involved in the Construction of Artillery. 167 



theory, by the instance that "a Swedish or Russian gun is never known to burst,'' 

 and that American and Swedish guns, even field-guns, are now fabricated of 

 some similar iron. 



The whole is a fallacy. There is no just reason to believe that any stronger 

 pig-iron is to be found from abroad than many well-known "makes" of Gi'eat 

 Britain. The fault is not in the iron, but in the want of skill to choose what sort 

 of iron to obtain from the blast furnace in the first instance, and how to recog- 

 nise and choose it for gun-founding, in the second. 



59. " Fine-grained gray mottled iron," it is constantly and truly said, is that 

 best fitted by tenacity and by elasticity for ordnance. But how is this in 

 England continually attempted to be obtained ? By mixing a perfectly white 

 lamellar No. 4 pig-iron, or " scrap metal," equally intensely hard and infusible, 

 with some soft, micaceous, or largely and coarsely graphitic dark gray, or almost 

 black No. 1 Scottish or Staffordshire pig-iron. The two, possessing totally dif- 

 ferent fusibilities, may be imperfectly mixed together, but they cannot be combined 

 by mixture. They form a mass of coarse mottled iron, with large black dots of 

 flat scales of graphite in a white ground, more or less like " hornblendic granite," 

 having a low density and small cohesion and elasticity. (Note H.) 



60. Let us observe what one of the ablest metallurgists of iron in Europe, 

 Karsten, a man well acquainted with Swedish iron industry, says as to the 

 modes by which the iron is chosen for those very Swedish guns : — " The tena- 

 city of gray cast-iron is much less in proportion as the metal has received a 

 more intense heat in the blast furnace, and if we require castings to give a very 

 great resistance we must not employ it ; that which is obtained from less 

 refractory ores, and in furnaces of loAver temperature, answers much better for 

 castings demanding much strength, provided that it be not too gray [too gra- 

 phitic], and that it do not expel too large a quantity of graphite [in cooling, 

 namely], which often gives rise to breaches of continuity in the interior. [Note I.] 

 In certain cases we must neither use one sort nor the other of iron [viz., neither 

 gray iron nor white, of which he before had spoken]. Cannon, for example, 

 must not be cast from gray cast-iron, especially when produced from a mix- 

 ture of refractory ores and flux, because then it contains always a large pro- 

 portion of earthy metals ; but even with readily fusible ores it is extremely 

 difficult so to work the smelting furnace that the pig-iron shall neither be too 

 gray nor too white, either of which is equally injurious for gun-founding. 



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