852 THE COLLIERY GUARDIAN. April 25, 1913. incombustible dust into a mine for the purpose of lessening the danger of coaldust would not, even if Abel’s contention was correct, introduce a source of danger that was not already present. For, whatever the incombustible dust could do in promoting gaseous explosions, coaldust could do much more effectively. Whatever danger of gaseous explosions may exist already by reason of the presence of coaldust, it certainly will not be augmented by the addition of incombustible dust. We are, however, of the opinion that incombustible dusts do not have the effect attributed to them by Abel, but have a distinctly con- trary effect. We do not, therefore, apprehend any increase of danger from gas explosions by their intro- duction into mines. The facts above set forth appear to us to dispose of one of the points which we mentioned in our First Report as requiring further investigation. Experiments with incombustible dust have been made, and are now being made in the large gallery, and we hope soon to publish an account of them. 60 1OO 60 o a 'a. 20 a. One gram of platinum black in suspension. b. No dust in suspension c. Half a gram of calcined magnesia in suspension d. Five grams of calcined magnesia in suspension Fan running at a speed of 6,000 revs per min m each case. Time — seconds. (Time 0 — time of first appearance of pressure.) Fig. 4.—Explosions op Ethane and Air. Ethane - 4*05 per cent. I M cs D 3 £ d 20 60 O a S’ & a. No duet m suspension b. Tbree-and-a half grams of platinum black in suspension. Fan running at 6,000 revs, per mm in each case. Time — Seconds. (Time 0 = time of first appearance of pressure.) Fig. 5.—Explosions op Ethane and Air. Ethane = 4’15 per cent. Having thus found that inert dust had a retarding effect upon the ignition of mixtures of gas and air, it occurred to us to try whether inert dust could stop an explosion of gas and air which had already formed and was in progress. We found this to be the case in a series of preliminary trials (a summary of which is given in Appendix III.). It would be premature to draw conclusions from them until they have been repeated on a larger scale. Note on the Second Report. We stated in our Second Report that Prof. Bedson, who has distinguished himself by such valuable work in connection with the coaldust theory, had shown that a considerable proportion of many coals can be separated from the main bulk by the solvent action of pyridine, and that the extract thus obtained was very inflam- mable, and a reference was given to Transactions of N. England Mining Engineers, 1899, p. 82. Prof. Bedson also wrote a paper on the subject (Transactions of N. England Mining Engineers, vol. 39, p. 719), in which he demonstrated that this pyridine extract is more inflammable than the coal itself. The experiments alluded to in our Second Report have shown that the inflammability of the coal as a whole is nearly proportional to the quantity of the coal that can be dissolved by pyridine, and thus extended Prof. Bedson’s results, so as to substantiate our opinion that the relative inflammabilities of different coaldusts depend, not on the total content of volatile matter, but upon the proportions which they contain of the most readily decomposed constituents. SOUTH STAFFORDSHIRE AND WARWICKSHIRE INSTITUTE OF MINING ENGINEERS. A meeting of the above institute was held at the University, Birmingham, on Monday, April 21, the President, Dr. J. Cadman, in the chair. The following gentlemen, having been approved by the council, were elected:—As members: Mr. A. P. Catherall, Mines Department. Trinidad; Mr. G. W. Sou th worth, Rivington, Harden-road, Bloxwich, Wal- sall. As student: Mr. J. Rudowski, Freiberg-i.-Sa., Stollngasse. Electrification of the Cannock Chase Colliery. The President then called upon Mr. S. F. Sopwith to read his paper, “ The Electrification of Cannock Chase Colliery.” (The text of this paper appears on p. 847.) In the discussion that followed the reading of the paper, the President said they were very much indebted to Mr. Sopwith for his paper. The question of colliery consumption was one of the most important of the problems which the mining engineer had to attack at the present moment, and Mr. Sopwith had very boldly brought forward all the figures and details, which, he thought, reflected very great credit upon him, and which they highly appreciated. If mining engineers would give them the benefit of figures of that sort, many defects would be avoided. Mr. J. Brindley said he could not help thinking there were other matters with regard to carrying out improvements and for cheapening production than the adoption of electricity in this case. He noticed that the figure ran out at practically Id. per unit, and he (Mr. Brindley) would not have had any criticism to offer if the author had got power at £d. per unit. Of course there was no power company available on Cannock Chase, which was rather a pity, and there appeared to be very good scope for a company supplying power in that district. He understood that the pits in the area were somewhat scattered, and it might be that the electrification had been done in the best way, but it seemed to him that it might have been done in a better way, and he could not help thinking that there was an enormous loss in carrying out that plan. He did not suppose that the useful effective power would be more than 15 or 20 per cent, when it was all over. Mr. Sopwith had not touched upon the point that he (the speaker) expected him to deal with—namely, as to whether it was more convenient and comfortable to use electricity, and nothing was said about steam. Then, again, he did not consider that 10 per cent, allowance for depreciation was anything like enough for electrical plant. In three or four years’ time it would be out-of- date altogether and would have to be scrapped. He believed that it was the usual thing to make an allowance of 30 per cent, for plant of that description. Although it was an interesting experiment, he was not at all sure that upon the evidence of that paper elec- tricity was something the colliery manager ought to rush for, and it seemed to him that the better way was first of all to improve their existing steam plant. A great deal of the plant in existence was very ancient, in some cases employing high-pressure steam, and it might be possible to adopt condensing arrangements and apply rope-haulage for long distances before jumping into an expenditure of £21,000. They might follow the example of Holly Bank and improve their steam plant, or wait until there was some chance of electrical power coming along to be supplied to them at |£d. per unit or there- abouts. Mr. Alexander Smith said he thought it was very proper of Mr. Sopwith to give them the benefit of his experience, because in doing so he was only following in his father’s footsteps. He believed, if he remembered rightly, that Mr. Arthur Sopwith was the first to intro- duce electric light in the collieries of the Midland district. He thought Mr. Brindley had forgotten that Mr. Sopwith had to deal with old straggling collieries, and he had to do what he considered was the best under the circumstances, and on the whole he appeared to have secured fair results. He was in the position that he could not go to a power company, and it was very unfortunate that he could not get some of those com- panies they had heard of who supplied power at, surely Mr. Brindley would not claim, a farthing per unit under ordinary conditions, so he would say about a halfpenny. He (Mr. Smith) had known a company offer to supply power at 0’4d., but that company never paid a dividend and he did not think it ever would. He questioned whether any of those other companies who were supplying at the same rate would pay a dividend. But a colliery company worked on different principles, and expected to get results from the money expended. Mr. H. H. Ridsdale said he noticed that the power station given in the paper had a total capacity of 900 kilowatts, and a little later in the paper he showed a normal load of 350 kw. He took it that Mr. Sopwith was working with a 500 kw. generator and the other two 200s in parallel. The load was practically one-third, and he understood that the other 200 was simply a stand-by. Mr. Sopwith evidently had a very low power factor, and it was clear he must have unless he was working haulage motors and everything else up to the hilt. It would be a better arrangement if he could so work the generators that they would have been approxi- mately working equally in turn. Mr. Bernard Clark said that in comparison with the size of the plant the load factor was distinctly small. But they had to consider the distance the power had to be transmitted, which must bring up the cost. As regards this proportion of power obtained to the power put in, or, in other words, the final result in power of the power put into the generator, one gentleman ventured to say that would be as low as 15 per cent., but he (Mr. Clark) would venture to put it as high as 40 per cent. He had figures before him dealing with a colliery installation where it was as high as 50 per cent. As a matter of interest he had made a small comparison with a colliery which had a fairly large generating station, and which generated its power from an exhaust steam turbine and boilers, exactly the same as Mr. Sopwith did. But theirs was a much larger plant and a better load factor. He would give those figures for comparison. The output was 81,000 units per week, compared with 15,000 units at Mr. Sopwith’s plant. The cost of generating was divided under two heads— first coal, wages and stores, which came out at 0’18d.; and .secondly, capital charges and sinking fund was also 0’18d., making the total cost of generating of 0’36d. against Mr. Sopwith’s 0’516d. Adding other charges they got 0’471 for capital charges and sinking fund, making a total of 0’987d., or practically Id. per unit. The total capacity of the station he referred to was 5,000 kw., whereas Mr. Sopwith’s total capacity was 900. The load factor of the large station was 50 or 60 per cent., but their load factor was large because they had pumps working day and night, coal-cutters, &c. In Mr. Sopwith’s case 15 to 20 per cent, was the load factor. In the other case the normal load was very high—much higher in fact, being 3,000 kw. against Mr. Sopwith’s 350. Another point had a rather striking fact was that per pound of coal in the case he had mentioned they got 500 units against 224 in the Cannock Chase Colliery. That, of course, was due to a certain extent to the fact that it was South Wales coal. In fact, the actual coal used was “ washed beans.” Mr. J. R. Felton, H.M. inspector of mines, said he had seen the plant several times, and he agreed with Mr. Bernard Clark that there was some praise due to Mr. Sopwith for the plant that had been installed. The cost per unit appeared to him to represent a quite satisfactory result, having regard to the load factor of 15 to 20 per cent, and the normal load. He thought that some of those power companies that had been referred to—and especially one in the north of England which supplied current so cheaply, at something under |d. per unit—were using flue gases for the generation of power, and that must have a good deal to do with the reduction of the cost. At the same time he thought Mr. Sopwith’s paper would have been much more interesting if he had gone into more detail in regard to the plant, particularly as it was, so far as he knew, the first in the southern part of the county dealing with high voltage. He knew that in North Staffordshire there were a few such plants, but he believed this was the first in the south in which the generation of power was anything like 3,000 volts. The author had said nothing about the earthing arrangements, although that would have been very interesting information. Mr. G. M. Cockin said the different points under- ground which that central power station supplied were a very long way apart, and the conditions were extremely difficult, and he understood that it was not so much a question of reducing costs as a means of working coal which could not have been got otherwise. Mr. S. L. Thacker said he did not think the depreciation charged was insufficient, because, if they examined the items upon which it was charged, they would see that practically a third of the capital outlay