so-called flameless explosives, and they all produced flame and lighted explosive mixtures when the hole was unstemmed. With stemming, it was a different matter; it was possible to fire a gunpowder shot (if properly stemmed) without any flame; and before the last paper on this subject was read he had conducted some experiments with a view to finding out which of the high explosives was safest with a minimum amount of stemming. These experiments were not yet finished, but some of the explosives tested showed remarkable degrees of safety. Two or three were perfectly safe with 2 inches of stemming; others were not safe with 9 inches. He was not prepared to name at the present moment those which were almost absolutely safe and those which were dangerous. It would be invidious to do so in view of the numerous explosives in the market, as it was more a question for the Flameless Explosive Committee, who were about to commence their experiments.

Mr. D. BURNS said he would like to ask Dr. Bedson if he was in a position to state at what degree of compression of the atmosphere explosive mixtures might be ignited, and if sufficient force could be generated by the explosion, as suggested by Mr. Ross, to reach that degree of compression and developed heat? If Mr. Ross's contention was true-and there seemed to be a great deal of force in it-it did not become a matter of the flash or flame but of the explosion itself. There was certainly an explosive wave produced, and if that wave generated sufficient heat, it could ignite inflammable mixtures when it passes through them. Perhaps the reason of the experiments, in the shaft previously referred to, being so successful in causing a flame to come to the top of the shaft, was due to the fact that the air was not free to expand in all directions so as to allow the force to be dissipated, and being confined in the shaft, it was able to ignite the dust floating in the shaft. He had never thought before of inflammable gases being fired by compression produced by the explosive wave; and it seemed to be like fighting the air to try and get an explosive which would not ignite gas, unless, indeed, they could get such a slow explosive that an explosive wave would not be produced.

Mr. J. A. G. Ross said he was sorry that he had not the tables of heat produced by compression at hand, but they could easily be obtained. In modern artillery pressures of 14 to 20 tons per square inch were found, and in the old cannons it attained 30 tons per square inch. He presumed the pressure engendered at the mouth of the shot hole would be from 12 to 20 tons per square inch, and the temperature engendered from that would be tremendous. The advantage he saw in not producing flame was that the flameless explosive would produce an explosion merely at the aperture, whereas the others carried the burning points or solid incandescent particles to a greater distance.

Dr. BEDSON said the question was one which it would be beyond his province to explain. The enormous temperatures referred to as produced by explosives were, of course, on the assumption that the explosion took place in a closed vessel; such conditions would not apply to ordinary shot-firing either with or without stemming, as in consequence of the instantaneous expansion of the gases their temperature is greatly reduced.

Mr. M. WALTON BROWN said he had read the official record of the experiments referred to, and there seemed to have been no apprehension of gas being found in the shafts used for the trials. It was quite possible that there might have been gas present. In one instance the experiments were made in an upcast shaft, attached to a pumping shaft half a mile distant, and as the air appeared to reverse while the dust was being thrown down the shaft through a hand-riddle, it was possible, if any gas was given off in the mine, that the air might become sufficiently charged with gas so as to form an explosive mixture at the instant when the charges were fired. Mr. Steavenson seemed to think the experiments showed the explosive nature of the coal-dust in the shaft, but he believed that the flame only reached the top of the shaft in three out of six trials at the White Moss Shaft; that is, the flame extended a distance of about 60 yards from the shot, whereas in a colliery explosion the effects were felt, more or less, at very great distances.

Mr. THOS. BELL-Did it not blow the head gear down in one case?

Mr. M. WALTON BROWN said he did not think that the head gear had been damaged in any instance. It only appeared in three cases at the surface in the White Moss experiments with charges of 1 lb. of powder; in two cases the dust was not ignited, and in the other the dust was ignited, but the flame did not reach the top of the shaft. The second series of trials, made by Mr. H. Hall at the Southport Pit of the Haydock Collieries, were made in a sinking shaft 130 yards deep, connected with an adjacent sinking shaft by a short drift in a coal seam at a depth of 100 yards, where the cannon was placed upon a scaffold. Six experiments were made in this shaft, with charges of from 1 lb. to 14 lbs. of powder, and in every instance the coal-dust was not ignited. A third series of experiments were made at the Big Lady Pit of the Haydock Collieries. This pit is 210 yards deep, in which a scaffold, placed at a depth of 180 yards, supported two cannons. The downcast (a pumping) shaft was 21 yards distant, and connected thereto by two small drifts at depths of 180 yards and 210 yards respectively. The air in this case is reported to have been quite free from gas. Three sets of experiments were made at this shaft. In the first set, out of five pairs of shots in which from 2 lbs. to 3 lbs. of powder were fired, in three cases the coal-dust was ignited, and in two cases the flames appeared on the surface. There were six pairs of shots in the second set of experiments, in each of which 3 lbs. of powder were used; there were two cases in which the ignited dust did not appear at the surface; in the third case the flames reached the surface. In the last set of seven experiments, in which from 3 lbs. to 4 lbs. of powder were used, the dust was ignited in two instances; in the first the flame did not reach the surface, but in the second, in which 6 cwts. of coal-dust were used, and the last of the series, the flame and smoke issued from the shaft for five or six seconds. Mr. Hall's results could be summarised by stating that the coal-dust was ignited by heavy charges of blasting powder in twelve out of thirty experiments, and that the flame only appeared at the surface in six trials. In three cases the flame traversed a vertical height of 180 yards in a shaft of 8 feet diameter, and in three cases in a shaft of 7 feet diameter it attained a height of 60 yards. These

experiments appear to confirm the conclusions of Messrs. Mallard and Le Chatelier(1) that the combustion of coal-dust is not an explosion, and such combustion only produces in the case of most dusts unimportant mechanical effects, which are always inferior to those of gas explosions, even in the case of the most inflammable dusts; (2) that the combustion does not extend over the whole area covered with dust; (3) that the length of dust ignited in a mine is proportional to the intensity of the mechanical action which has raised and ignited the dusts; and (4) that this length is always limited, and in the case of blown-out shots of lb. of powder this limit does not exceed 65 feet for most dusts, and only reaches 200 feet in the case of very exceptional dusts. It will be recognised that in three of Mr. Hall's experiments, when 1 lb. of powder was fired the flames attained a vertical height of about (50 + 10 =) 60 yards; and when 11⁄2 lbs., 24 lbs., and 3 lbs. of powder were ignited the flames attained a vertical height of (180 + 13 =) 193 yards. It will be recognised if the flame of lb. of powder and coal-dust was transmitted to a horizontal distance of about 200 feet, that it would not be inconsistent with Messrs. Mallard and Le Chatelier's conclusions, if the flame of 2 lbs. to 3 lbs. of powder with coal-dust was experienced at a vertical height of 200 yards, in the case of a very exceptional dust. If the effects of lb. of powder are felt at a distance of 200 feet, by proportion, the effects of 24 lbs. might be reasonably expected to become apparent at a horizontal distance of even 1,000 feet. Mr. Barrett asked the effect of stemming upon carbonite. This question had not been tested in their joint experiments, which were specially made to test a statement of the manufacturers that carbonite was safe without stemming. He might, however, mention, in a general way, that exhaustive experiments made in Germany and France showed that the length of stemming had great effect in reducing the apparent temperature of the explosive and the possibility of the ignition of gas. One speaker suggested an explosive that could not produce flame; none of those invented up to the present time appeared to have reached that point. It was the fact that the ignition of a gaseous mixture required the existence of a certain temperature, and numerous experiments were being made to produce an explosive substance whose temperature of detonation would not reach that temperature.

The CHAIRMAN said that after this instructive discussion he would propose a vote of thanks to Mr. M. Walton Brown and Mr. W. Foggin for bringing so interesting a subject before them. He was afraid they had not yet reached the flameless explosive period, but trusted that the experiments which were being made would induce inventors to come forward, and that in time some explosive would be found which would be flameless. So far as he could see, if the water cartridge could be introduced it would be an effective way of "scotching the snake," but he did not know that the experiments with it had been very conclusive.

Mr. THOS. BELL (H.M. Inspector of Mines) said he had much pleasure in seconding the vote of thanks. He hoped the discussion would be adjourned, as there would be a good deal more to say about it.

On being put to the meeting the vote of thanks was cordially adopted.

ELECTRIC MINING SAFETY-LAMP.

The SECRETARY exhibited two electric mining safety-lamps, supplied by the Mining and General Electric Lamp Company, at the request of Mr. G. B. Forster, and read a report thereon by Professor Frankland. The smaller lamp weighed about 3 lbs., and would burn for upwards of 141⁄2 hours; the larger lamp weighed 4 lbs., and was made to run 7 hours. The light given by the two lamps was respectively one and two candles.

The CHAIRMAN-It seems to be the best we have seen.
Professor LEBOUR said the price was about 25s.

What is the price?

Mr. H. AYTON said he had tried one of these lamps, and instead of giving two candles, as it was supposed to do, it scarcely gave one.

Professor LEBOUR said it had been explained that the lamp Mr. Ayton tried had not above half the capacity of even the smaller lamp now exhibited.

Mr. STEAVENSON said one of the dangers of an electric mining lamp was that the man using it might be suffocated before he was aware of the presence of gas.

CHESTERFIELD AND MIDLAND COUNTIES INSTITUTION OF

ENGINEERS.

GENERAL MEETING,

HELD IN THE TOWN HALL, DERBY, JANUARY 10TH, 1891.

MR. JOHN JACKSON, PRESIDENT, IN THE CHAIR,

The PRESIDENT reminded the meeting that the Council had arranged for the General Meeting to be held in different centres, and in the ordinary course Derby had been selected for to-day. Judging from the number present, he rather feared the bareness of the agenda paper might in some degree be the cause, and he was sorry to admit that it was the blankest that had been submitted at any time in his recollection. Without papers the interest in the Institution must considerably fall off, and it naturally depended on the members whether that was to be so or not. Amongst their body were a considerable number of intelligent and clever men, who, if they would take the trouble and give the time, could furnish interesting papers on mining matters. He sincerely hoped that they were not likely to fall off in that direction, and that the number and merits of the papers in the future would be as gratifying as they had been in the past, and that those who were in a position to do so would help with contributions and supply material for discussion.

DISCUSSION ON MR. CHARLES SOAR'S PAPER ON "COAL-LOWERING ARRANGEMENTS AT GRANVILLE COLLIERY (SOAR'S PATENT)." The PRESIDENT said some comments upon this method of delivering coal into wagons were made at a previous meeting, and as Mr. Soar was now present any further questions upon the paper would no doubt be answered by him.

Mr. C. J. OLIVER (Grassmoor Colliery)-What sized coal is the largest Mr. Soar's apparatus will deal with?

Mr. SOAB-Say 24 inches long and 12 by 12; that is about the largest. Mr. H. LEWIS said he considered Mr. Soar's arrangement a very admirable one for dealing with tender coal, as it delivered the coal into the truck bottom without any fall. In the case of hard coal, which would stand tumbling about, it was another matter; but for soft coal it was a very good arrangement indeed.

Mr. J. BAGNOLD SMITH (Newstead Colliery) was of the same opinion. He said that some years ago he had to investigate a complaint from a customer in London-a

VOL II.-1800-91.

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