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BOOK V.
119
out because of the hardness or other difficulty, and the drift or tunnel is
low, a heap of dried logs is placed against the rock and fired ; if the drift or tunnel is high, two heaps are necessary, of which one is placed above the other, and both burn until the fire has consumed them. This force does not generally soften a large portion of the vein, but only some of the surface. When the rock in the hanging or footwall can be worked by the iron tools and the vein is so hard that it is not tractable to the same tools, then the walls are hollowed out ; if this be in the end of the drift or tunnel or above or below, the vein is then broken by fire, but not by the same method ; for if the hollow is wide, as many logs are piled into it as possible, but if narrow, only a few. By the one method the greater fire separates the vein more completely from the footwall or sometimes from the hangingwall, and by the other, the smaller fire breaks away less of the vein from the rock, because in that case the fire is confined and kept in check by portions of the rock which surround the wood held in such a narrow excavation. Further, if the excavation is low, only one pile of logs is placed in it, if high, there are two, one placed above the other, by which plan the lower bundle being kindled sets alight the upper one ; and the fire being driven by the draught into the vein, separates it from the rock which, however hard it may be, often becomes so softened as to be the most easily breakable of all. Applying this principle, Hannibal, the Carthaginian General, imitating the Spanish miners, " they frequently use bruising machines, carrying 150 librae of iron." This combination
of fire and vinegar he again refers to (xxiii, 27), where he dilates in the same sentence on the usefulness of vinegar for breaking rock and for salad dressing. This myth about breaking rocks with fire and vinegar is of more than usual interest, and its origin seems to be in the legend that Hannibal thus broke through the Alps. Livy (59 B.c., 17 a.D.) seems to be the first to produce this myth in writing ; and, in any event, by Pliny's time (23-79 A.D.·) it had become an established method—in literature. Livy (xxi, 37) says, in connection with Hannibal's crossing of the Alps : " They set fire to it (the timber) when a wind had arisen suitable to " excite the fire, then when the rock was hot it was crumbled by pouring on vinegar (infuso " aceto). In this manner the cliff heated by the fire was broken by iron tools, and the " declivities eased by turnings, so that not only the beasts of burden but also the elephants " could be led down." Hannibal crossed the Alps in 218 B.c. and Livy's account was written 200 years later, by which time Hannibal's memory among the Romans was generally surrounded by Herculean fables. Be this as it may, by Pliny's time the vinegar was generally accepted, and has been ceaselessly debated ever since. Nor has the myth ceased to grow, despite the remarks of Gibbon, Lavalette, and others. A recent historian (Hennebert, Histoire d' Annibal n, p. 253) of that famous engineer and soldier, soberly sets out to prove that inasmuch as literal acceptance of ordinary vinegar is impossible, the Phoenecians must have possessed some mysterious high explosive. A still more recent biographer swallows this argument in toto. (Morris, " Hannibal," London, 1903, p. 103). A study of the commentators of this passage, although it would fill a volume with sterile words, would disclose one generalization : That the real scholars have passed over the passage with the comment that it is either a corruption or an old woman's tale, but that hosts of soldiers who set about the biography of famous generals and campaigns, almost to a man take the passage seriously, and seriously explain it by way of the rock being limestone, or snow, or by the use of explosives, or other foolishness. It has been proposed, although there are grammatical objections, that the text is slightly corrupt and read infosso acuto, instead of infuso aceto, in which case all becomes easy from a mining point of view. If so, however, it must be assumed that the corruption occurred during the 20 years between Livy and Pliny. By the use of fire-setting in recent times at Königsberg (Arthur L. Collins,
" Fire-setting," Federated Inst, of Mining Engineers, Vol. V, p. 82) an advance of from 5 to 20 feet per month in headings was accomplished, and on the score of economy survived the use of gunpowder, but has now been abandoned in favour of dynamite. We may mention that the use of gunpowder for blasting was first introduced at Schemnitz by Caspar Weindle, in 1627, but apparently was not introduced into English mines for nearly 75 years afterward, as the late 17th century English writers continue to describe fire-setting. |
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