The frequent welding and re-rolling of iron is of the most beneficial tendency, the elongation of the fibres being highly advantageous; for, a fibrous piece of iron may be compared to a wire rope, the more strands the greater tenacity; and the smaller the strands, even up to a proximity of fineness to the human hair, the greater the weight they will bear in tension. One large wire which, when single, will suspend 500 lbs., will, when drawn down to six small ones, suspend 600 lbs.; and so on to the greatest extreme. Another great advantage received by the repeated reworking of iron, is obtaining an increased density; for when this is secured to a certain extent, you have closed in proportion the pores of the metal; and in this state it is not liable to that degree of expansion or contraction, or that fluctuation in strength, which arises from softening the iron. Nor can you gain, save to a limited extent, any improvement by hammering,--hammer-hardening, for instance,--simply because it is already improved to the utmost extent we are at present acquainted with.
How wonderfully beneficial to mankind is this beautiful arrangement of the metallic fibrous system! Without it what could we do? our manufactures would be confined to simple castings, or crystallizations, possessed merely of strength in proportion to the cohesive nature of the metal. Where would be all the wonderful springs whose fineness vies with the silken fibre? Of what could they be constructed? All-powerful gold would not suffice, nor silver; though each, in its place, possesses wonderful properties. Gold and silver may both be spread in the thinnest conceivable coat over space incredible; on the gilded cup, or, still thinner by electric agency, on the plated epergne. But iron alone is to the arts, the “_summum bonum_” for which there is no substitute: it is the “_sine quâ non_” of practical mechanics.
Improvements in the manufacture of a very superior iron may, we believe, be placed to the credit of the gunmaking profession exclusively; no other body or class of men having ever yet deemed it worth their trouble to endeavour to obtain anything of a better description _than bar iron, suitable to make steel from_. Mr. Mushet, from whose work I have already quoted, has evidently been more intimately acquainted with the routine of iron manufacturing than any other person I ever met with or read of: he understands the question perfectly; yet he seems to care for nothing further _than a suitable steel iron_.