170 THE COLLIERY GUARDIAN. January 28, 1916. The paper was illustrated by numerous lantern slides. The Chairman, in opening a discussion, said that in regard to the figures given of fatal accidents through shock, it would be interesting if statis-tics were given as to the number of accidents caused on a three-phase circuit where the neutral point was earthed. These figures were not usually given in the annual reports, but if they were, they would throw some light on the point whether the earthing of the neutral was beneficial or not. Mr. Sheldon’s remarks concerning gastight motors were interesting. In that district these motors were not absolutely necessary. At the same time, he believed it was quite as safe to work motors in mines as in factories, so far as that district was concerned. In fact, the conditions were often much better in the pit. With reference to the clearance between the rotor and the stator, personally, he would like to see a fair clearance in these motors, even if it did reduce the power factor. He did not think it was really of very much importance in a colliery plant. As to the cost of electric haulage gears, apart from the generating plant he did not think the cost worked out so much as in the case of steam gears. Endless-rope haulage was much to be preferred from the point of view that so much less motive power for a given output was required. Electric winding was becoming of great importance, and different systems were being well developed. The system to be adopted depended very greatly on local conditions. Where there was a small isolated colliery, the question of installing a generating plant and an electric winder was not a tempting pro- position, but whore, as in the case of collieries round Newcastle, where there were larger power plants from which the supply could be obtained, there was no doubt as to the advantage of installing an electric winder. A flywheel set in such cases was perhaps not worth the outlay, although it might maintain a better regulation. Personally, he was of opinion that a simple induction- motor winder would be more satisfactory. As a matter of fact, he believed that the largest winder in the country was on that principle. Mr. Beadsmoore, having thanked the society for the courtesy extended to the electrical engineers to take part in that meeting, alluded to the omission by Mr. Sheldon of the use of small haulages which could be worked in gates. As to the point of motor runs being made non-inflammable, all the permanent buildings around the pit bottom should be made a good job of, but in-bye they could not always do that. The motors there must be totally enclosed, as this would make them safe. In reference to electric winding, it was said there was not much scope for it in that district. There was, however, a direction in which he considered electric winding would be a distinct advantage, and that was in the case of outlying or emergency shafts. To have an electric winder at those shafts would be very advantageous. The power would be always ready, instead of having to get up steam in the boilers. Mr. Sheldon had made a point as to the difference in the torque between an electric wind and a steam wind. As to the steam wind the jerky torque might be due to the eccentrics, which were very close as a rule—any- thing from 10 to 15 degs. advance. If they were nearer, say, 30 degs., the winding would be much smoother. With regard to the switchgear, which had been shown in the illustrations, they, as mining electricians., had nothing much to complain of. He thought there was not much switchgear in use in that district but what complied with what Mr. Sheldon had said. Mr. >S. H. Lee denied that the torque was smoother in the case of an electric, winder than in the steam winder. He suggested that a flat balance rope would overcome the difficulty. Speaking of switchgear and motors in general, there were certain points raised by Mr. Sheldon which were very useful, such as th^ import- ance of doing away with rubber, or- anything which quickly deteriorated. Mr. S. A. Fox, referring to gastight and flameproof motors, stated that where gas was present, electricity should not be used, and it seemed absurd to go to that trouble and expense. The object was, of course, to make the motors as safe as possible, but in that district he did not think there was much use for them. Mr. Sheldon mentioned that a large air gap would have a poor power factor, but that was only true on low loads. Generally speaking, that class of motor with a large air gap would be more reliable and stable on overloads. In addition to that, the pull-out torque would be greater. Mr. Sheldon had described oil-immersed controllers, and suggested that it was advisable to do away with partitions between the rotor and stator contacts. He (Mr. Fox) understood that oil-immersed controllers had given much trouble by the sludging of oil. At a great many collieries liquid controllers were taking the place of oil-immersed controllers. As regarded winders, prac- tically nothing but liquid controllers was used. He did not agree with Mr. Sheldon that electric winders would cost more than the steam winders. The geared alternate current motor might be considerably cheaper than the steam engine in respect of first cost, but could not be used to the same advantage at collieries where there was not a big power supply available. A number of these gear winders were at work, and had proved to be efficient. They were particularly so in a long wind, but in a short wind they would not be so efficient, owing to rheostatic losses. Mr. Sheldon briefly replied to the discussion. He agreed with Mr. Beeston that it would be very interest- ing to have figures regarding accidents on a three-phase supply of an earthed neutral. He was pleased to hear from Air. Beadsmoore of the use which was being made of 5-horse power haulages in mines. He did not, how- ever, agree with him altogether as to eccentrics being the main cause of the jerky movement in steam wind- ing. He did not think it was so much due to the eccen- trics, as to having two cranks at right angles. It was interesting to hear that a flat rope would get over the difficulty. He agreed with Mr. Fox that explosive- proof motors were not necessary. As to liquid con- trollers, he was not quite sure whether they were not better than the resistance type. He could not endorse Mr. Fox’s opinion that the geared type motor was better than the flywheel set, as the latter enabled a wind to be completed in the event of a breakdown. A hearty vote of thanks was passed to Mr. Sheldon for his paper. THE UTILISATION OF ENERGY FROM COAL.* FUEL ECONOMY FROM A NATIONAL STANDPOINT. By Prof. W. A. Bone, D.Sc, Pli.D, F.R.S. The national aspects of fuel economy may be con- sidered from* two somewhat different standpoints, namely : (1) in view of the economic situation created by the war, and the necessity of enforcing a policy of national economy in the utilisation of essential commo- dities’ as the best means of paying a colossal war debt; and (2) in view of the interests of that remoter, but nevertheless not far distant, future, when our coal supplies will be restricted by approaching exhaustion. It can hardly be questioned that the chief material basis of the great industrial and commercial expansion of this country during the past century has been our abundant supplies of easily obtainable coal, which, until quite recent years, have given us a position of great advantage over all other countries. It is also equally true that we can no longer claim any advantage in this respect over our two nearest competitors, and that our whole economic future is dependent on our ability to maintain abundant supplies of relatively cheap fuel, which in turn is limited by the probable duration of our easily workable coal seams in relation to present and future demands. According to an exhaustive report on the world’s coal resources issued by the International Geological Con- gress in the year 1913, the total probable and possible reserves of coal of all kinds (including anthracite, bitu- minous coals, and lignites) available within 6,000 ft. of the earth’s surface, are estimated to be 7,397,553 million tons, or approximately 6,000 times the present total annual consumption. Therefore, the world, as a whole, need have no fear of any speedy exhaustion of its coal supplies. Of the estimated total reserves, 6-75 per cent, are anthracites (mainly located in China), 52-75 per cent, are bituminous coals, and 40-5 per cent, belong to the less valuable sub-bituminous class, which includes all the lignites and tertiary brown coals. In point of geographical distribution, no less than 69 per cent, of the total are located in America (almost wholly North America), 17-3 per cent, in Asia, 10-6 per cent, in Europe, 2-4 per cent, in Oceania, and only 0-8 per cent, in Africa. The distribution in the various countries of the world is as follows :—51-8 per cent, in the United States, 16-4 per cent, in Canada, 13-5 per cent, in China, 5-7 per cent, in Germany, 2-6 per cent, in Great Britain, 2-4 per cent, in Siberia, 2-2 per cent, in Australia, and 0-8 per cent, in Russia. China’s resources have probably been considerably under- estimated, and should perhaps be placed second to the United States; otherwise the relative positions of the remaining countries are probably substantially as stated. It is, therefore, probable that when Europe’s coal sup- plies arc approaching exhaustion, the world’s principal centres of manufacturing industry will be located in the two countries first named. The world’s demands for coal are increasing very rapidly year by year. Thus, in 1903, they were 800 million tons; five years later, that is, in .1908, they had increased to about 1,000 million tons; and by the year 1913 they amounted to no less than 1,250 million tons. This represents a continuous increase over a 10 years’ period at a “ compound interest ” rate of nearly 5 per cent, per annum, which rate is hardly likely to diminish after the conclusion of the present war. Inasmuch as the world’s demands have hitherto been principally supplied by three countries, namely, the United States, Great Britain, and Germany, which have raised practically 83 per cent, of the coal consumed in the world, attention may be concentrated on the statistics for these countries. If the average annual outputs for each, of the three successive quinquennial periods included in the 15 years between 1900 and 1914 be taken, the figures obtained indicate that the output of the United States is increasing annually at a “ compound interest ” rate ref 6 per cent.; that of Germany at a compound rate of 4 per cent.; whilst the British output is increasing at a compound rate of only 2 per cent. Assuming that these relative rates of increase are maintained, Germany’s out- put of coal will overtake that of Great Britain in about 20 years hence, when each country will be producing about 420 million tons per annum, and although Ger- many’s known reserves of coal are at present more than double ours, it may be doubted whether they will much outlast ours. The question of our coal export trade is one upon which much has been written from opposite standpoints: but without entering into any argument on these oppo- sing views, we may examine some of the leading facts * From a lecture (No. 2) at the Royal Institution of Great Britain. winch must be taken into account in formulating any opinion or decision upon the question. During the past 60 years our coal export trade lias . increased something like twenty-fold, both in quantity and value. Moreover, its value relative to other values exported has, during the same period, increased fourfold, until to-day it constitutes about 10 per cent, of our total exported. values. Thus, in the year 1913 we exported 97-7 million tons, or 34 per cent, of our total output, valued at 53 million pounds. Another feature of this trade is that, whereas both the United States and Germany export considerable quanti- ties of coal by land, their oversea exports are trifling compared with ours, and that in the year 1912 we actu- ally transacted over 70 per cent, of the whole seaborne coal trade of the world. Several factors have contributed to this astonishing result. One is the proximity of our finest steam coal seams to our ports, notably so in the South Wales coal field, which now exports more than 60 per cent, of its total output. Another is the increased demand for coal from Europe and South America; whilst a third factor has been the phenomenal growth of our mercan- tile marine, which for successful competition with foreign tonnage depends upon a good outward as well as inward cargoes. And inasmuch as the inward cargoes are chiefly foodstuffs and raw materials of considerable bulk in relation to their values, whilst our exports (except coal) are chiefly machinery and manufactured articles, whose bulk is small in relation to their value, our ship owners are in a position to offer low freights for outward coal cargoes. Hence maritime supremacy and a large coal export trade are interdependent, and it is difficult to see how ohe can be restricted without detriment to the other. Therefore, we must not expect any decline in our coal export trade, but rather the reverse, within the next half-century. Much has been written concerning the probable dura- tion of British coal supplies, and it has formed the subject of investigation by two Royal Commissions, ths first of which was appointed in consequence of the publication of the late Prof. Jevons’ great book on the coal question in 1865, and which reported in 1871, whilst the second issued its report as recently as 1905. Since that date, however, Dr. Strahan, the Director of the Geological Survey, has published, in the report of the International Geological Congress in 1913, ia revised estimate; and more recently still (1915) Prof. H. Stanley Jevons, following up his father’s work, has published another estimate, a remarkable book on the British coal trade. Tn making such an estimate it is necessary to consider two overruling factors, namely (1) the maximum depth at which it is practicable to conduct mining operations; and (2) the maximum thickness 'of seams which can be profitably worked. The first of those factors is deter- mined principally by the increase in temperature as we descend into the bowels of the earth. In this country the temperature at 50 ft. below the surface is constant all the year round at 50 degs. Fahr., and then it increases 1 deg. Fahr, for every 60ft. lower in depth. Both (loyal Commissions adopted 4,000 ft. as the maximum limit of practicable working, at which the temperature might be expected to be 116 degs. Fahr, (the deepest mine in Great Britain equals 3,500 ft., rind in Belgium equals 3,773ft.), and 1ft. as the minimum workable thickness of seam. The 1905 Royal Commission reported that our reserves of coal, within the said limits, then amounted to 141,635 million tons, but their estimate was certainly conservative, -and did not, for example, include the Kent coal field and other concealed measures. Dr. Strahan’s more recent estimate for the same limits, which included the Kent coal field and other items, was 178,727 million tons, whilst Prof. H. S. Jevons gives 197,000 million tons as a maximum quantity within 4,000 ft. of the surface. Adopting this as an outside estimate, and deducting 15,per cent, o i account of “ pit wastage ” (i.e., coal which is left fur one reatson or another in the workings), we obtain a net figure for actually available coal at the surface of, say, 168,000 million tons, or, say, about 580 times our present annual output. The serious aspect of the coal question for Great Britain is how long we can continue to get the available coal at a cos-t which will not place us as a nation at a disadvantage relative to our nearest competitors,* and from this point of view the achievement of all possible economies, not only in the getting, but also’ in the transporting and utilisation of coal, is of the greatest possible importance. In connection with the work of the Second Royal Commission on Coal Supplies, Mr. George Beilby pre- pared an estimate of the coal consumed in the United Kingdom for various purposes during the year 1903, when the total home consumption amounted to 167 million tons. Of this total, factories and mines accounted for 71 million tons (or, say, 43 per cent.); 28 million tons (or, say, 17 per cent.) were consumed in iron and steel works; another 15 million tons (or, say, 9 per cent.) were carbonised in gas works for the. manufac- ture of towns gas; railways accounted for 13 million tons (or, say, 8 per cent.); whilst 32 million tons (or, say, 20 per cent.) were used for domestic purposes; leaving only eight million tons (or, say, 3 per cent.) for all other purposes, including glass and pottery works, chemical works, and the like. Assuming this proportioned distribution to be still maintained, it follows that if the coal used in mines, factories, iron and steel works, and for domestic pur- poses, be lumped together, practically four-fifths of the total consumption will be accounted for; and it is also in these directions that there are the greatest margins for economy. The first point to be aimed at in all schemes of fuel economy is the abolition, whenever possible, of the * The average price of coal at the pit head increased durino- the period 1897-1910 by no less than 38 per cent.