feet of air unfit for respiration. If an excess of air or fire-damp were present before explosion, such excess would remain mixed with the after-damp after the explosion, but in no case can the after-damp gases contain more than one-third of their volume of unchanged air, or the explosion would not have happened. After-damp is sometimes responsible for more deaths than an actual explosion, as often all that escape the latter are suffocated by the former, indeed, Dr. Haldane's investigations on the bodies of those who had been killed in three serious explosions led him to strongly assert that in almost every case the actual cause of death was poisoning by carbon monoxide.* It seemed probable that many men must be killed by absence of oxygen in the after-damp, and many others by burns or violence, but analysis of the blood showed that this was not the case. It would seem that the after-damp is so largely diluted with air, that more than enough of oxygen is left to support life. From 60 to 70 per cent. of the bodies were neither burnt nor injured, and taking the average of the three explosious it seems probable that about 77 per cent. might have escaped but for the after-damp. From the analysis of blood from the bodies found along the course of the explosion at Tylorstown, it may safely be concluded that there was less than 3 per cent. and more than o'50 per cent. of carbon monoxide, about 1 or 1.5 per cent. would be a fair percentage.

A man who has been rendered unconscious from carbon monoxide poisoning suffers severely from the after-effects. If the exposure has been long he may die a considerable time after the blood has quite freed itself from the poison. The best remedy is the administration of pure oxygen, although it is of no avail against the after symptoms. Artificial respiration should be at once applied if the breathing ceases, and if the pulse be weak stimulants should be given.

Unfortunately, this deadly constituent of after-damp cannot be detected by the safety lamp, as its action on flame is inappreciable, except perhaps to cause it to burn a little brighter. Its presence can easily be detected by its action on the colour of diluted blood, but this examination cannot be made by artificial light, and is consequently inapplicable underground. Dr. Haldane suggests that the effect of the action of the impure air current on a small warm-blooded animal, such as a mouse, should be carefully noted, as immediately it shows weakness of the legs there is danger to a man, though probably not for twenty minutes or half an hour. A mouse is not more sensitive to carbon monoxide than a man, but it shows the symptoms of poisoning in about one-twentieth of the time. If the mouse becomes quite helpless and unable to stand, there is danger within a few minutes to the man. It should be clearly understood that this test cannot do more than indicate the presence of dangerous proportions of carbon monoxide, and only a practised observer could detect the outward signs of slight symptoms in a mouse, while correspondingly slight symptoms in a man might be distinctly felt by the subject of them. As the specific gravity of after-damp must be, if anything, lighter than air, it is desirable to add a caution as to the desirability of keeping the animal as high as the head of the man carrying it.

Mr. A. Mermet† suggests the use of a prepared solution containing small quantities of permanganate of potash, silver nitrate, and pure *Fed. Inst., xi., 502. + Coll. Guard., 1897, lxiii., 771.

nitric acid as a preservative. This is exposed to the action of air from the mine, and a similar quantity also exposed to ordinary air at the same time, the two flasks containing the solution being put side by side on a sheet of white paper. The impure air decolorises the solution, I part of carbon monoxide per 500 to 5000 parts of air acting in from one to twenty-four hours. Such a test is too slow to be of any value to a rescuing party.

Coal-Dust.-The roadways of some mines contain accumulations of very fine coal-dust scattered over the timber and resting on the floor, this being more particularly true of the main haulage roads. Several hundreds of tons of coal pass down these in trams or tubs day by day, and the lumps are ground and shaken against each other, more so when the speed of hauling is high, while the speed of the air current is also greater than in branch roads. Deep mines should theoretically be dustier than shallow ones; the temperature of the strata is higher, and consequently the intake air is heated more than it would be in a shallow mine, and is really drier, because it is able to absorb a larger quantity of moisture before becoming saturated. The air current thus dries the dust and blows it about, the lighter and more dangerous particles being carried on to the roof timbers and the remainder to the sides and floor, the latter being the least dangerous. These accumulations can be prevented to a great extent by exercising ordinary care in using tubs with close sides, and seeing that they are properly emptied at the surface, and not sent back into the mine with quantities of small coal in them, and by watering the broken coal in the tubs, as described later on. That such deposits may be prevented from accumulating, is established by the fact that they exist in minimum quantities at or near the working face, and increase in thickness towards the shaft. From observations made at Cinder Hill Colliery, a perfectly dry mine, which has been opened fifty years, Mr. G. Fowler states that the film of dust is insignificant for 900 feet back from the face, which represents the distance worked out in three years, and shows that for that length of time the accumulation of dust is scarcely noticeable.

Messrs. Faraday and Lyell, in a report on the Haswell Colliery explosion in 1844, were the first to demonstrate the effect these accumulations of dust may have in extending fire-damp explosions. Although several persons investigated the matter. it was not until 1876, when Mr. Wm. Galloway read his first paper before the Royal Society, that general attention was directed to the important part that coal-dust plays in aggravating fire-damp explosions. Subsequent experiments by Mr. Galloway, by several members of the North of England Institute, § a committee of the Chesterfield Institute,|| Sir F. A. Abel, and particularly by the Prussian Fire-Damp Commission,** demonstrated that, under certain conditions, the presence of coal-dust

+ Fed. Inst., xi., 129.

+ Proc. Royal Society, March 2, 1876, xxiv., 239.

Ibid., xxviii., 437 and 490, and xxxvii., 42.

§ N. E. I., xxv., 239, and xxviii., 85.

Vol. x., with Appendices.

Blue-Book, Seaham Colliery Explosion, and Proc. Royal Institution, x., Part

I., 1882.

** Translation by T. W. Bunning, N. E. I., xxxiv., 199 and 297.

in a fine state of division is a source of danger in dry mines in which blasting is carried on without special precautions.*

Upwards of 300 experiments were made by the Prussian FireDamp Commission at Neunkirchen, near Saarbrücken, and it was considered that the following conclusions were warranted by the results obtained: †

1. The presence of coal-dust in more or less abundance in the immediate vicinity of the working face, gives rise to more or less elongation of the flame projected by a blown-out shot, whether small quantities of fire-damp be present in the surrounding air or not.

2. (a) In the complete absence of fire-damp, the elongation or propagation of flame is generally of limited extent, however far the deposits of dust may extend in the mine ways.

(b) There are, however, certain descriptions of coal-dust which, if ignited by a blown-out shot, will not only continue to carry on the flame even to distances extending considerably beyond the confines of the dust deposits, but will also give rise to explosive phenomena or results, in the complete absence of any trace of fire-damp, which in character and effects are similar to those produced by some other dusts in air containing 7 per cent. of fire-damp.

3. (a) All the phenomena produced by the burning of and propagation of flame by coal-dust are intensified by the presence in the air of small proportions of fire-damp.

(b) Certain dusts which, under favourable conditions, appear to have the power of propagating flame to an indefinite extent in a dust-laden area, the air being free from fire-damp, will, if only sparsely suspended in air containing fire-damp in some proportion below 3 per cent., render such a gas mixture susceptible of explosion by a blown-out shot. 4. Special experiments in which the branch gallery, described as opening into the main gallery near its extremity, was charged with a fire-damp mixture (retained by brattice cloth), demonstrated that a coal-dust ignition or explosion, developed in the complete absence of firedamp, can communicate ignition to an explosive gas mixture existing at a very considerable distance from the point of first ignition.

Special stress was, however, laid on the fact that the occurrence of a blown-out shot is indispensable to the production of any and all of the effects (of ignition, propagation of flame, or explosion) to which coal-dust can give rise; and Mr. Hilt emphasises the fact that the part played by coal-dust is not nearly so dangerous as it might appear from a superficial examination of the Saarbrücken experiments.

Messrs. Mallard and Le Chatelier, in a review of the work of the Prussian Commission, consider the phenomenon of the ignition of coal-dust by a blown-out shot to be as follows:--In that part of the gallery reached by the powder gases travelling at a high velocity and endowed with a high temperature, the dust is violently thrown into suspension and ignites. The gaseous mass thus ignited (considerably expanded by heat and increased by the partial distillation of dust that has been thrown into suspension by the mechanical effects of the powder shot) expands into the gallery, and extends to a distance proportional to the mechanical effects of the powder gases and to the ease with which the dust in suspension is distilled. The mechanical effect of this jet of flame on the dust in the gallery, situated at such A complete review of the literature of the subject with extracts of the opinions held by English authors, is given by Mr. E. S. Hutchinson in a paper entitled "Notes on Coal-Dust in Colliery Explosions," Amer. Inst. M. E., xiii., 253. + English Commission on Accidents in Mines. Final Report, 1886, 43. Ann. des Mines (8 Série), ix., 638.

a distance as to escape the initial action of the powder gases is small, and rapidly decreases until it is destroyed at a very short distance from the shot. They consider that the experiments of the Prussian Commission confirm these opinions, and also their previously expressed ones, *that the combustions of dusts are not, to speak exactly, explosions; that combustions only produce mechanical effects entirely insignificant for most dusts, and always much less than fire-damp explosions, even for most exceptional dusts; and that the combustion produced at any point does not extend indefinitely over the whole area covered with dust.

On the other hand, the English Commission on Accidents in Mines† considered that the most emphatic refutation of Messrs. Mallard and Le Chatelier's conclusion, "that the influence of fire-damp upon the combustibility of dusts, if not altogether nil, is at least much slighter than was at first believed," and confirmation of the established facts which it combated, was furnished by the Saarbrücken experiments, and, after a review of the whole subject, considered that the following facts relating to the part played by dust in coal-mine explosions may be regarded as conclusively established :

1. The occurrence of a blown-out shot in working places where very highly inflammable coal-dust exists in great abundance may, even in the total absence of fire-damp, possibly give rise to violent explosions, or may at any rate be followed by the propagation of flame through very considerable areas, and even by the communication of flame to distant parts of the workings where explosive gasmixtures, or dust-deposits in association with non-explosive gas mixtures exist.

2. The occurrence of a blown-out shot in localities where only small proportions of fire-damp exist in the air, in the presence of even comparatively slightly inflammable, or actually non-inflammable but very fine, dry and porous dusts, may give rise to explosions, the flame from which may reach to distant localities, where either gas accumulations or deposits of inflammable coal-dust may be inflamed, and may extend the disastrous results to other regions.

That the above conclusions are true is now generally admitted, and the importance of adopting some effectual means for dealing with dust-deposits becomes self-evident when it is remembered that the most practised observer cannot detect gas in the air currents with safety lamps when the proportion present does not exceed 2 per cent.

It is, however, contended, more prominently by Mr. Galloway and Messrs. Atkinson, that coal-dust plays the principal part in colliery explosions, and that fire-damp must be relegated to a secondary position. The chief argument in favour of this view is that explosions are so often confined to the intake air-ways and not to return air-ways. The intakes are where dust collects owing to the haulage of coal, while the returns are those along which gas is carried off. It is also contended that gas explodes equally in all directions, while many explosions in mines do not seem to pass into all the routes equally open to them, but follow certain definite paths, such as intake airways where gas is absent but coal-dust present. An explosion that took place in a coal-hopper at Brancepeth Colliery, Durham, where no gas could be present, is also quoted as an argument in favour of this theory. This hopper was used to store coal in for the use of the coke ovens. It was being cleaned out, when the fine dust took fire at an open torch lamp. Several men were severely burnt and three lost Ann. des Mines (8e Série), iv., 274. + Final Report, 47.

Explosions in Coal Mines, London, 1886.

their lives. It may, however, be taken more as an instance of ignition than of explosion, as, although several windows existed in the hopper, none of the panes of glass were blown out, although they were much cracked by the intense heat. Only one sheet of corrugated iron was burst off the box, and this was not blown away, but was simply dislodged and fell to the ground.*

The theory is supported by the fact that explosions happen in flour mills, and in the drying chambers used for the preparation of brown coal for the market. It has also been proved by large explosions which have taken place in flour mills at Annapolis, U.S.A., that in the entire absence of inflammable gas, the explosion beginning in a distant portion of the works may be carried through the entire building. It is also possible, experimentally, to obtain explosions with air and lycopodium, simply with the lycopodium lying on the floor and not forming a thick cloud.

The great argument against coal-dust being the principal agent in coal mine explosions, as pointed out by the English Commission on Accidents in Mines,† is the fact that, if it were so, every blown-out shot occurring in a very dusty and dry mine should actually be attended by a more or less disastrous explosion or conflagration; and that, looking therefore to the enormous amount of powder expended in shot-firing in this and other countries, and to the not inconsiderable proportion which blown-out shots must constitute in many localities, of the total number of shots fired, disastrous coal mine explosions should be of more than daily occurrence, if this view were correct.

Messrs. Mallard and Le Chateller maintain that all explosions of magnitude which have been solely attributed to coal-dust have occurred in mines in which fire-damp occurs; that the possibility of coal-dust, per se, giving rise to an important explosion could only be established by the occurrence of an explosion in a mine in which the total absence of fire-damp can be absolutely demonstrated; and by the fact that lignite mines, which are generally very dusty, the dust being extremely inflammable, but which are at the same time almost free from fire-damp, have never yet been visited by accidents of this class.

In Chapter i. reference was made to the experiments of Mr. J. W. Thomas on the gases enclosed in coal. Dr. P. P. Bedson has conducted similar investigations on coal-dust, and has established the point that some dusts give off considerable volumes of explosive gas at a comparatively low temperature. The enclosed gases in coal-dust resemble in many respects those which have been obtained from coal. The main points of difference to be noted are-first, the large proportion of carbon dioxide (CO2) as compared with the amounts found by Mr. Thomas, and, second, the presence of olefines and higher members of the paraffin series of hydrocarbons. Further experiments by Dr. Bedson and Mr. McConnel§ showed that not only is the greater portion of the occluded gases given off at the temperature of boiling water, but that this is more emphatically true of the combustible gases, while it is evident that mechanical subdivision of the coal favours the release of these gases to a marked extent. They also established the fact, that the denser hydrocarbons are more firmly held than the

* Royal Commission on Coal Dust, First Report, 108. + Final Report, 47. + A Contribution to our Knowledge of Coal-dust," N.E.I., xxxvii., 245. § Fed. Inst., vii., 27 and 32.