but, nevertheless, either of them is possible in some cases, and would answer the purpose of draining a goaf, where desired, and at little

expense.

But in these attempts to drain the goaves of the gas collected in them, are we doing all that is needed? Every miner will answer, "No!' Dangerous though these receptacles of noxious matter may be, we have them under control to a very great extent. We know where each is situated, we are aware that they are charged with gas, and we take precautions accordingly.

Accumulations also of gas may be formed in at least two other ways. Suppose, first, that the ventilating current of air is not strong enough to dilute and carry away the gas which exudes from the pores of the coal forming the front and sides of a drift when newly excavated. This gas will soon form an explosive mixture with the air, and lie in some corner of the drift ready to take advantage of a defect in a safety-lamp or of any carelessness on the part of master or workman.

Again, outbursts of gas, or 'blowers,' as I would prefer to call them, whether they issue from the stone roof and floor or from the coal itself, but originating of course primarily in the coal, must be taken into account. These are very dangerous, as their occurrence is sudden and generally unexpected. Mr. Plimsoll appears to find a difficulty in accounting for their existence at all, principally, perhaps, because he does not realise at how very high a pressure the gas is in the interior of our coal seams. And though there may not be large cavities in the surrounding rocks, nor in the seams themselves, there are fissures large enough, when filled with gas at such pressures as we find from experiment to exist, to form more violent blowers than any I have myself encountered. And when it is remembered that a safety-lamp cannot be depended upon in a very rapid current of fire-damp, the great danger arising from these blowers will be readily understood.

That there are other parts of a mine in which an explosion is more likely to occur than in the goaves is no ideal conclusion. The Committee, whose opinion I have already referred to, report that, during the fourteen years which immediately preceded the Haswell accident, there have occurred eleven great explosions in the Northumberland and Durham collieries; and that these have happened, with perhaps one exception-though that one is of a doubtful character-where the respective mines were being worked in the whole; that is, in those parts where pillar-working had not yet been commenced. It is, therefore, clear that, in at least ten cases out of eleven, during the period in question, the goaves have had no connection with the origin of these accidents.' We see therefore that, even were it possible to drain the goaves of gas quite effectually, we

should still be liable to explosions, and that we must seek in another direction for anything like a radical cure for these disasters.

Under such circumstances, it is with very great diffidence that I venture to make any suggestion of my own; but an examination of the story of the different explosions, as told in the Mines' Inspectors' Reports,' shows that in the vast majority of cases they were either caused by actual negligence, or that their origin has never been discovered. We may, I think, draw the inference that these last disasters also were, in many cases, due to carelessness; and-when it is remembered that, unlike all other trades, the lives of the miners are often in the hands of the youngest boy or most ignorant workman amongst them-it is extraordinary that accidents do not even oftener occur. For we must remember that, numerous and distressing as such accidents are, the life of the collier is, after all, safer than that of most persons employed in other of the more dangerous trades. The merchant seaman, the railway servant, or even the sailor in our Royal Navy runs greater risks.3

I do not indeed, for my own part, anticipate that the better education of our miners, desirable as it is on other accounts, will have any very great effect in reducing the number of explosions; we may be assured there must always be some careless and ignorant amongst the large body of men required for the working of a mine. I would rather that scientific men should turn their attention to some cure not depending for its success upon the carefulness of the workmen as a body, and depending as little as possible even upon the carefulness of their employers, for the most careful and experienced must sometimes fail. But we know that fire-damp, until raised to a certain temperature, is not only inexplosive, but may be breathed for a time without ill-effects. Cannot our men of science give us light without heat? The first step in this direction has already been attained by the invention of luminous paint; another step, and the miner may be independent of lamp or candle, and an explosion cannot take place. If this be impossible, a new lamp, the heat from which cannot be communicated to the fire-damp through the neglect of its owner, would meet the needs of the case. Our present lamps, from the point of view of safety alone, for the light is but small, are almost all that can be desired in the hands of a careful person who knows how to use them; but we want a lamp equally safe in the hands of a careless or ignorant person. The electric light, so recently perfected

R

* During 1876, 11-428 merchant seamen lost their lives by drowning alone, 3-2 sailors in the Royal Navy lost their lives by all classes of accidents, and only 1.815 miners by all classes of accidents per 1,000 employed. During 1874 the proportion for railway servants was 3-703 per 1,000. See Proceedings of North of England Institute of Mining and Mechanical Engineers, vol. xxviii. p. 200. 1876 was a favourable year for miners; the number killed per 1,000 during the seven years ending 1879 is rather below 2; but even this compares favourably with the deaths in the other trades.

by Mr. Swan for household use, may assist us in the solution of this problem. A main feature of his lamp, and one specially noticeable in considering its adaptability to the illumination of mines, is that the light is secluded from contact with the outer atmosphere, is in fact in a vacuum, and if the vacuum be destroyed the light will go out almost immediately. The miner's lamp at present used depends for its safety upon a wire gauze which surrounds the flame; the air necessary for the combustion of the lamp passes freely through the gauze to the flame, and along with it the fire-damp, should any be present; but the flame cannot pass out through the gauze. Accordingly, though the fire-damp often explodes inside the lamp, where the quantity being small no harm is done, it cannot explode outside the lamp, where the quantity of course may be sufficient to cause a serious accident. Mr. Swan's light, being in a vacuum, can never come in contact with the fire-damp at all. A violent current of air which, as I have already said, will blow the flame of an ordinary safety-lamp through the gauze and thus cause an explosion should fire-damp be present, would have no effect upon a vacuum electric lamp. A defect in a safety-lamp may be easily overlooked, but a defect in Mr. Swan's lamp would extinguish it. In the case of fracture of the vacuum tube, while the lamp is lighted, there is almost a certainty of the simultaneous breaking and consequent extinction of the incandescent filament; but even supposing that this did not occur, all danger arising from this accident happening at the precise time and place when and where fire-damp is present in dangerous quantities, might be completely guarded against by the adoption of the expedient suggested by Professor Tyndall-the placing of the lamp in a glass vessel of water. A Swan lamp, thus protected, seems to me all that is required as far as safety is concerned; but it has two practical objections-viz. the expense and inconvenience of carrying wires about underground, and its want of portability. The first, I think, might be overcome. Can scientific men find a remedy for the second?

Shortly, there are, in my opinion, but two problems before us. We must either have light without heat, or a lamp so constructed that, without sacrifice of portability, its heat cannot be communicated to the fire-damp. These problems are no doubt difficult of solution, but I hope not impossible; for I feel assured that, so long as coal is mined from gaseous seams, no precautions that we can adopt, short of these, will provide a radical cure for explosions in collieries.

J. H. MERIVALE.

FIRE-DAMP.

THE great interest which Mr. Samuel Plimsoll has taken in the welfare of sailors has been very naturally extended to colliers, as shown by his article on Explosions in Collieries and their Cure' in the Nineteenth Century of December last; but as he disowns special knowledge of the subject, and states his object in writing to be that of starting on foot a systematic and painstaking investigation of the nature and relations of light carburetted hydrogen,' it would ill become me to criticise his paper except when pointing out errors which, from the circumstances of the case, clash with my argument.

It is of doubtful accuracy to say that much mischief arises 'because men will not learn, and will not obey, the physical laws of the universe.' Mr. Plimsoll must bear in mind that knowledge is progressive, and that science frequently suspects long before proof can be reached. Indeed, I am inclined to take a different view; for my practical experience tells me men will learn, and do obey, the laws of nature, when there is convincing proof, but they are slow before proof, and, for the sake of stability, rightly so.

The first great step towards the abolition of anything is to discover its source; and as light carburetted hydrogen, or marsh gas, called in the formulas of chemistry CH,, is the cause of explosions in collieries, we should find its origin; but whereas that was not practicable two years ago, it seems so now, and if I have not actually solved the problem, at least I am not far off doing so.

Let me first ask attention to the average of constituents in the construction of plants and coal :

Here we have before us a visible explanation in figures of the change

that has taken place during the process of carbonising. The proportion of carbon has almost doubled, and seven-eighths (3) of the oxygen, and one-half the nitrogen, have disappeared, leaving the hydrogen free to form hydrocarbon compounds, while the ash remains the

same.

Now what has become of the portion of gases shown in the plants, but which do not appear in the coal? Surely they are still in the coal strata, but in changed combinations, forming varied compounds of which the special object of our inquiry, carburetted hydrogen, is one.

The quantity of carbon which will combine with hydrogen is variable, and dependent on the degree of heat present. At a high temperature hydrogen combines with three times its weight of carbon, forming carburetted hydrogen.

I have now brought down my subject to two problems:

1. During the formation of coal was there sufficient heat to cause a combination between hydrogen and carbon, and, if so, whence is it produced?

2. What circumstances can arise to empower carburetted hydrogen to rush out of the strata with enormous velocity?

Now as to the first. During fermentation great heat is evolved, and that must have been the case in the formation of coal; whether sufficient I am not prepared to say, but there has been another source of heat. Every coal-field has at some period been overlaid by strata which denudation has removed, perhaps 10,000 feet more or less; in which case the heat due to depth would be about 140° Centigrade = 284° Fahrenheit, which would give a pressure of three and a half atmospheres, or, say, of steam 54lbs. on the square inch.

As to the second problem, the matter is of great interest; for the question involved is the vaporising, liquefying, and solidifying of

gases.

In order to apply this, it must be understood that the only difference between a gas and a vapour is of degree-a gas being only an attenuated vapour, and a vapour a condensed gas, the visible change resulting from falling temperature or pressure, or a combination of the two.

Carbonic acid gas will condense by the pressure it evolves during. generation in a strong closed vessel, and commences to do so when compressed into one thirty-sixth (3) of its volume. If a valve in the vessel be suddenly opened, snow-like flakes will be formed at a temperature of about -80° C., which is solid carbonic acid, or, in more scientific language, solid carbonic dioxide; but the greater quantity resumes the gaseous state. Now the same law applies to all gases; and since oxygen, hydrogen, and nitrogen have been either vaporised