agreed with Mr. Steavenson that this was specially a paper for their Transactions, and he thought it proved the value of the Federated Institution that so valuable a report could be put in the hands of so many who would not otherwise have had access to it. He begged to move a vote of thanks to the Durham Coal Owners' and Miners' Associations for the permission they had given for it to be printed in the Transactions.

Mr. W. N. ATKINSON seconded the motion, and it was adopted unanimously.

The PRESIDENT said he hoped the discussion would be renewed at their meeting in Birmingham. There were so many things in the paper that they could not at all comprehend by once reading over. On the present occasion, however, the very cordial thanks of the meeting were due to Professor Bedson for the way in which he had conducted these experiments, and brought before them the result of his great work.

Mr. A. SOPWITH seconded the vote of thanks, which was carried unanimously.

Mr. H. HALL (H.M. Inspector of Mines) read the following paper on "Coaldust":

COAL-DUST.

BY HENRY HALL.

Perhaps no subject in connexion with mining has attracted so much attention during the past fifteen years as that of coal-dust. When attention was first directed to its possible dangers, either in conjuction with fire-damp, or per se, the views advanced were received almost with ridicule, and by many the "coal-dust theory," as it was called, was looked upon simply as a "red herring" useful only to divert attention from other unpleasant aspects of colliery explosions.

Gradually the dangers of dry coal-dust have received more serious consideration, and now the author ventures to submit that the consensus of opinion among mining authorities is that its dangers are such as demand speedy and energetic treatment.

We are most of us familiar with the results that have been obtained by means of experiment by various commissioners, committees, and individuals to elucidate this subject. Those experiments and results have conclusively shown that wherever dry coal-dust exists in underground workings in such a mechanical condition that its finer particles can be lifted and carried by the air passing along and lodged on the sides and roof or bars of the workings, an explosion of dust, per se, or with small admixtures of fire-damp, otherwise harmless, is possible.

The ignition and explosion of dust in the entire absence of fire-damp by gunpowder shots, and by an initiatory explosion of a fixed quantity of fire-damp, have again and again been effected in long galleries prepared for the purpose, and its ignition, when a small and otherwise harmless amount of fire-damp is present, is a certainty at almost every attempt.

The writer, by means of some recent experiments in an actual mine shaft, has endeavoured to remove any doubt that might exist as to the conditions in experimental chambers being the same as those present in the mine itself.

The point which appeared to him to deserve most attention was whether or no an ignition of coal-dust in a "mine-working" could obtain such a ready supply of air as to ensure a sufficiently rapid combustion as would give an explosive effect, or, in other words, whether in a mine the ignition of dust would "carry on" and travel over the whole or greater part of such workings where a supply of dust might be found.

Wherever artificial galleries of any length have been used for experiments, they were open to the objection that valves had to be inserted at intervals to relieve the pressure set up by the explosions for fear of the apparatus being destroyed; and it was just possible that such valves might be the means of supplying more air as the explosion travelled, which would not be forthcoming in an actual mine-working.

It is not necessary to detail here the writer's experiments, because they have already been brought under the notice of most of the members present.

The

drawing on the wall is a fair representation of the appearance of the top of the shaft, the result of a gunpowder shot blowing out into air saturated with coal-dust at a depth of 180 yards from the surface.

In very many of the great colliery explosions there has been no decisive evidence accounting for the great violence and damage over such large areas of the mines, scorching flames having passed along great lengths of roads, an effect, which if firedamp alone were implicated, seems almost impossible; and this in mines where the witnesses were unanimous that the workings were well ventilated, and fire-damp seldom if ever present in any serious quantity. It is, no doubt, natural on the occasion of an explosion in a colliery for the officials to endeavour to show as clean a bill of health as possible, but enquiries into such matters nowadays are close and exhaustive, and yet in many cases to an unprejudiced mind they have been far from convincing as regards the agency which has been at work. It must not for a moment be supposed that the writer wishes to convey the idea that there have been no disastrous explosions from large accumulations of fire-damp; such have, no doubt. occurred from time to time. All mining men are aware that mines are liable from temporary causes to be flooded with fire-damp, any accidental ignition of which would be fatal to the men underground in the colliery, and such accumulations take place most unexpectedly and from sources often the least suspected.

The importance of the phenomena relating to coal-dust consists in the fact that the conditions necessary to cause a disaster may continue to be present when a mine is thoroughly ventilated and free from fire-damp; and when we remember that what is termed "free from fire-damp" only means in practice that the atmosphere of the mine is so diluted that there is no visible evidence of the presence of this dangerous gas, and that some quantity more or less definite according as the seam is fiery or otherwise must inevitably be present, the subject assumes additional importance.

It seems almost remarkable that any doubt should have existed that a material such as coal-dust dispersed in warm air, once ignited, would fail to produce a rushing conflagration. Admitting, then, that this danger exists, the question arisesHow may it be met? Can dangerous accumulations of dust be avoided? Up to the present the only means which has attained partial success is the periodical application of water, either by means of sprays emitted through pipes at a high pressure along the roads, or by moving water tanks. The first of these methods promises the most success, and has been largely applied in South Wales and other districts, where its efficiency has been increased by the Martin process of blowing the water by means of compressed air; but this necessarily entails a double system of pipes, and is therefore expensive, and the moving water-tanks, which are not so costly, are objected to on the ground that they cause the floors to lift. Both of these systems fail to produce any appreciable effect at the face of the workings except in warm seams where there may be a reduction of temperature of a few degrees; they both add to the comfort and health of those engaged on the main roads, and must also reduce the amount of traction.

The system of pipes remains much as at first introduced; 2-inch main pipes, and smaller spray pipes with leaden plugs, are usually adopted. The leaden plug is perhaps recent, and enables the amount of spray to be readily manipulated.

Attempts have been made to saturate the air of mines with watery vapour, but without success. The writer is told that even in mills, where the area to be dealt with is much more limited, the saturation can only be effected up to a distance of a few yards from the source, and appears to be quite mechanical.

Iron or steel trams, and where wood is used, tongued and grooved boards, are effective to considerably reduce the amount of dust on the roads. The writer has been told that the change from plain boards to tongued and grooved reduced the dust to less than one-fourth of what it had been. Something can also be done by well watering the trams of coal before they are sent out, either by passing them under sprays or by means of watering cans. No serious attempt appears to have been made to deal with the dust systematically at the face of each working place-a course which would perhaps be the most natural one to adopt; but the writer has seen a longwall face dealt with by means of tanks of water and hand watering cans, the collier in each working being required to apply the water at intervals during the day, and the effect was considerable in allaying the dust and making the places more pleasant to live in; but the universal adoption of such a method would entail great expense and constant supervision.

Whether the dusts of different coal seams, when present in a similar mechanical condition as to fineness, are all equally dangerous, has not as yet been proved. It is possible that the danger may arise from the chemical constituents of the dust, and possibly, as pointed out by the Messrs. Atkinson, one mine might differ from another, or its chemical character may vary in the same seam, accordingly as the dust had been exposed a long or a short period to the influence of the atmosphere. The writer has collected samples of the lighter dust from the timbers of main roads, and also of that freshly wrought, and has had them analysed, with the following results:

"Dear Sir,―The following are the results of analysis of the two samples of coaldust received from you last week.

"As received, and without any drying, they gave :

Both samples yield a very low percentage of volatile matter, which has scarcely any illuminating power, and their coking properties are almost nil. Both these effects are such as might be expected in coal which has been exposed to the atmosphere for some considerable time. In No. 2 the amount of water is much greater than in No. 1, as also the amount of ash, which is very high. Reckoning as combustible the volatile matter, fixed carbon, and sulphur, it will be seen that whilst No. 1 contained 92.05 per cent., No. 2 only contained 79.54 per cent. After drying at 212 degs. Fahr. the samples gave the following ultimate analyses :

«No. 2 contains considerably more oxygen than No. 1, and if we deduct the ash the disproportion will be greater; as in No. 1 it will be 7.34 per cent. of the remaining constituents, while in No. 2 it is 11.09.

Henry Hall, Esq.,

H.M. Inspector of Mines,

Rainhill.

Yours faithfully,

RALPH BETLEY.

"N.B.-No. 1 Sample was collected from the screens above ground, and was freshly wrought. No. 2 was collected from the timbers underground, and had been a long time exposed to the atmosphere of the mine."

It is always much more easily practicable to accomplish an end when that end can be achieved by the discontinuance of an existing practice than is the case when additional duties are sought to be enforced, and the writer would submit that in dry, deep, and warm mines legislation requiring the workings to be constantly kept clear of accumulations of dust would be much more onerous and expensive than the compulsory abandonment of dangerous explosives.

If we elect to adopt "the abandonment of dangerous explosives," as being the most advantageous and most likely course to secure the object in view, viz., the reduction of disastrous colliery explosions to the utmost possible minimum, then it will be necessary to decide which of the various explosives possess features promising the greatest security. The writer has carried out a great number of experiments with different explosives, the most recent of which are here appended :