October 1, 1915. THE COLLIERY GUARDIAN. 673 due rather to normal physiological processes than to any direct result of labour, and this is rendered more probable by the fact that the effect is continued throughout the Thursday and Friday during the manager’s absence, whereas in the other experiments the apparent development of fatigue at this time ceased to be obvious. The results from the fourth experiment (hearing) shows a great difference in the acuity of hearing of the examinees. In all of the examinees, whether with good hearing or with bad, the lessened acuity in the evening is remarkable. The results at the end of the series apparently again show in a remarkable manner the consequences of the absence of the manager of the works, with consequent relaxation in the supervision. Excretory System. On the supposition that breaking down of tissue is an essential factor in the production of fatigue, at all events so far as the muscular system is concerned, an enquiry into the nature of the products of degeneration which might appear in the urine could hardly be neglected. Accordingly, in 1913, Dr. Kent requested his assistant, Dr. By waters, to undertake an investigation on these lines. A long series of experiments has been carried out on these lines to determine the best conditions for the rapid and accurate estimation of small quantities of trimethylamine in the presence of ammonia, and an apparatus has been devised which seems to permit of its ready separation from the urine, and subsequent estimation. The amount of trimethy- lamine in normal urine and the various factors influencing it have yet to be determined. THE UNDERGROUND CONTOURS OF THE BARNSLEY SEAM.* By W. G. Fearnsidbs, M.A., F.G.S.f In this paper the author presented a preliminary account of the results of his statistical analysis of about a hundred records of borings and sinkings which have proved the depth of the Barnsley bed or its equivalents (the Cawthorpe, the Warren house coals of Yorkshire, and the Top Hard coal of Derbyshire) in Yorkshire. The majority of the records of borings and sinkings dis- cussed have been collected by a committee of the Midland Institute of Mining, Civil and Mechanical Engineers, and published by that institution in volume form in 1914, the sites at which the information was obtained being plotted on a |in. map. The depths to the coal have been corrected for the height of the sur- face location above sea-level, and, after the manner of Dr. Gibson’s map in the Geological Survey Memoir on the Concealed Coal Field, contour.lines have been drawn among the spot levels so obtained from the records of borings which have passed through permian strata show the character of the surface of the coal measures which underlie the carboniferous strata. In drawing the contour lines, no attempt has been made to distinguish between those changes of level in the seam between neighbouring pits which are due to faulting, and those due to the folding of the strata. Since, however, over most of the coal field the faults tend to nullify the change of level which the dip has accomplished, it is maintained by the author that to plot contours which show the average rate of change of level is a statistical process which can be demonstrated as approximating to truth. 1. From an analysis of the results as plotted, it appears that the underground contours in the Barnsley bed strike lines in Yorkshire in detail generally range either north-east to south-west or north-west to south- east, and that within the area under which the Barnsley bed has actually been proved by working, it is difficult to find either a north to south or an east to west strike constant over more than a very few miles of country. This circumstance, if general over the coal field, would seem to demand some revision of current views respect- ing the origin and structure of the Pennine chainif 2. The greatest structural division of the coal field “ basin ” is by the equivalent of a north-east to south- west anticline, of which the southern limb is along the line of the Don faults from Sheffield, by Rotherham and Conisborough, to Doncaster. North of this line there is some evidence for the existence of a syncline, with its axis central near Frickley. In ground from which the permian rocks have been denuded, the coal attains a depth exceeding 1,800 ft. below sea-level. The general line of this northern trough follows a north-west to south-east trend from Wakefield to South Kirkby, whence, displaced perhaps by the Don anticline, it bends somewhat through Bullcroft. South of the Don a wider trough, also trending north-west to south-east through Yorkshire Main Colliery (Edlington) and Bawtry, carries the Barnsley bed (at Rossington) below 2,600 ft. 3. The inclination of the Barnsley bed is at its steepest- near the outcrop, and after the manner of gentle folds, the measures flatten out when the centre line of the syncline is approached. There is no evidence to sug- gest any general eastward rise of the Barnsley seam within the area plotted on the map (the eastern boundary of the map is through Thorne and Retford). 4. By the plotting of the contour lines on Bartholo- mew’s larger coloured | in. contour map, the inter- * Abstract of paper presented to Section C (Geology) of the British Assoiciation. f Sorby Professor of Geology, University of Sheffield. J These views were admirably expressed by Prof. E. Hull, who, in advocating them in 1868, succinctly remarked (Quarterly Journal, Geological Survey, 1869, p. 331) :— “ Immediately upon the close of the carboniferous period, the northern limits of the Yorkshire and Lancashire coal fields were determined by the upheaval and denudation of the beds along east and west lines, while the coal fields themselves remained in their original continuity across the region now formed of the Pennine Hills from Skipton southwards, and that at the close of the permian period these coal fields were dissevered by the uprising of the area now formed of the Pennine Range by lines of upheaval ranging from north to south.” dependance of underground structure and topographical relief in the area of the exposed coal field has been well brought out. Over the whole coal field most of the ridges are of escarpment form, and are elongate along the line of strike, but from the map it becomes evident that wherever the strike of the Barnsley bed shows-a change of direction, there the escarpment ridges are found upstanding above their average height, and this whether they form the arches or lie in the troughs of the folds. From his experience of the application of the contour method to the study of the tectonics of the Barnsley bed, the author suggests that the method is of peculiar use- fulness in coal field work. He offered this preliminary account of the results of his work in Yorkshire, in the hope that workers on the western side of the Pennines might take up the method and use it in the further investigation of the many and difficult problems of geological saructure presented by the “ backbone of England.” COMPRESSED AIR FOR COAL- CUTTERS* By Sam Mayor. (Continued from page 623.) Compressed Air Coal Cutters. Obstacles to Efficiency.—Until users of compressed air coal cutters learn in what terms to demand efficiency, how to recognise it and appreciate its value, and main- tain it when they have got it, suppliers of the machines have little incentive to develop refinements, which are effective only when the machines are operated under the designed conditions. The operation of a coal cutter is involved in com- plexities from which stationary underground machinery is nearly or altogether free. The distinguishing features of coal cutters are as follow :— 1. They are used at places the most remote from the air compressors, and therefore receive air at lower pressure than other motors supplied from the same compressor. 2. Their position renders them specially liable to fluctuations of air pressure, due to varying losses in the pipe lines consequent upon the starting and stopping of other coal cutters or stationary motors, or of the overloading of the compressors. 3. The materials to be cut are often variable as to hardness, and at different parts of the same face the machine may be required to develop more or less power. 4. As portable machines, their rate of working is subject to the discretion or indiscretion of the operator, and the human factor is the most variable in the equation. 5. They work in confined space, among dirt, in com- parative darkness, in progressively changing position, or uneven floors, with unavoidable vibration, and under the control of a rough-handed class of men. 6. The conditions of service are unfavourable to maintenance of accurate adjustment of the parts. Coal Cutter Motors.—In the cylinders of coal cutter motors air cannot be expanded through a wide range as in the case of steam cylinders, because of the freezing troubles that attend expansion of the air. The valves of coal cutters must therefore cut off late, and the cylinders are nearly filled with air at initial pressure. At the end of the stroke the air, still retaining a consider- able proportion of the initial pressure, is exhausted, and its energy is dissipated in cooling the atmosphere. The higher the initial pressure is, the higher is the pressure of. the exhausted air, the greater is the proportion of rejected energy, and the lower is the efficiency of the machine. For this reason, a low air pressure is to be preferred on the ground of efficiency; but the lower the pressure, the larger and more expensive must be the transmission piping, and the larger and more cumber- some must be the cylinders of the coal cutter. Con- versely, sacrifice of efficiency in the coal cutter permits of the adoption of higher pressure and less costly pipe lines. The problem — in various phases familiar to colliery officials — is to make a just balance between capital expenditure and working cost, with in this case the additional factor of convenience in respect of dimen- sions of piping and of the machine. In this country the general practice is to adopt a pressure at the surface between 50 and 801b. per sq. in. It is sometimes specified that a coal cutter shall work at, say, 301b., and shall be capable of withstanding a working pressure of 60 to 701b. Such stipulations impose upon the machine undue concessions to improper conditions of power supply, and they are not only incom- patible with reasonable efficiency, but also involve mechanical difficulties. The moving parts and bearing surfaces of the air motor are proportioned to the power required to be delivered at the designed speed to the cutting member of the machine; if the cylinders are of sufficient size to develop the required power at 301b. pressure, it is clear that they will give much higher power at 601b. pressure, and the machine may be over- loaded, or its motor may race to a dangerous speed. These tendencies may be checked by wire drawing the air at the throttle valve, but the average machineman does.not concern himself with niceties of adjustment, and is careless of the consequences to the machine of wide fluctuations of pressure. On the other hand, if a pressure of, say, 401b. at the machine is promised, and the cylinders are proportioned to develop economically the required power at that pressure, these cylinders are too small to enable the machine to work satisfactorily at 20 or 251b. Makers of machines know that they cannot rely upon promises * From a' paper read before the Institution of Mining Engineers. of pressure, and therefore at sacrifice of efficiency in use of air they must provide cylinders of ample size to allow for reduction of pressure. Moreover, they know that economical use of air at the designed pressure will not have recognition, whereas they will probably have credit if the machine works satisfactorily at pressure much below the promised value, and certainly much blame if 0 O*l 02, 0 3 04 OS 0 6 0 7 0 8_______________________________09 IO 1300 1400 422. 600 200 ±od St| Yawps Pw Min A- Cubic Feet of Fhee Air Jseo Per Min CoMPwtssEQ Air Cum Gutter;. Kouns in <=ree Coal4 3 Undercut B- Cubic Feet of Frze Air Pen Minute Sq Unoekcut Air Pressure at machine 40 toggles Per tf ___________________________- _ _ - _ _ , _ ______________ ..______________________l g l-S f-4 > 5 g-S S O 7-5 to ft S IS 17 5______________________________32 5 2,5 2.7-5 30 32.-5 35 37 5 Linear inches Pzr Minute Rate of Cutting Fig. 13.—Air-Consumption against Cutting Speed. it does not so work. If the machine cuts satisfactorily, no inconvenient questions as to efficiency arise. An example will illustrate the difficulty. Relation of Air Consumption to Cutting Speed.—The curves in fig. 13 illustrate the importance of driving a compressed air coal cutter at the highest travelling speed of which it is capable. The curve A is plotted from meter tests of a machine in operation, and curve B is deduced from A. Every machine will have its own characteristic curves, the exact form of which will depend upon the design of the machine and on the point of cut-off of its valves, but the curves given are fairly representative. In order to drive the machine unloaded, 76 per cent, of the air absorbed at full load is required. The volume of air used thus depends much less upon the distance travelled by the machine than upon the number of revolutions of the air motor, and the rate of advance is, of course, variable at will, independently of the speed of the air motor. The practical lessons of these curves are as follow :— 1. The driver should not allow the air motor to run at a higher rate of revolutions than is necessary to develop sufficient power to maintain any given cutting speed. To allow the engines to race not only risks mechanical damage to the machine, but involves excessive extravagance of air. 2. The cutter picks of the machine should be kept in proper adjustment, so that the fastest cutting speed may be obtained, and should be renewed when they are so blunted that the rate of travel of the machine is materially reduced. 3. The face should be so prepared and the timber so set prior to the cutting shift that the machine shall not be subjected to difficulties. Where bends occur in the face, the speed of travel is reduced to enable the machine to negotiate them : or, where projecting coal is left by the strippers, or where props are set too close to the face, the machinemen while attending to such matters reduce or stop the haulage feed, while the air motor continues to run, and to use nearly as much air as it would at full power. Avoidable inter- ruptions to the steady progress of the machine there- fore result, not only in reduced distance cut per shift, but in much higher expenditure of power for the distance cut. The curves also suggest that the haulage feed of com- pressed air coal cutters should be adjustable in small stages, so that an intelligent driver may be enabled to take the best out of the machine under the varying conditions of service; the very low efficiency at light loads renders this much more important than in the case of electrically-driven machines, in which the consump- tion of power is more nearly proportional to the work performed. Maintenance.—The air consumption is affected by the condition of the mechanical parts of the machine gener- ally, but the parts which are of chief concern in this connection are the valves and pistons of the air motor. In practice the open end of the hose when detached should be protected by a plug to exclude dirt, or the hose before being connected should have the dirt blown out of it by air. Pistons and piston rings and cylinders worn oval are also common defects that result in high consumption of air. Many machines are working to-day in which, after many years of service, the valves and sea tings, pistons and cylinders, are so worn that the normal air consump- tion per square yard cut is doubled or trebled; but so long as the air supply i s maintained, and so long as the machine continues to undercut a distance considered satisfactory, no question of overhaul arises. It is worth noting that an effect which quickly fol- lowed the purchase of compressed air by meter at the Rand mines was the adoption by the mine owners of a rigid system of periodic withdrawal of the rock drills for overhaul; to this system the reduction of air power used per drill was chiefly due. The withdrawal to the surface of a longwall coal cutter is a much more serious matter, and a system of periodic withdrawal is not to be lightly imposed. But at least a definite system of periodic test by meter of the air consumption of each machine should be adopted, and, when such tests render it necessary, the machine should be withdrawn for overhaul, and should pass a satisfactory air consumption test before being again sent underground.