involved in the Construction of Artillery. 239 



ment had at length purchased the invention for 36,000 thalers. No more has 

 been heard in this country of the method, which has, therefore, probably not 

 turned out as valuable as at first supposed. Were it not that the adaptation of 

 wrought-iron to artillery forms our present horizon of improvement, rather than 

 the improved use of bronze, it would seem a research worthy of careful expe- 

 riment upon the large scale, how far this process might be advantageous. The 

 means of thus precipitating together, in determinate proportions, two or more 

 different metals, and the fact that when precipitated they form true alloys, has 

 been known several years, and the conditions investigated by Becquerel and 

 others. That metals so aggregated in some instances possess great solidity and 

 density is certain, it being long well known to copperplate engravers, that the 

 copper precipitated locally upon a rolled plate for engraving, is much harder 

 and denser than the other parts of the plate, which were obtained by fusion, 

 lamination, &c. Metals thus precipitated are, however, always aggregated in 

 crystals, which, in accordance with the general law, will have their principal 

 axes in the direction of least pressure while forming, which will probably be 

 in directions transverse to the electric current. The molecular arrangement of 

 the mass will, therefore, be very uniform and simple, and probably very ana- 

 logous to that of cast-iron in cast objects ; but the mutual coherence of the 

 crystals, in the absence of all mechanical pressure upon the mass, may yet be 

 very slight ; homogeneity of composition, however, would be almost certainly 

 attained. 



183. Amongst the many projects for improved guns recently brought for- 

 ward, there has been more than one for lining the interior of cast or of wroughtr 

 iron guns with gun-metal, — in fact, making a bronze gun, strengthened with iron 

 externally. The idea is a very old one (see Note A), but practically valueless. No 

 rigid combination of gun-metal and iron can be adopted with permanent success 

 for artillery, from the great disparity of expansibility by heat, and of extensi- 

 bility by equal strain, between the two metals, — the amount and some effects of 

 which have been already discussed, and which in this case is sufficient to tear 

 asunder ere long any connexion attempted between the metals. 



184. In the comparative experiments made at Lafere with cast-iron guns 

 made in Sweden, Scotland, and France, in 1836, there was good ground for 

 believing that an appreciable weakening occurred, of the guns into which copper 



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