December 10, 1915. THE COLLIERY GUARDIAN. 1191 The question of fuel economy is Fuel Economy never worn out, and is always in Power interesting both to the practical Supplies. and theoretical man. We are glad, therefore, to refer to the views upon this subject of Mr. C. P. Sparks, who made it a feature of his presidential address recently delivered before the Institution of Electrical Engi- neers. As an example of short-sighted policy by our legislators, Mr. Sparks showed that the electric lighting and power industry has been stifled by the restrictions imposed by the Electric Lighting Act of 1882 and subsequent legislation, the effect of which has been to create a number of small areas instead of a few large ones. Thus in the London area there are no less than 28 separate electric supply under- takings and 10 separate traction supply schemes. This arrangement necessitates 38 power stations, many of which have to rely upon cooling towers for their condensing water, with a resulting loss of efficiency which has been represented as an additional cost of £14,000 per annum for a 90,000 kw. station, even with cheap coal at about 9s. per ton. It would be fairly easy upon such a basis to calculate the total cost to London alone, at the present price of coal, of a policy conceived in complete ignorance of elementary engineering economics. Mr. Charles Merz a few years ago nearly succeeded in carrying through Parliament a Bill, the object of which was to reduce these separate power stations to three main sources of supply. The subject is bound to come up again if only on account of the waste and extravagance of the present arrangement, which will continually become more pronounced as the cost of fuel increases. Mr Sparks showed that the saving in fuel effected by a centralised supply is due partly to the reduction of stand-by losses and partly to the higher efficiency of large generators and boiler plant when worked under skilled supervision. He places the actual saving in a central scheme, as compared with isolated plants, at not less than 75 per cent., an amount which seems to be rather high, but quite conceivably correct when all the factors are taken into account. Economy in fuel is not, however, confined to centralisation of supply alone. There is a growing tendency, even in isolated stations, to effect improve- ments in steam-raising efficiency. For example, the universal use of large boilers of the water-tube type, combined with superheaters and mechanical stokers, enables small coal of medium calorific value to be employed with greater economy than was possible with smaller, hand-fired units. Thus the average efficiency in conversion of the heat energy of the coal has been raised from about 50 to 75 per cent, under ordinary working conditions. The use of small coal also enables other economies to be effected, and we can perhaps look forward to the time when boilers will all be gas-fired, the gas being obtained from low-temperature producers with recovery of by- products. Another matter touched upon in this address concerns the future of coal for lighting and heating purposes. We cannot now embark upon a critical comparison of the relative advantages of electricity and coal gas for lighting purposes. We merely cjuote Mr. Sparks’ figures, which show that a ton of coal converted to electricity in a modern power house can furnish no less than 750,000 candle power hours, as compared with 260,000 in the case of gas, assuming 13,000 cubic feet of gas per ton of coal. There would appear to be, on the strength of these figures, a saving in coal of nearly two-thirds; but possibly the gas engineer would have something to say upon that. With regard to heating, we can certainly believe that gas still holds the field in regard to economy. Mr. Sparks says that with the present method of conversion of the heat energy of coal into electricity it is only possible to deliver to consumers about 15 per cent, of the heat energy of the fuel. In the case of gas we believe about 18 per cent, of the heating value of the coal is available in the form of gas, and 58 per cent, in the coke. Thus, although the consumer receives only about the same proportion of the total heat energy of coal, whether he uses gas or electricity, gas is cheaper under modern conditions of conversion. There is running through this very practical address an undercurrent of thought which coal producers should certainly keep in view. Cheap coal has hitherto been a distinct disadvantage to engineering advance, because the engineer aims at efficiency in conversion of energy, and this is not always synony- mous with reduction in fuel costs. Our abundant coal supplies have contributed to wasteful methods, but the time has already arrived when the question of fuel economy is becoming more and more urgent to the power user, and the engineer is even now engaged in fighting the upward tendency in the cost of coal by curtailing the demand—that is to say, by getting more out of it. The Seventh Report of the Explo- Explosions sions in Mines Committee is made in Mines up of two distinct parts. In the Committee : first place, there is a statement by Seventh Prof. H. B. Dixon qualifying his Report. adhesion to the Sixth Report, the draft of which he had been unable to see owing to his absence from England. Prof. Dixon takes exception to the statement that “The 1 : 1 mixture of coal dust and incombustible dust can, we believe, be regarded as proof against ignition by the flame of the most violent firedamp explosion.” His reasons for dissent from that very definite statement are perhaps more logical than practical, and, as a man of scientific training and habit of mind, his caution against too sweeping a generalisation can be understood. Precisely how much evidence is necessary to establish an inductive proposition must depend upon the circumstances of each case. We have never believed that the Eskmeals tests have yet done more than to establish a strong probability that the stone-dusting method, as described above, will be capable of checking the extension of any firedamp explosion likely to take place in a coal mine. The real difficulty in any actual occurrence would be to prove that the con- ditions had been properly fulfilled. The second and longest part of this report con- tains the results of Dr. J. S. Haldane’s investiga- tions into the hygienic effects of stone-dusting. Much of this is a recapitulation of statistical know- ledge already available, together with a review of the well-known experimental work carried out by Prof. Beattie at Liverpool University, by Messrs. Winmill and Graham at the Doncaster Coal Owners’ Research Laboratory, and, many years ago, by Prof. Arnold at Heidelberg. The more original part of Dr. Haldane’s report is the account given of some recent experiments, carried out by himself and Mr. Mavrogordato, undertaken primarily on behalf of the Medical Research Committee under the National Insurance Act. As the details of these new researches are given in full in another column, it is only necessary here to call attention to some of the more important deductions that can be drawn from them. In the first place—and this, in our view, is by far the most important point in the report—it must be stated that Dr. Haldane’s conclusions do not appear to be any too optimistic. In a general sense, he finds that coal-measure shales which are free from grit may be regarded as relatively innocuous when breathed in the form of fine powder, but even these dusts, as well as coal dust, he thinks may prove harmful in the long run. Then, again, he places the colliery manager in a dilemma by insisting in one part of the report on the necessity for grinding the shale to a fine powder, while, in another part, he states that it is not desirable to grind it too fine. The reason for this precaution is the danger of crushing the grains of silica, which all shale dusts contain, to a greater or less degree. In their natural state these silica grains are comparatively, if not absolutely, harmless, because they have no sharp edges. The original angularity of the grains has either been worn down by attrition in carboniferous waters, or it has been covered by a colloidal deposit of secondary silica. The precise cause of the physical state of these silica grains does not appear to be material, but it is obvious that, if crushed, they may lose their exceptional qualities, whatever these may be. The colliery manager, however, needs practical guidance, and to be told to grind his shale to a fine powder, but not too fine, is not sufficiently explicit. If we may be allowed to offer any suggestions, and we do so with every desire to assist in this difficult investigation, we think that useful results might follow from the adoption of Dr. Moir’s methods in regard to these shale dusts. Dr. Moir, working on behalf of the South African Committee on Miners’ Phthisis, paid particular attention to the size and shape of silica particles in stone dust. His method was to collect this dust on sugar solutions and examine them microscopically. In the Oxford experiments some difficulty seems to have been experienced in the determination of minute frag- ments of quartz, and their differentiation from other particles, such as sericite, chlorite, rutile, anatase, etc. Perhaps these difficulties would be overcome by the elegant methods recently advocated by Mr. Allan Dick, who, by using dark field illumination and media of different refractive indices, was able to separate the constituent particles in a mere smudge of clay on a glass slip. What is needed now is a definite research on finely-ground shale, and a determination of the permissible limits to which the grinding may be carried without sacrificing those qualities upon which immunity from harmful effects apparently depends. Another possible! line of investigation was indicated in the recent Milroy lectures delivered by Dr. Collis of the Home Office. He there showed how incipient lung trouble in miners can be detected long before actual disease becomes manifest, by the use of X-rays. The lungs of miners affected by incipient silicosis show distinct shadows in their radiographs. Much has been made of the fact that miners working in pits where stone dusting is systematically carried out have so far shown no apparent tendency to disease arising therefrom. But silicosis is an insidious and cumulative condition. The argument would be greatly strengthened by an X-ray exami- nation of these men. If the lungs should prove to be absolutely free from shadows we could then, perhaps, feel full confidence in the harmlessness of these shale dusts. In this connection, attention may be drawn to the radiograms obtained by Dr. Barwise of perfectly healthy lungs in the case of workers in Derbyshire limestone. Prof. Beattie’s experiments seemed to indicate that even limestone dust is dangerous, and this apparent discrepancy also needs some further explanation. Turning now to flue dust, which is placed by Dr. Haldane on the list of possibly dangerous materials, the great value of these investigations is clearly illustrated, for on its merits flue dust appears to be peculiarly suitable for rendering coal dust inexplo- sive. The precise mineral composition of flue dust has not been clearly established, although fused silicate may, as Dr. Haldane suggests, be its chief constituent. The Oxford experiments showed, how- ever, that the lungs do not readily free themselves from flue dust, and as its inhalation is exceedingly unpleasant and it is irritating to the eyes, it is clearly better to adopt Dr. Haldane’s advice to abandon its use. Dr. Haldane gives some very clear indications of the kind of shale dust most suitable for use in mines. These form a particularly useful part of the report, for it cannot safely be taken for granted that all shale dusts are equally satisfactory. In fact, it is difficult to avoid the impression that Dr. Haldane is not himself convinced that the extensive adoption of stone dusting in mines may not lead ultimately to undesirable physiological effects from the point of view of the miner’s health, for he is emphatic in his advice to reduce as far as practicable the inhalation of any dust whatever. Dr. Haldane has made a very valuable contribu- tion to the stone dust problem. It is evident that progress is being made in the desired direction, but the end is not yet. We cannot resist the conclusion that this Seventh Report of the Explosions in Mines Committee will be regarded as a slight check, perhaps opportune, upon the prevailing tendency to believe that the great coal dust research cannot be further extended with any advantage. It would be safer to conclude that the truth is only beginning to emerge.