[10] The London makers are again using them extensively; which is certainly no proof of their judgment.
The use of old horse-shoe nails is of a date nearly coeval with the use of small fire-arms. These nails are made from rod iron of the best description; and the hammering cold, or tempering the nail, so benefits and condenses the iron as to improve it greatly. The method in use until a late period, was to fill and force into an iron hoop, of six or seven inches diameter, as many stubs as it would contain, to weld the whole, and draw them down to a bar of such dimensions as might be required. Modern improvement, however, has shown the advantage of cleansing the stubs perfectly by a revolving drum, and then fusing and gathering them into a bloom on the bed of an air-furnace. Thus a body of from 40 to 50 lbs. of melting iron can be obtained at one heat; a matter of economy and necessity, where large quantities are required, besides possessing the superior advantage of having the whole mass equally heated: this cannot be done by the old hoop method, as the surface must be frequently burnt before the interior is at all in a welding state.
Experience taught the late Mr. Adams and his brother George—who still manufacture some of the best gun iron in the world—that the stub iron alone was insufficient; for even then (forty years ago) the absurdity of imagining that no barrels were or could be good without being soft, was understood and acted upon by them. They introduced at first one-fourth of steel to three of stubs; this having been found highly advantageous, the prejudices of the gun-makers were gradually overcome, or left in abeyance from ignorance of the introduction. It is a fact, that as late as 1842, when I issued my former work, men who had been all their lives gun-makers (by courtesy) actually refused to believe that any steel at all entered into the composition of the best barrels; and several whom I know perfectly well, ordered the factors with whom they dealt “to be sure to send them no barrels with steel in, as they did not wish their customers’ hands to be blown off.”
Charcoal iron has, up to this day, been the only stub twist barrels they (and we believe two-thirds of the provincial makers also) have ever been served with. Reason with these men, and they will snappishly tell you, “We pay the best price, and we ought to have the best: we don’t see that our neighbours have any better.” On one occasion of my calling upon one of the first provincial gun-makers in the kingdom, the subject of barrels was adverted to—“An excellent work that of yours, I dare say; but, sir, you have done a deal of harm: it is wrong to let gentlemen know too much; they give you far too much trouble: they get too knowing.” These, and such like observations, are the only thanks I ever received from the generality of the gun trade. There are, however, some enlightened men who, understanding the subject, have appreciated my motives; but by far the greater proportion have done the reverse, asserting “that I had told them nothing but what they knew before.”
The mixture of a portion of steel with the stubs having clearly shown an improvement, an increased proportion has been adopted by various makers: we have had as high as three-fourths of steel to one of iron. Where proper attention is paid to the clipping of the steel to pieces, corresponding with the stubs, and properly mixing the whole, welding and forging by the heavy hammer, reducing by a tilt and rolling down to the smallest description of rod, a most excellent, tenacious, and dense body of iron is thus obtained; while, by cutting into lengths of six inches, bundling a number together, and re-welding them into a bar, an increased density and tenacity is gained, by an increase in quantity, and an elongation of the fibrous system. Any description of barrel, of this iron, if made with a moderate degree of care and attention, is considerably stronger than any explosive fluid ever yet compounded could burst, under any circumstances bordering on fair experiment.
The great advantage derived from welding on the bed of an air-furnace, arises from an absence of the minute portions of charcoal, of either wood or coal, as the case may be. Millions of these very minute portions are imbedded in the midst of the metal in every part. They are enclosed in cells originally of their own dimensions, but are drawn out with the fibres to an indefinite extent, forming a system of tubes that may be compared to the capillary system in trees, and making the iron of a spungy, compressible nature. It is the absence of these particles of charcoal that gives part of the superiority to steel as now made for gun-barrels; and the existence of a portion of them causes the inferiority of all other kinds of iron. In a chemical analysis of iron, a large portion of crude coal-charcoal or wood-charcoal is found, according as either has been used during the manufacture. This is not of course given as so much carbon in the result, though the injury is equally detrimental as an excess of carbon is to the goodness of the metal; for it renders the whole porous, and liable to attract moisture and induce oxidation. It must be kept prominently in view, and clearly comprehended, that the denser the body of metal, the less the liability to oxidise, or in other words rust; and here is the one great preservative principle in good iron: “it is the fibre of dense cocoa-wood, compared with that of willow or saugh.” In all situations and for all purposes, where iron is liable to sudden changes of either heat or cold, wet or dry, the very best of iron should be obtained; as it will be less affected by the changes of temperature, and amply repay by its durability the extra cost in the first instance.
The very extensive round of experiments to which I have submitted mixtures of this nature, clearly establishes all the conclusions I have formed on these points. The strength of the mixture, three parts steel to one of stubs, gives a resistance in the rod of 6-16ths broad by 5-16ths thick, and 12 inches long, containing 1·40625 solid inches, equal to 10,295 lbs. before separating; thus being equal, in a barrel of the dimensions before mentioned, to an internal pressure of 5,555 lbs. to the inch of tube. The proportions mentioned in my previous work are 25 lbs. of stubs to 15 lbs. of steel; the strength of this mixture in the rod is equal to a tension of 8,960 lbs., and the barrel is capable of restraining a pressure internally of 4,818 lbs., making full 15 per cent. dissimilarity in favour of the larger proportion of steel: indeed, all experience points to the great advantage, that steel, properly worked, possesses over iron alone. Great good can be effected by condensing iron by hammer-hardening; greater than I have shown steel to be capable of receiving additionally: as, already having it naturally, there is no necessity for using artificial means to obtain it. Nor is steel so liable to depreciation in the hands of an inexperienced artisan; as the degree of expansion is not more, in the large proportion of steel mixture, than a loss of strength equal to 41⁄2 per cent, by heating and cooling gradually. The loss in the mixture containing less steel is 71⁄2 per cent. The specific gravity of the two is in proportion.
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.