The proportionate number of bands cut from the three sizes of cups were, as a general rule, three from the smallest or 4·5-inch, eight from the intermediate or 6-inch, and one only from the largest or 8-inch, and it was in some measure due to these circumstances, due, no doubt, too, to a certain difficulty in obtaining delivery of copper sheets in sufficient quantities, that for the purpose of increasing the output of 8-inch bands and of maintaining this output on a level with that of the two smaller sizes, recourse was had to the brass foundry, where it was considered practicable to cast the bands, especially in view of the amount of copper scrap of both shearings and turnings that was available for melting-down purposes.
A certain amount of preliminary experimental work was perforce entailed, both for ensuring that the band, when cast, should exhibit an estimated degree of shrinkage (for the greater the shrinkage the sounder the casting, a shrinkage of 1/4 inch being usually accepted as a minimum), and that the metal should be capable of withstanding certain specified Government tests, the one condition, of course, being contingent on the other. Tests which were actually made proved wholly satisfactory, the average results being an elastic limit of 7·5 tons per square inch, an elongation of 45 per cent. on two inches, and finally a breaking stress of 14·5 tons.
De-oxidisation, that is to say the process of removing oxygen from the metal for the purpose of obtaining castings that were sound, free of blow-holes and of oxide of copper, was effected by mixing a small percentage of phosphor-copper with the molten copper in the crucible.
Boron-copper was also tried as a de-oxidiser, but no real advantage was noticeable. Comparative tests, too, were made for the purpose of ascertaining the percentage of loss of copper when melted in crucibles and again in a reverberatory furnace. The former process resulted in a loss not exceeding 3/4 or 75 per cent.; whereas the latter was responsible for a 7 per cent. loss. Any saving which came within the meaning of the word "economy" as completely removed and distinct from that of "parsimony" was a precept not merely preached but extensively practised throughout the locomotive department at Crewe, and as an illustrative instance of this praiseworthy, and therefore patriotic, policy the casting of copper bands may be cited.
Although cheaper and possibly less reliable methods of producing copper bands may have conceivably come into being during the final stages of the war, it was obvious to even the least well-informed in such matters that, provided a mixture could be obtained whereby the metal could be relied upon to pass the Government tests, the process of pouring molten copper from a crucible into a sand-cored cast-iron chill was likely to be at any rate cheaper than that involving the employment of presses, rolls, shears, and punches.
On comparing the estimated cost of manufacturing copper bands by the pressing and casting processes respectively, a difference of one shilling per finished band was shown in favour of the latter system; and although it may seem a mere bagatelle, a drop in the ocean of squandered millions, to those who not merely are encouraged, but who encourage others, in the art of reckless and profligate extravagance when handling the public purse, this modest shilling per copper band saved represented an aggregate of £1750, a sum not altogether to be sneezed at when we consider that the value of the 35,000 bands cast in Crewe Works was but an infinitesimal fraction of the total munition expenditure during the war.
We are told that "the use of travelling is to regulate imagination by reality, and instead of thinking how things may be, to see them as they are." Hence it has been, we may confidently aver, for the purpose of seeing things as they are that we have availed ourselves of this opportunity to fathom in some measure for ourselves the abstruse art of shell-manufacture as practised in Crewe Works. The imagination, however morbid and obtuse, can hardly fail to be stirred when pondering the rotund and rudimentary profile of the rough shell-forging lying with all its latent possibilities, recumbent in the lathe; ultimately in its finished form c'est cela,[6] the shell we meditate, qui va nous débarrasser des Prussiens; thanks now to that generous impulse which prompts our gallant gunner-men, good fellows all, possessed of "mildest manners with the bravest mind," to unravel for us the all-absorbing mysteries of that sphere of "war's glorious art" in which they themselves excel, reality will regulate our questioning imagination as we follow them to the dim seclusion of some cleverly camouflaged gun-emplacement.
We have already seen that the motion of a shell is rotary as well as forward, this rotary motion being brought about by the joint instrumentality of the grooving of the bore of the gun and of the copper band on the shell.
Another and very important function performed by the copper band approximates to that of the piston-ring of a locomotive cylinder, which prevents the passage of steam from one side of the piston to the other. Concomitantly, the copper band, turned a fit in the bore of the gun and jammed into the rifling, is designed to obstruct the passage of the propellent gases beyond the base-end of the shell; these gases are naturally imbued with a habit or hobby of gnawing away, or eroding, any metal surfaces with which they can come into contact, so that the further they can penetrate up the bore of the gun, the more material damage that will ensue, and the rifling becomes proportionately erased or eaten away. Further, owing to the fact that the degree of heat generated by the ignition of the propellent charge is obviously most intense in the area most adjacent to the base of the shell, erosion becomes patently more pronounced here than in other directions; consequently as the area in which the propellant gases are exploded increases, so the pressure exerted by these gases decreases, the net results of these considerations being loss of accuracy and of velocity.
Different civilised communities favour different kinds of explosives as a gentle means of attaining their ambitions, and these explosives may be solids, liquids, or gases. In this country picric acid (or, tri-nitro-phenol), and tri-nitro-toluene (or in its abbreviated and more easily pronounced form "T.N.T.") are the two kinds most extensively adopted for the filling of high-explosive shells. Owing, however, to certain unexplained caprices in which it is known to indulge, owing, too, to the fact that persons employed on its manipulation have died from the effects of trotyl poisoning, T.N.T. is less extensively employed, in spite of certain known and obvious advantages which it possesses over picric acid.