230 ARTILLERY 



the ancestors of all modern breech-loading guns ; and culverins, which replaced the 

 iron serpentines, and wore of enormous length, 35 to 60 calibres, and great strength 

 towards the breech, but of small calibre. Many examples remain of a later date : one 

 at Dover Castle, another in the Dial Square, Woolwich Arsenal, and the celebrated 

 one of Nancy (1598), above 21 feet in length, carrying about an 18-pound iron ball. 

 In England the earliest bronze guns are said to havo been cast by one John Owen, 

 in 1535. 



Few examples are met with of guns formed of metal in strictly atomic propor- 

 tions ; but alloys are found therein presenting every formula, from 7Cu + Snupto 

 83Cu + 4Sn. The proportions most approved of in the arsenals of Europe appear to 

 vibrate between 100 by weight of copper to 9 of tin, up to 100 of copper and 12 of 

 tin. In France, 100 copper +11 tin by weight is the proportion fixed by law, and 

 invariably aimed at. In the United States, 100 copper + 12*5 tin is adopted for certain 

 species of guns. 



The proportions of tin and copper used in making bronze guns in the United 

 States : Density Tenacity 



Tin, 1 part . . 7'297 . . 2,122 



Copper, 8 parts 

 Mean proportional . 

 Mean of 83 guns 



8-672 . . 24,252 



8-519 . . 21,793 



8751 



8-523 . . 29,655 



Mean of 83 gun-heads 



Bronze guns are liable to drop at the muzzle ; this is clue to the unequal tempera- 

 ture of the inside and of the outside of the gun. 



Brass ordnance are made of what is called GTJN-METAL, composed of about 10 parts 

 of copper and 1 of tin. 



One of the first inquiries of importance in connection with the construction of 

 pieces of artillery is that of the liability to fracture in the metal. Upon this point 

 the researches of Mr. Mallet furnish much important matter. He tells us, as the 

 result of his investigation, that it is a law of the molecular aggregation of crystalline 

 solids, that when their particles consolidate under the influence of heat in motion, their 

 crystals arrange and group themselves with their principal axes in lines perpendicular to 

 the cooling or heating surfaces of the solid : that is, in the lines of the direction of the 

 heat-wave in motion, which is the direction of least pressure within the mass. And this 

 is true, whether in the case of heat passing from a previously fused solid in the act of 

 cooling and crystallising in consolidation, or of a solid not having a crystalline 

 structure, but capable of assuming one upon its temperature being sufficiently raised, 

 by heat applied to its external surfaces, and so passing into it. 



Cast-iron is one of those crystallising bodies which, in consolidating, obeys, more 

 or less perfectly according to conditions, the above law. In castings of iron the 

 planes of crystallisation group themselves perpendicularly to the surfaces of external con- 

 tour. Mr. Mallet, after examining the experiments of Mr. Fairbairn who states 

 ('Trans. Brit. Ass.' 1853) that the grain of the metal and the physical qualities 

 of the casting improve by some function of the number of meltings ; and he fixes on 

 the thirteenth melting as that of greatest strength shows that the size of crystals, 

 or coarseness of grain in castings of iron, depends, for any given ' make ' of iron 

 and given mass of casting, upon the high temperature of the fluid iron above that just 

 necessary to its fusion, which influences the time that the molten mass takes to cool down 

 and assume again the solid state. 



The very lowest temperature at which iron remains liquid enough fully to fill 

 every cavity of the mould without risk of defect, is that at which a large casting, 

 such as a heavy gun, ought to bo ' poured.' Since the cooling of any mass depends 

 upon the thickness of the casting, it is important that sudden changes of form or of 

 dimensions in the parts of cast-iron guns should bo avoided. In the sea and land 

 service 13-inch mortars, where, at the chamber, the thickness of metal suddenly 

 approaches twice that of the chase, there is evidently a malconstruction. 



The following statements of experiments made to determine the effect produced on 

 the quality of the iron in guns, by slow or rapid cooling of the casting, are from the 

 report of Major W. Wade, of the South Boston Foundry, to Colonel George Bomford, 

 of the Ordnance Department of the United States. Three six-pounder cannon were 

 cast at the same time from the same melting of iron. The moulds were similar and 

 prepared in the usual manner. That in which No. 1 was cast was heated before 

 casting, and kept heated afterwards by a fire which surrounded it, so that the flask 

 and mould were nearly red hot at the time of casting ; and it was kept up for three 

 days. Nos. 2 and 3 were cast and cooled in the usual way. 



At the end of the fourth day the gun No. 1 and flask were withdrawn from the 

 heating cylinder while all parts were yet hot. Nos. 1 and 2 were bored for 6- 

 poundors in the usual way; No. 3 for a 12-pounder howitzer, with a 6-pounder 



