Discoveries and Inventions of the Nineteenth Century

For example, the substances employed for propelling projectiles from guns must not have the violent rending power of certain others, which, by this very property, are most useful for blasting operations; and, again, although explosives of this last kind are inadmissible as projectile agents, they are of the kind best adapted for use in shells where it is the disruptive action that is required. Also in blasting operations, the explosive has to be adapted to the nature of the work, and it has been found that a substance which has worked well in driving a heading for a tunnel through one kind of rock may prove both slow in progress, and more costly in expenditure, when some different kind of rock is reached. Besides this, regard must be had in blasting operations to the nature of the effect required, which is in some instances a shattering of the rock into fragments, in others a detachment of it in masses. Thus, in the working of a slate quarry, the explosive used must not be of a nature to shiver the rock into useless splinters, but must operate in such a manner that compact masses may be separated from the mountain side in a condition suitable for cleaving, by appropriate tools, into numberless broad laminæ, which, trimmed 749into rectangular shape, constitute our well-known roofing slates. The blasting used on a coal seam must be so conducted as to yield the material as much as possible in big lumps or cobbles rather than in slack. When granite is blasted for the purpose of obtaining building stones, the explosive must be one that, by its comparatively slow action, divides the compact rock into the largest possible blocks. On the other hand, when granite is blasted merely with the object of removing it, as when a tunnel has to be driven through a mass of it, the most disintegrating agent is then the best. The common popular expressions by which the two classes of explosives just referred to are distinguished are “high explosives” and “low explosives.” Dynamite may be taken as a type of the former, and gunpowder a type of the latter. As will be gathered from what is to follow, no definite separation between these classes can be fixed, but in a general way it may be said that, where a destructive, rather than a propelling or pressure effect is required, the explosive used is one brought into operation by a concussive or detonating priming, and acting mostly by detonation within itself, such as dynamite, &c. Whereas, up to nearly the middle of the nineteenth century, gunpowder was practically the only explosive in use for either civil or military purposes, the close of the century can show a list of several hundred preparations that have been proposed or actually used in its stead. The names by which these are put forward are expressive sometimes of an ingredient in their composition, such as “ammonia dynamite,” “cellulosa,” “mica powder,” “dynamite au carbon,” “dynamite de boghead,” &c.; and sometimes the inventor’s name, as “So-and-so’s powder or explosive”; sometimes of the strength of the mixture under various fanciful names, such as “dynamite,” “heraklin,” “vigorite,” &c., &c.; sometimes the names relate to the appearance of the compound, as “white gunpowder,” “blasting gelatine,” &c., &c.; and sometimes to other circumstances, such as “pudrolithe,” “saxifragine,” “safety powder,” &c., &c. A very long list might be given of the substances severally used in these various compositions. It will be sufficient to indicate the general nature of the several classes into which the new explosives may be divided. By turning back to p. 746, the reader will be reminded of the composition of gunpowder, and of the part played therein by the nitre (nitrate of potassium). Now a considerable number of the recently patented explosives are simply modified gunpowders, which all contain some nitrate, replacing wholly, or in part, the nitrate of potassium, while sulphur is an ingredient of nearly all, and in many, the charcoal of gunpowder is partly or wholly replaced by other carbonaceous materials, such as sawdust, coal-dust, tan, starch, paraffin, lycopodium, graphite, peat, flour, bran, &c. Certain mineral salts enter into the composition of some, such as sulphate of iron, carbonate of copper, sulphide of antimony, &c., &c. In another class of the newer explosives chlorate of potassium takes the place of the nitrate as the oxygen supplying material, with similar variations as to the carbonaceous matter as are referred to above. Yellow prussiate of potash and sugar sometimes replace both the charcoal and sulphur of gunpowder in this class. Explosives of this chlorate class are usually dangerous to manufacture, and are often very sensitive, and also liable to changes by keeping, which render them still more dangerous. 750The next class of preparations brings us to the “high explosives,” properly so called, and it is among these that most notable preparations are met with. Of all the explosive nitro-compounds, gun-cotton was the first practically employed (vide p. 741); but very soon after nitro-glycerine was discovered by Sobrero when working in Pelouze’s laboratory. This afterwards became known as “blasting oil,” but it was many years before nitro-glycerine came into use as an explosive, namely, when, about 1860, Nobel, a Swedish engineer, had established factories for its production as an agent for blasting. At first there were difficulties and dangers attending its use, and it was only when Nobel had discovered the detonation method of setting free its tremendous energy that the new era of “high explosives” really commenced. Between 1860 and 1870 such a number of appalling catastrophes occurred in the handling of the new “blasting oil” that in several European countries its use was entirely prohibited. And, in England at least, this prohibition remains, for “in a liquid state this explosive cannot be sold in, or imported into this country. It is manufactured under the strict provision that it is forthwith made up into dynamite or some kindred licensed explosive.” ... “The only source, practically speaking, of nitro-glycerine on a commercial scale in this country is the factory of Nobel’s Explosive Co. (Ltd.) at Ardeer, in the county of Ayr.”[17] Nitro-glycerine being so extremely dangerous to handle in the liquid form led Nobel to propose its use in an altered condition, by causing it to be absorbed by some inert porous material, the most suitable being a siliceous earth found in Germany, and there known as kieselguhr, of which one part will absorb three times its weight of liquid nitro-glycerine. Here we have the original dynamite, but now other substances are used for absorbing the liquid, and there are, indeed, dynamites of two different classes: 1. Dynamites with inert absorbents. 2. Dynamites with absorbents which are themselves combustible, or explosive. 17. Major Cundill, H.M.’s Inspector of Explosives. Of the latter class there are endless varieties. One that has latterly been much used is called “blasting gelatine,” and is practically a combination of nitro-glycerine and nitro-cotton, this last ingredient being a less nitrated cellulose than gun-cotton. Blasting gelatine contains a very large percentage of nitro-glycerine (93–95 per cent.), and has the appearance of stiff jelly of a pale yellow colour. It may be of interest to remark that this second class of dynamites admits of well-defined sub-divisions according to the nature of the absorbent, as: (a) Charcoal, or other simple carbonaceous material. (b) Gunpowder, or other nitrate or chlorate mixtures. (c) Gun-cotton, or other nitro-compounds. 751 Fig. 340.—View on the Tyne. MINERAL COMBUSTIBLES. Certain mineral combustibles may fairly claim attention in a work treating of the discoveries of the nineteenth century, not because these bodies have been known and used only in recent times, but for other reasons. The true nature of coal—that most important of all combustibles—its relation to the past history of the earth, and to the present and future interests of mankind; the work it will do; the extent of the supply still existing in the bowels of the earth; the innumerable chemical products which it yields—are subjects on which the knowledge gained during the present century forms a body of discovery of the most interesting and important kind. Another substance we have to mention, though not a modern discovery, has lately been found in far greater abundance, and is now so largely used for various purposes, that it has become an important article of commerce. COAL. Fig. 341.—Fossil Trees in a Railway Cutting. Most persons know, or at least have been told, that coal is fossil vegetable matter,—the long-buried remains of ancient forests. But 752probably many receive the statement, not perhaps with incredulity, but with a certain vague notion that it is, after all, merely a daring surmise. And, indeed, nothing is at first sight more unlike stems, or leaves, or roots of plants than a lump of coal. Then everybody knows that coal is found thousands of feet beneath the surface of the earth, whereas plants can grow only in the light of the sun. One begins to understand the matter only when the teachings of geology have shown him that, so far from the crust of the earth being, as he is apt to suppose, fixed and unchangeable, it is in a state of constant fluctuation. Changes in the levels of the ground are always going on: in one place it is rising, in another sinking; here a tract of land is emerging from the ocean, there a continent is subsiding beneath the water. The extreme slowness with which these changes proceed causes them to escape all ordinary observation. The case may be compared to the hour-hand on the dial, which a casual spectator might pronounce quite stationary, since the observation of a few seconds fails to detect its movement. As the whole period comprehended in human annals counts but as a second of geological time, it cannot be wondered at that it required a vast accumulation of facts, and much careful and patient deduction from them, before a conclusion was reached so apparently contradictory of experience. It is, indeed, startling to learn that “the sure and firm-set earth” is in a state of flow and change. Even the “everlasting hills” give evidence that their materials were collected at the bottom 753of the sea, and we know that the water which runs down their sides is slowly but surely carrying them back particle by particle. Of the magnitude of the changes which the surface of the earth has undergone in times past, and which are still imperceptibly but constantly proceeding, the ordinary experience of mankind can of itself give no example. But such changes have sufficed to entomb a vast quantity of relics of the innumerable forms of vegetation which flourished and waved their branches in the sun, ages upon ages before the advent of man. Fig. 342.—Impression of Leaf found in Coal Measures (Pecopteris). It may be thought impossible that vegetable matter should have so changed as to become a dense, black, glistening, brittle mass, showing no obvious forms of leaves or texture of wood. But no one who has seen how a quantity of damp hay closely pressed together will, after a time, become heated and change in colour to black, can have any difficulty in comprehending how chemical and mechanical actions may completely alter the aspect of vegetable matter. We have, however, the most direct evidence of the vegetable origin of coal in the numberless unquestionable forms of trees and plants met with in all coal strata. Sometimes the trunks of the trees fossilized into stony matter are found upright in the very situation in which they grew. Thus in Fig. 341 is represented the appearance exhibited by the trunks and roots of some fossil trees, which were exposed to view in the formation of a railway cutting between Manchester and Bolton. In every coal-field also beautiful impressions of the stems and leaves of plants are met with—one common form of which is shown in Fig. 342. Most of the plants so found belong to the flowerless division of the vegetable kingdom. Some are closely allied to the ferns of