In a minute more, a gangway was hastily lowered from the wharf on to the deck; and the first man that came down it, pushed in front of a great crowd of eager, grinning, and elbowing negroes—mostly in search of small jobs among the passengers—was Bobby Whitaker. The moment he reached the deck, he seemed to take possession of it and of all the passengers by pure instinct, as if he were father to the whole shipload of them. The captain, the crew, and the other authorities were effaced instantly. Bobby Whitaker, with easy, greasy geniality, stood bowing and waving his hand on every side, in an access of universal graciousness towards the entire company. ‘My son!’ he said, looking round him inquiringly—‘my son, Dr Whitaker, of de Edinburgh University—where is he?—where is he? My dear boy! Let him come forward and embrace his fader!’
Dr Whitaker, in spite of his humiliation, had all a mulatto’s impulsive affectionateness. Ashamed and abashed as he was, he yet rushed forward with unaffected emotion to take his father’s outstretched hand. But old Bobby had no idea of getting over this important meeting in such a simple and undemonstrative manner; for him, it was a magnificent opportunity for theatrical display, on no account to be thrown away before the faces of so many distinguished European strangers. Holding his son for a second at arm’s length, in the centre of a little circle that quickly gathered around the oddly matched pair, he surveyed the young doctor with a piercing glance from head to foot, sticking his neck a little on one side with critical severity, and then, bursting into a broad grin of oily delight, he exclaimed, in a loud, stagey soliloquy: ‘My son, my son, my own dear son, Wilberforce Clarkson Whitaker! De inheritor of de tree names most intimately bound up wit de great revolution I have had de pride and de honour of effectin’ for unborn millions of my African bredderin’. My son, my son! We receive you wit transport! Welcome to Trinidad—welcome to Trinidad!’
SHOT-FIRING IN COAL-MINES:
AN IMPROVED METHOD.
Shot-firing or blasting in coal-mines is a subject which has for many years engaged the attention of mining experts and scientists, in consequence of the disastrous explosions which have so frequently resulted therefrom; but the discovering of an agent or the devising of a method by which the operation would be attended with perfect safety, has hitherto remained a problem too difficult to solve. At a very remote date in mining history, the use of explosives for blasting purposes was altogether unknown, and the various minerals, &c., were obtained from the bowels of the earth by means of hammer and wedge. Large quantities of these products were not then required, and the laborious and primitive method adopted for procuring them was fully equal to supplying the demand. But as time rolled on, mining produce became in much greater request, and means had to be devised which would enable mine-owners to meet the growing requirements of commerce and civilisation. Gunpowder was consequently utilised for this purpose, being first employed on the continent in 1620; and in the same year it was introduced into England as a blasting agent by some German miners brought over by Prince Rupert, and who employed it at the copper mine at Ecton in Staffordshire. Gradually it came into general use as a means of rapidly developing the mineral resources of the earth; and by its use, the output of our coal-mines has been increased by more than fifty per cent.
To its employment for obtaining coal, however, there were some great objections, both from a pecuniary and hygienic point of view. Large quantities of coal were converted into ‘slack,’ or a semi-pulverised state, in some cases to the extent of twenty-five per cent., and therefore great loss was sustained by the colliery proprietor, the marketable value of slack being very small. Again, the explosion of gunpowder is always attended with the formation of immense volumes of sulphuretted hydrogen, carbonic anhydride, and other gases, which are so deleterious to health, that, for a considerable space of time after a charge has been fired, the miners cannot work in that vicinity. Where large quantities of this substance are daily used, these noxious gases contaminate the air passing through the mine to such an extent that in the course of time they exercise an injurious effect on the health of the workmen.
Under these circumstances it was very desirable that other agents should be employed; but it is only within the last thirty years that other explosive substances have been submitted to mine-owners. The first of these was gun-cotton, which was invented by Professor Schönbein in 1846. It was not, however, until some years after its discovery that it came into use as a mining agent, such serious explosions attending its manufacture and storing, immediately after its introduction to the world, that no one would have more to do with so deadly an explosive. Eventually, however, it was ascertained how to render it safer, and it came into extensive use as a mining agent. Though it burns harmlessly away when simply ignited, yet, when fired by means of a detonator, as is done for mining purposes, it possesses some six times the explosive power of gunpowder; and its combustion in this way is so complete that no noxious gases are given off. It can be used either in the form of yarn or in a compressed block. When used in the former state, it is the opinion of many that its combustion is too rapid, and that it is thereby prevented doing its full amount of effective work. It bursts the minerals asunder with great force; but it lacks the cutting property which is essential to the performance of good work. The compressed cotton is free from these defects. It possesses all the force of yarn cotton; and in consequence of its slower combustion, it cuts in such a way as to make the block of mineral ready for the next charge. This latter is a great advantage to the workman, and hence the gun-cotton used for mining purposes is generally in a compressed state. By the use of this agent, mining of all descriptions was immensely facilitated, and the dangerous operation of ‘tamping,’ or filling the shot-hole with brick or coal dust rammed hard, was rendered unnecessary.
At a somewhat later period, nitro-glycerine attracted much attention, the first to attempt its use as an explosive agent being Alfred Nobel, a Swedish engineer, in 1864. So far as explosive power was concerned, it was all that could be desired, possessing ten times the force of gunpowder, and therefore being of nearly double the strength of gun-cotton. On the other hand, it was open to most serious objections. The danger of its exploding from concussion was very great, and many dreadful accidents have thus been caused by it. The liquid also, when poured into a shot-hole, has frequently run into some unknown crevice, and when fired, has produced an explosion under the very feet of the miners. To obviate this in some degree, cartridges have been employed; but in whatever light it is viewed, nitro-glycerine is a most perilous explosive.
To remove many of the dangers associated with the use of nitro-glycerine, particularly those of concussion, Mr Nobel invented dynamite, which was tried and approved as a mining agent at Merstham in 1868. When properly prepared, it constitutes one of the safest, most convenient, and most powerful explosives applicable to industrial purposes. It burns without explosion when placed in a fire or brought into contact with a lighted match. If struck with a hammer on an anvil, the portion struck takes fire without igniting the dynamite around it; and if packed with moderate care, it may be transported by road, railway, or canal with little danger of an explosion either from heat, sparks, friction, concussion, or collision. Such conditions of safety, however, entirely depend upon dynamite being properly made. If the Kieselguhr or porous infusorial earth, of which it contains about twenty-five per cent., be not properly dried and prepared, so as not only to absorb but to permanently hold in absorption the nitro-glycerine mixed with it, exudation is apt to take place; and if this only occurs to the extent of a thin greasy layer over the surface, there are present all the dangers of nitro-glycerine pure and simple. It is of a pasty consistence, and thus possesses the advantage that, whilst being very little less powerful as an explosive than nitro-glycerine, bore-holes can be filled with it without the dangers attending that liquid, and no cartridge case is required.
Since the introduction of dynamite, several other nitro-compounds have been brought forward as blasting agents, such, for instance, as dualine, lithofracteur, blasting gelatine, and gelatine-dynamite. With the exception of the two last named, however, they have not found much favour as mining agents in this country, and their use is mainly confined to the continent.
Whilst all the explosives mentioned in this article are more or less suited to blasting in mines, so far as their propulsive force is concerned, yet the use of each and all is attended with great danger in a coal-mine, and for the following reason: coal, being of vegetable or organic origin, is constantly giving off numerous gases, the most dangerous of which, under ordinary circumstances, is methylic hydride or marsh-gas, known in mining districts as fire-damp. It is of an inflammable nature; and when it becomes mixed with from seven to ten times its volume of air, it is highly explosive. It was the presence of this gas in coal-mines that gave rise to the researches of Humphry Davy and George Stephenson, and which resulted in the production of two kinds of safety-lamp, differing but little from each other in construction. As a mark of distinction for his invention, the first-named gentleman received the honour of knighthood. Explosive as is methylic hydride when mixed with air in the proportions stated, it becomes infinitely more so when the air contains a proportion of coal-dust. A very small percentage of fire-damp when mixed with air and coal-dust is sufficient to cause a disastrous explosion. In all dry coal-mines there is a considerable quantity of coal-dust (coal in a state of impalpable powder) lying about, and a certain proportion of it is always floating in the air through the workings of the mine. Now, when explosives are used, no matter how they are ignited, their combustion is always attended with the formation of a mass of flame, and consequently there is always great danger of an explosion of fire-damp taking place. Especially is this the case with gunpowder, which, requiring to be used in large quantities to produce the desired effect, is accompanied with much flame at the moment of its ignition. Gun-cotton being a much more powerful explosive than powder, can be used in far smaller proportions, and therefore to a certain extent possesses an advantage over it, inasmuch as its combustion is not attended with so great a mass of flame; thus to some extent, though only very slightly, reducing the danger of an explosion of fire-damp. In addition to showing flame at the moment of its ignition, dynamite possesses the drawback, that the Kieselguhr is liable to become incandescent, and whilst in this state, to be blown about by the force of the explosion of the blasting charge, and so fire any gas or mixture of gas and coal-dust which may be in the vicinity.