involved in the Construction of Artillery. 267 



238. With steel guns, reduced in scantling at all in proportion to their 

 assumed resisting powers, fracture would, in all probability, follow llie stroke of 

 shot ; the latter being shattered, also, into a formidable "mitraille" against the gun. 

 The chances of this are much less with cast-iron, and less again with wrought- 

 iron. If the mass of the wrought-iron gun, remain not very much reduced 

 below that of a cast-iron gun for equal caliber, there is no reason to suppose it 

 would be more liable to injury than the cast-iron gun. But, if the relative mass 

 of metal for the same caliber were seriously reduced, as niiglit be done witli 

 wrought-iron field guns, of equal resisting powers with existing ones of bronze, 

 more susceptibility to injury thus, might be anticipated; but still very much 

 less than the amount to which the bronze field-guns of all the world (excepting 

 the few cast-iron field-guns said to be employed in Sweden, Denmark, and the 

 United States) are at present obnoxious. 



29. — The mutual relations of the Material of the Gun and of the rapidity of 



Explosion of the Charge. 



239. Since the year 1801, when Howard published his discovery of fulmi- 

 nating mercury (Pliil. Trans.), and his experiments, with Keir, upon its eflects 

 when substituted for gunpowder in fire-arms, it has been recognised, that some 

 explosive substances become gaseo\is with inconceivably greater rapidity than 

 others; that, in fact, the word explosive merely expresses a vague relation 

 between the volume of gas evolved from a solid or liquid, in changing its state 

 by chemical or molecular action, and the time occupied in that change ; so that 

 the coal that slowly becomes water and carbonic acid, &c., in our domestic fires, 

 and the gases suddenly liberated from an ignited charge of gunpowder, are but 

 extremes of a line of similar phenomena, connected in character, and differing 

 mainly in rapidity. 



240. Yet theexplosion of gunpowder itself, estimated byllutton as expanding 

 at a velocity of about 4700 feet per second, and found by Robins to be probably 

 about 7000 feet per second, is a comparatively slow combustion, and conversion 

 into gaseous matter, exceeded greatly in rapidity by many known agents, — 

 amongst some of the best known of which may be named, in the relative order 

 of rapidity of explosion : — 



