be greatly accelerated. On the other hand, the 

 heat evolved is much less from gun-cotton than from gunpowder, and hence 

 less powerful internal strains from unequal expansion of the gun. 



30. — Material of the Gun in relation to Chemical Action of the Charge. 



253. Sulphuret of potassium, converted in great part while in a nascent state 

 instantly by oxidation into sulphate of potass, and water, appear to be the main 

 agents, resulting from the decomposition by ignition of gunpowder, capable of 

 acting destructively upon the gun. In the case of gun-cotton, nitric acid and 

 water are the agents in a like predicament. 



254. Water, combined with or acting along with air, as is always the case 

 here, reacts with rapidity in corroding iron and cast-iron, the extent of which, 

 for unit of surface and in relation to time of action, have been given very fully 

 in the author's researches on the Corrosion of Iron (Trans. Brit. Assoc. 1840); 

 but neither air nor water, nor both, have a very appreciable corroding action 

 upon gun-metal. 



255. Upon all three, cast-iron, wrought-iron, and gun-metal, the oxidized 

 compounds of sulphur, as well as the alkaline sulphurets, act with rapidity, 

 perhaps more destructively upon guu-metal than on either of the other metals, 

 producing a form of local corrosion that eats the metal into pits and small 

 cavities, not unusually found in the interior of old guns. 



256. The most formidable chemical re-action, however, produced in any 

 species of ordnance is that by which the vents, and portions of the interior of the 

 chase near the seat of the shot, become so much enlarc'ed in continued firin^ 



? DO 



from cast-iron guns. This, which has been always attributed solely to gradual 

 rending off and blowing away mechanically of minute successive fragments of the 

 metal from the neighbourhood of the vent, by each discharge, is in fact a veri- 

 table deflagration of the uncombined graphite contained in the cast-iron, and 

 of the metal itself (See Note D.) The carbon first, the metal itself directly 

 afterwards, burn just as the carbon of the powder itself does, and the remaining 

 metal, rendered soft and porous whei'e this occurs by the initiatory burning 



