December 4, 1914. THE COLLIERY GUARDIAN 1181 THE CASE FOR THE ELECTRIC LAMP.* By William Maurice, F.G.S. It is permissible to doubt whether the necessity for revising our views on underground lighting has even yet met with adequate recognition. A considerable extension in the use of electric lamps has lately taken place, but it is suspected that this extension is more closely due to pressure from without than to recogni- tion from within. And yet there is surely better justification for installing electric lamps than the plea of Home Office pressure. Inspectors of mines do not, of course, “ order ” electric lamps to be used, but it is known that they favour development in this direction. Why, however, should any pressure be necessary So relatively long ago as May .1911 the writer endeavoured to show that consideration of the question at issue was overdue.-}- In his opinion there is no known invention which is likely to have so beneficial an influence on labour conditions, no invention which is so clearly destined to improve the miner’s lot, no invention that gives such bright promise of reducing the risks of under- ground work to anything like the same extent, as the portable electric lamp. He is of opinion that the oil lamp has had its day. The illumination which it pro- vides is not very notably better now than that which was obtainable 30 years ago. In fact, on the whole, it may be doubted whether the available illumination is now so good as it was, for the compulsory employment of double gauzes, or their equivalent, and the (not legally, but more or less practically) compulsory addi- tion of a fifth pillar to the glass containing cage, both make for impaired illumination. The flame safety lamp burning benzine, which was invented by Mr. Chas. Wolf in the year 1883, constitutes, the writer believes, the only notable improvement in lighting that the mining world at large has accepted as such since the flame of a safety lamp was first surrounded by a cylinder of glass. After all, light is what a lamp is provided for. Any other property that a flame safety lamp may possess should be recognised as subsidiary to its main purpose, which, again, the writer submits, is to give light. The writer makes no excuse for setting forth, as he has done many times before, the three basic conditions for safety as space, order, and light. Of these, the first—space— is limited by natural conditions; the second—order—has received extensive expression in revised legislation and better management; while the third—light—remains relatively untouched. True, this, the only really basic condition that remained to be attacked, found recogni- tion in the enactments to which reference has been made; but has it yet been recognised by the mining industry as the ground work of a justifiable policy? To-day the cry for “ more light ” is being perr.istentlv urged by the leaders in every walk of life, and the present violent disturbance to the world’s thought will but serve to clarify and to intensify this demand. In the mine “ more light ” seems to the writer to offer the easiest possible solution of many problems that have hitherto been regarded as either technically or commer- cially insoluble. More light in the mine means— (1) Cleaner coal. (2) Increased output per man, whether engaged in stall- or road-work. (3) Less time lost in starting work. (4) Less time lost in re-lighting lamps. (5) More effective supervision. (6) Enormously diminished risk of firedamp explo- sions and underground fires. (7) Fewer accidents from falls of roof and side. (8) Fewer haulage accidents. (9) Fewer miscellaneous accidents. (10) Reduction in the number of cases and probably a complete elimination of miners’ nystagmus. (11) Reduced cost of insurance and compensation for injuries. (12) More agreeable conditions of labour. That there will be less excuse for filling stone and dirt with coal when the light is good must be self-evident, and it is already known to mine managers that some improvement has actually been obtained. It has also been recognised that miners can and do fill more coal, and do more yardage on straight work, when using electric lamps. They have, moreover, been the first to admit that they have done more work with no per- ceptible extra effort. With regard to working time lost, it is perhaps not sufficiently recognised that the loss of even a minute or two per man per shift may amount in the aggregate to something important. When using oil lamps every man must wait a while, or at least go slowly imme- diately after he descends the mine, in order that his eyes may adjust themselves to the change from light to darkness. In practice there is probably a loss of time of at least 15. minutes between getting down the pit and starting into the workings. Every minute may become 1,000 minutes, amounting to, say, 16 hours, which is two men’s shifts, and has a value of, say, 15s., in a pit employing 1,000 men. In a five-shift working week the value of a loss of one minute per man per shift is thus £3 15s., which is probably sufficient to pay for the extra cost of maintenance of electric lamps. Then there is quite a serious loss of time in sending workmen to lamp stations to get their lamps re-lighted when these have from one cause or another gone out. If it be said that 10 per cent, of the flame safety lamps used underground get “ in the dark ” each shift—and the writer believes that the official statistics record a higher percentage than this—the number of hours of * From a paper read before the Midland Institute of Mining, Civil and Mechanical Engineers. t “ Electric Hand Lamps for Collieries,’’ by Wm. Maurice, The Electrician, second mining issue, May 12, working time lost per day must be considerable. “ Time is money ’’ both to the coal owner and to the miner. Every stallman who loses a minute loses a farthing!* That more effective supervision is possible with better light is a statement that hardly needs any argument. With regard to the contention that the substitution of electric for flame safety lamps will diminish the risk of firedamp explosions, so far as the writer’s personal opinion may carry weight, it is based upon more than 24 years’ experience of miners’ lamps, both flame safety and electric, some 15 years of which were devoted to active colliery management. Without begging the question, and without attaching too much importance to official reports, there is ample genuine legal evidence that flame safety lamps may be a source of danger in the mine. Nothing can alter the fact that a “ safety lamp,” as ordinarily understood, is only a more or less carefully shielded naked flame. Workmen have been known to boast that there was no safety lamp which they could not open if they were so minded, and in any case a broken glass, a blow from a pick, or even the omission of a washer, may convert a flame lamp into a direct source of danger. Over and above all, there is the fact that the light given by even the best safety lamp is quite inadequate as a means of protection from dangers other than gas. The danger f ^m falls of roof has taken a greater toll of lives than that from explo- sions; and therefore the greatest contributory agent to general safety is “ more light.” That more effective lighting will diminish the inci- dence of nystagmus is now beyond question. It is, however, necessary to say that those who instal electric lamps for the special purpose of eliminating nystagmus and look for immediate results are likely to be dis- appointed. The expected improvement will undoubt- edly come, but the rate of improvement will depend upon the nature and long standing of the cases, and on the proportion of latent tendencies in individual cases among those employed in the mine. A really reliable opinion on the effect of . improved lighting conditions on nystagmus cannot be expected in less than three years. In this connection discrimination should be exercised between the photometric value. of light and its useful effect in the places where it is to be employed. Every* one familiar with laboratory practice knows that a photometer can within certain limits be so manipulated as to give the desired result, and it therefore goes with- out saying that comparisons of photometric tests are liable to be misleading. Apart from this, the photo- metric value of a given light is not necessarily an indication of its practical usefulness. Flame lamps will give more or less constant values under similar conditions, but no one is competent to speak of the illuminating value of an electric lamp unless he is possessed of certain special electrotechnical knowledge. There are so many pitfalls that, while an observer may record with approximate accuracy the photometric value of a given electric lamp, he is merely recording results that he obtained under a series of (probably) insuffi- ciently specified conditions. The same remarks apply to statements as to the duration of the standard light. The condition of the electrodes in a cell, the particular point in the life of the cell at which the test was made, the density of the electrolyte, the rate of charge, the condition (as to cleanliness, etc.) of the contacts, the make and quality of the metallic filament lamp bulb, the number of hours that it has previously “ burned,” the quality and condition of the outer glass, and many other points, have all an important bearing on the photo- metric value of an electric lamp and the duration of its light. Only an average of many tests taken throughout the working life of a lamp would give reliable data, and even then the data would not necessarily indicate what the lamp could do, but what it had done. It might be thought that this was a “ distinction without a differ- ence.” The writer’s reason for making the distinction is that many electric lamp installations are both costing more to maintain and giving much less satisfactory ser- vice than they would if only they were cared for in a reasonably intelligent fashion. A great deal more lies in the proper management of electric lamp cabins than appears to be generally sup- posed. It was commonly said not many years ago that a coal owner would expend many thousands of pounds on electric plant, and then put a wooden-legged labourer in charge of it. The criticism was essentially tiue. Many thousands of pounds have been spent by coal owners on repairs and renewals to electric plant which would never have been required if competent men had been placed in charge. It has taken an Act of Par- liament to effect a change that ought to have been dictated by common sense. Is history repeating itself? Thousands of pounds are now being spent in providing electric lamps, and is it not a fact that the lamp room has been generally manned by the maimed and decrepit soldiers of the mining army? Is it not a fact that many such individuals or men of similarly inadequate capacity are now being employed in electric lamp rooms —put in charge, that is, of a department which to be successful demands at least alert intelligence and a reasonable degree of electrotechnical expe’ience? A well-organised electric lamp cabin is in itself still some- what of a novelty. The successful management of one calls for a higher degree of intelligence than has hitherto been considered necessary. The provision of that higher degree of intelligence makes all the difference between success and failure; the omission of it is misplaced and most costly economy. The elimination of nystagmus, the reduction of other insurance and compensation charges, the improved quality and quantity of output, the increased efficiency of the workers, and, not least, the greater comfort with which men work when using electric lamps, must all tell in favour of this undoubted underground revolution * If a stallman’s earnings be 10s. per day, then 10s. =480 farthings; and eight hours = 480 minutes. —a revolution which (it is the writer’s profound belief) is destined to affect radically the practice of, mining, which will promote safety and efficiency in directions that are here only remotely indicated, if at all, and which will be so beneficent alike to owners and to mine workers that the mining engineers of the future will marvel if it should appear that, like the British Empire, “ it came about during a fit of absence of mind.” CABLES.* By C. J. Beaver. (Continued from page 1132.J Vulcanised Bitumen Cables. The general idea of the physical properties of vul- canised bitumen that the average user of vulcanised bitumen cables probably has in mind is a general simi- larity to rubber, without any very specific appreciation of the limitations of that resemblance. It is very desirable from both maker’s and user’s points of view that such general ideas should be ventilated. To regard the matter first in a broad way, it may be said that the cohesion between the particles of material is much less in vulcanised bitumen than in rubber. This means that such properties as resilience, elasticity, and resistance to tension, compression, and other mechanical strains have considerably lower values in vulcanised bitumen than in rubber. The variation in consistency with a change of temperature has probably the most direct bearing on the subject from the cable user’s point of view. At very low temperatures (around or below the freezing point of water) it tends to yield to sudden shock in a brittle fashion, breaking up with a conchoidal fracture. At medium temperatures up to, say, lOOdegs. Fahr., it is a toughly plastic body having considerable resilience and resistance to mechanical stress. At temperatures in the neighbourhood of 100 degs. Fahr, to 130 degs. Fahr, it begins to lose its toughness, and at still higher temperatures its cohesion disappears to a considerable extent, although its resilience appears to be increased. As a result of this its manner of yielding to mechani- cal forces at very high temperatures bears a general resemblance to that of gelatinous materials, and has no parallel in the behaviour of rubber. It does not yield by softening or by any process resembling the melting of bituminous, waxy, or resinous substances. A material, intermediate as regards softness or hardness, possessing maximum toughness at medium tempera- tures, wide limits of temperature range, and approxi- mately equal resistance to all kinds of stress at a low temperature, is obviously the most desirable. To pass from the physical properties of the material itself to the effect of the limitations thereof on cable manufacture, it goes without saying that a great deal of work has had to be done since the early days of its introduction, first on the raw materials, secondly in the development of manipulation processes and the details of application, and thirdly in connection with the assembly of component parts of cables in such manner as to supplement the physical limitations above- mentioned. The two first-mentioned points are rather beyond the scope of this paper; the third is shown by the commer- cial success of well-known types of vulcanised bitumen cable largely used under very arduous conditions, such as those which obtain in mining work. Twin and three- core vulcanised bitumen cables are more largely used under such arduous conditions than other types, and the fact that such cables are made without internal reinforcement by any other material, gives a good idea of the result of close attention to suitable assembly. With regard to chemical properties, the stability of vulcanised bitumen is remarkable. Unlike rubber, it is not appreciably subject to natural deterioration under normal conditions of atmosphere and temperature, and it may therefore be regarded as comparable with paper insulation in that causes of deterioration are practically always extraneous causes. So far as direct chemical attacks which may be encountered in practice are con- cerned, the material is exceptionally inert to the action of substances of an acid character. As might be expected from the fact that vulcanised fatty pitches, i.e., saponifiable substances, largely enter into the composition of vulcanised bitumen, it is much more susceptible to the action of alkaline substances. The direct action of such substances is usually, however, only superficial (to a greater or less extent, depending on the degree of free alkalinity), and it is a fact that even such severe conditions as continual exposure to coal pit waters—which are usually of an alkaline char- acter—have had no appreciable effect on vulcanised bitumen. Even if such waters contain free alkali equi- valent to 25-30 grains per gallon (estimated as sodium carbonate), which is considerably above the average for waters encountered in coal mines in this country, and the vulcanised bitumen is freely exposed to their attack for two or three years, the depth of penetration of the action is inappreciable. Waters of a brackish char- acter which sometimes occur in coal mines near the sea and elsewhere, and which may contain 1,000-1,300 grains per gallon of the chlorides of sodium and magnesium, have no action on vulcanised bitumen. Although not coming strictly under the category of chemical deterioration, it may be permissible for the author to digress for a moment to correct the fallacious impression which exists in some quarters, and which has recently been perpetuated in a Board of Trade report,! that vulcanised bitumen is softened by contact with coal gas. The statement is correct for natural bitumen, pitches, etc., but is decidedly incorrect for vulcanised bitumen. * From a paper read before the Institution of Electrical Engineers. f Report of Board of Trade Committee on Electric Mains Explosions, p. 4, 1914.