June 5, 191L THE COLLIERY GUARDIAN. 1255 down the shaft was already very troublesome on this score, without the addition of 50 per cent, of another dust. It might become difficult to work in such an atmosphere. At the same time, the idea was worthy of very careful consideration, and of being practically tested. Mr. Hugh Bramwell was inclined to think Mr. Hann was taking a rather sanguine view of this method of mechanical distribution of stone dust. One objection, he said, was that it meant increasing the already large number of mechanical appliances in mines. To have fixed one of these automatic distributors every 300 yards throughout the pit would be no joke. The probability was it would result in this work being done by hand. With regard to Mr. Hann’s 50 per cent, of stone dust to coal dust, how often did he intend to “ clean up ”? It seemed that he was going to make the roads unbearable, unless they were going to be watered, and once they commenced watering they practically did away with the utility of the stone dust. Personally, he believed that cleaning and watering, and as little stone dust as possible, was likely to be the best method. Mr. AV. T. Jones said they rarely heard nowadays the contention that stone dust in itself was effective : water- ing or spraying was also necessary. He believed the important part played by stone dust was by virtue of the amount of moisture it contained. He believed that a system of coal dust prevention was being tried at Tirpentwys by means of screen-spraying at the top*. Why not have a series of water screens underground at stated intervals, with a by-pass for men and horses, the journeys passing under these screens? They would serve to humidify the atmosphere, and both full and empty trains would be automatically sprayed. As to stone dust, was it possible to calculate the proportion of stone dust necessary to prevent an explosion? There were experiments going on all over the kingdom, and he knew of no single mine where stone dust was used to such an extent that it would prevent a coal dust explosion. His own experience showed that gas was a much more dangerous factor than was usually under- stood. He believed it was quite possible to ignite small volumes of gas upder certain conditions in the mine, which proved that the usual explosive mixture theory was not the last word on the subject. Preventive measures based on this theory was a doubtful standard of safety. Mr. John Roberts, Wigan, said with regard to igni- tions being produced with a lower percentage of gas than was usually assumed to be required, there was the factor of the smoky defective lamp to be considered. If they had only two or three per cent, of gas in a lamp that also contained a good deal of smoke, they might get an explosive mixture. The discussion was closed with a vote of thanks to Mr. Ashworth for his notes. Large Arches in Mines. In discussion on the paper on “ A Proposed New Method of Making Large Arches in Mines,” by Mr. John Roberts (Wigan)f, the President said the author suggested a method of constructing arches which differed considerably from the one usually adopted. It would be for members with practical experience to say how far this method would meet the difficulties usually encoun- tered, and whether it would lessen expenditure on this work, which, as they knew, was very costly. Mr. David Arnold Howell challenged the author’s claim that the method described by him was new in its application to tunnelling operations. He did not see how Mr. Roberts proposed to deal with his excavated material. The author mentioned that a “ line of rails is kept forward as the face advances ” for the removal of the debris, but whither he did not say. He (Mr. Howell) took it for granted that his top heading vas not at the same level as the main roads of the mine at the point in question, so that it would be necessary, in order to get at the top of the proposed chamber, to drive a shaft vertically upwards, or an inclined road up from the nearest, or most convenient, road, otherwise it would be impossible to get the excavated material away. To do this would weaken the ground around the chamber, and also increase the total cost very consider- ably. Mr. Hugh Bramwell said he thought Mr. Roberts meant his paper to deal with arching at the bottom of the pit : it hardly applied to arching on the ordinary road- ways in the mine; and he contemplated very large arches. For instance, he garve a width between side walls of 26 ft. If they were going to put in side walls 5 or 6 ft. thick, they might get dimensions of about 36 ft. wide. The only method of putting in such a huge place at the pit bottom would be in lifts or separate operations. Mr. E. A. Creed said when sinking a new pit he endeavoured to put in an arch that was as strong as the ground taken out. He put in arches 22 ft. in diameter, the stone, selected and dressed, being about 7 ft. thick. The arches were circular, and a good pillar was left. After about three years the arches kept their shape, but the stone pulverised. The depth was 520 yds. In another instance, at a depth of 650 yds., he put in stone side walls, and the crown of the arch was of steel girders, * See Colliery Guardian, April 3, 1914, p. 735. | See Colliery Guardian, January 30, 1914, p. 243. 10 in. by 6 in., elliptical in shape, the spaces between the girders being filled in with brick work about 4 ft. thick. The arches were 18 ft. 6 in. in diameter. His idea was that if the side walls gave in owing to side pressure, he would be able to support the crown of the arch. In two years the side walls had been changed three times. At first they had squeezed in to the extent of 7 in., but after a time the pressure eased oft. As the result of this experience he had found that brick side walls were better than stone on account of the better bond between the bricks. The cost of each girder was about L10, which was expensive, but the cost was amply repaid. Mr. Roberts reserved his full reply for the Proceedings, and the discussion was closed with a vote of thanks to him. The Coiling of Winding Ropes on the Drum. Mr. Hugh Bramwell, the author of this paper (which appeared in last week’s Colliery Guardian'), explained that for some years he had been running one of his com- pany’s pits with round ropes overlapping on the drum, and different people had made enquiries of him as to whether overlapping the round rope would suit their con- ditions. The chief purpose of the paper was to state the conditions in which it might be desirable to adopt such an experiment. Mr. A. E. du Pasquier, said he was glad to see the author referring in the paper to what he (the speaker) called the fallacy of the slewed pulley. Proceeding, Mr. du Pasquier said it was interesting to note that for two and three layer winding, where specially shaped strips could be fitted to the drum cheeks to push the rope over into its proper position, the life of the ropes was very satisfactory, but with four layer winding, where such strips could not be fitted for the last layer, the life of From Total cargo. ; Total bunker. 1913. 1914. 1913. 1914. Tons. Tons. Tons. Tons. Bristol Channel ports 346,102 329,051 21,244 21,283 North-western ports 295,818 211,610 65,095 61,914 North-eastern ports 685,306 648,518 33,154 29,618 Humber ports 231,628 81,944 14,029 5,320 Other ports on east coast 6,895 4,060 7,662 9,010 Other English ports 2,079 1,800 3,989 3,396 Total from England and Wales 1,567,828 1,276,983 145,173 130,541 Ports on east coast of Scotland 124,866 143,586 20,611 24,108 Ports on west coast of Scotland 123,718 139,753 48,187 34,122 Total from Scotland 248,584 283,339 68,798 58,230 Irish ports — — 4,462 4,838 Total from United Kingdom 1,816,412 1,560,322 218,433 193,609 The destination of cargo shipments was as follows:— the rope seemed to be appreciably reduced, the rope falling into the groove with a certain amount of shock. He asked Mr. Bramwell whether he thought the diameter of rope and diameter of drum had any influence on the question, apart from their fixing the maximum deflection of the rope. He (the speaker) could not see that they had any other bearing. A mathematical solu- tion of the problem would be, he thought, a little com- plicated, but the subject was one which would lend itself readily to experimental determination, and he suggested that Mr. Bramwell be asked to add to the value of his paper by constructing a scale model and making actual measurements of the maximum deviation permissible with two layer -winding, which was the practical point of interest, as grooving was a satisfactory remedy for any ordinary deviations. The matter should not be difficult to determine experimentally, as for any given angle of deviation the component tending to make the rope slip across the drum must be independent of the loading of the rope, and as the rope always led on tangentially to the drum, independent of the drum diameter, both these points could be readily determined by such an experi- ment, in the one case by changing the weights, and in the second case by using a wire of different diameter. The whole question of permissible rope coiling had a very important bearing on the general economy of winding engines; limitations imposed upon designers by objec- tions to greater deviations than 1 in 40, to the ropes overlapping in the centre of the drum, and to winding in two layers, all directly affected the economy of the hoist by increasing the inertia of the system. Mr. Bramwell had not referred to overlapping in the centre of the drum. It was, he (Mr. du Pasquier) suggested, an excellent way for enabling one to keep down the size of the drum, and as far as he had been able to ascertain, the increased wear of the lagging was not considerable, and if coiling on a steel barrel did not come in at all. Mr. G. W. Westgarth said he had seen many examples of good results accruing from overlapping both winding and hauling ropes. In his opinion the higher cost associated with the method was due to a consider- able amount of rope friction on the slant, and not to overlapping on the drum itself. The discussion was adjourned. Gas Testing in Cavities. The paper on “ A Few Practical Observations on Gas Testing,” by John Roberts, Wigan, and R. M. Evans (which appeared in last week’s issue), was then con- sidered. In the discussion, Mr. David Bowen, of Leeds, said that for given percentages of gas the heights of the caps depended very materially upon the kind of illuminant used, and the size and shape of the wick tube. He sug- gested that experiments carried out on various lamps, using different sizes and shapes of wick, and with different kinds of illuminants, should give important results. With regard to the systems of gas testing, a few years ago—prior to the period in which mine officials underwent systematic training in gas detection—he examined, as head of the mining department of the University of Leeds, over one thousand officials. He found that over 90 per cent, of them were unable to detect percentages of gas between 1-J- per cent, and 5 per cent, with a fair degree of accuracy, whereas, after systematic training, about the same percentage of the same men passed each test satisfactorily. The discussion was adjourned. Exhibition of Signalling Apparatus. Many colliery managers and engineers visited an exhibition at the South Wales Institute of Engineers last \yeek of signalling apparatus for mine shafts. The firms who sent types of apparatus intended to comply with the requirements of the new mines regulations were :— Adnil Electric Company, London; G. J. F. Black, Burton-on-Trent; John Davis and Son, Derby; Gent and Company, Leicester; Heyes and Company, Wigan; Meehan and Sons, Glasgow; Siemens Brothers, Wool- wi cl i: an d Gen era] Electri c Comp any, Lon d on. COASTWISE SHIPMENTS DURING APRIL. According to the monthly coal tables, the following were the coastwise shipments during April:— To ports in April 1913. 1 Tons. England and Wales......... 1,261,940 Scotland................... 123,010 Ireland ................... 431,462 April 1914. Tons. ... 1,106,105 ... 95,846 ... 358,371 Shipments to London during April aggregated 669,379 tons. CONTINENTAL MINING NOTES. Austria. Official Wholesale Coal Prices Vienna Exchange.—Pilsen large coal, 33-90 kronen per ton, in truck loads, ex Franz- Josef s Bahnhof. Ostrau-Dombrau-Karwin coals : Large 30-31 kr., cubes 29’60-30'60 kr., nuts 29-30 kr., small 23-23'20 kr., washed smithy coals 30-30'50 kr., coke 38-40 kr. per ton net cash, ex shutes. Nordbahnhof. Rossitz- Zbeschau-Oslav'an coals : Best smithy coals, washed, coarse or fine 30'50-31’50 kr., coke 30-32 kr. per ton, ex shutes Nordbahnhof or Staatsbahnhof. Upper Silesian coals : Best large or cubes 32'30-33'10 kr., intermediate large or cubes 31'50-32'30 kr., seconds large or cubes 26'70-27-80 kr., best nuts I. 32'70-33'50 kr., II. 29'60-30'10 kr., best smalls 23'50-24 kr., seconds 22'50-23 kr. per ton net cash, ex shutes Nordbahnhof. In truck loads : Best large or cubes 30'70-31'50 kr., best nuts 31’10-31-90 kr. per ton, ex Nordbahnhof. Gas coke from the Vienna Gasworks, 33'60- 34’40 kr. per ton, ex works. Lignites : Dux large 22’10- 23’60 kr., Brux or Dux cubes 22’10-23 60 kr., nuts 2160- 23-10 kr., Mariaschein cubes 24’10-25’60 kr., nuts 23’60- 25’10 kr. per ton, ex shutes Franz-Josefs or Nord west Bahnhof. Belgium. Social Insurance in the Mons District.—At the end of 1913 there were 3,655 aged .workers and 1,277 widows on the Mons fund, the total amount of pensions being 1,418,427 fr. Last year the payments exceeded by 110,421 fr. the amount of 2-J per cent, on wages charged to the owners, and this is defrayed by the province and the State. At a meeting of the Beeringen Company on the 12th inst., it was stated that the two shafts of the Kleine Heide Colliery, in the Campine, had been stopped on June 10, 1913, at 420 m., and on August 18, 1913, at 236 m. respectively, owing to water, necessitating the refreezing of the shaft walls.