February 11, 1913. THE COLLIERY GUARDIAN. 335 vice-president of the institute, was contributed by Mr. R. W. Berkley, and a similar document with reference to the late Mr. Thomas Walter Benson, a former presi- dent of the institute, was contributed by Mr. W. J. Benson. The “ Bohres,” “ Oldham,” and “ Tharos ” miners’ electric safety lamps were exhibited and described. The meeting then ended. Height of Flame and Cap before the “Gathering.” Per- centage of coal gas. 0 2 4 6 ! 8 10 12 14 1 18 20 22 24 26 28 30 y Pressure in (inches of water. 7 7’50 7*47 7*42 7*36 ■ 7*25 7*07 6*89 6*65 6*41 ! 6*09 5*75 5*41 5*07 4*70 ! 4*32 3*92 / Height of fl R.Tn e 6f 6*77 6*79 6*72 6*68 ; 6*60 6*49 6*37 6’23 6*07 ; 5*87 5*60 5*30 4*98 4*55 ! 4*10 ! 3*57 C QTlH PAiD 6’04 6*03 6*02 j 6*00 5*96 5’91 6*86 5*80 5*73 5*61 5’45 5*19 4*90 4 39 : 3*88 ' 3’22 t 6VULVI. • MINING INSTITUTE OF SCOTLAND. A general meeting of the Mining Institute of Scotland was held on Saturday last in the Heriot-Watt College, Edinburgh, Mr. James Hamilton, president, Glasgow, in the chair. The attendance of members was representative. At the outset, the following gentlemen were admitted to membership:—Messrs. John Duff, manager, Birsieknowe Pit, Beith, Ayrshire; Jeremiah Heron, under-manager, Cowie, Stirlingshire; Donald McBride, manager, Coursington Colliery, Motherwell; Andrew Russell, colliery manager, Bengal, India; John H. Anderson, resident engineer, Steamship Owners’ Coal Association, Essex; John S. Allan, agent? Balgonie Colliery, Markinch; John Wilson, assistant consulting engineer, Airdrie; and R. R. Johnson, mine surveyor, Lochgelly, Fife. Owing to the absence, through illness, of Mr. James Barrowman, Hamilton, Prof. Latham, Glasgow University, officiated as secretary at the meeting. Proposed New Rules. The President gave notice of motion in regard to certain alterations which it was proposed to make in the rules of the institute. It was explained that, con- sequent on the forthcoming retirement of Mr. James Barrowman from the secretaryship, an alteration was contemplated in the rules to permit of the offices of secretary and treasurer being combined in one person, the honorarium attached to the same being £100 a year. Improvements Relating to the Anemometer and Hygrometer. Mr. Henry Briggs, Heriot-Watt College, Edinburgh, thereafter read a paper on “ Improvements Relating to the Anemometer and Hygrometer.” In the first place he described a weighted-lever attach- ment for anemometers which is being manufactured by Messrs. John Davis and Son (Derby) Limited, and an illustration of which has already appeared in the Colliery Guardian (Nov. 22, 1912). He next referred to the “ Hygrograph,” this being a chart for reducing the readings of a wet-and-dry-bulb hygrometer. The chart has been constructed from Glaisher’s “Hygrometrical Tables.” The readings of the two thermometers having first been taken, the positions corresponding to the two readings are noted on the scale running up the right hand side of the chart. An inclined line indicating the wet-bulb reading is then followed until it meets the horizontal line indicating the dry-bulb reading. Then, by aid of vertical lines, the point of intersection is referred to a scale labelled “ Percentage saturation ” on the bottom or top of the chart. In this way the relative humidity is ascertained by inspection. The range of temperature (dry-bulb) is from 35 degs. to 105 degs. Fahr., and the range of relative humidity from 100 to 50 per cent. It is believed that the con- ditions as to temperature and humidity generally met with in British mines are covered by the chart. A second form of hygrograph has been designed for countries hotter and drier than our own; it includes higher temperatures and degrees of humidity down to 20 per cent. The “ Hygrograph ” may be obtained, engraved on aluminium or on silvered brass, either attached by screws to the face of an ordinary hygrometer, or separately, in a thin leather case. A discussion took place and was adjourned till next meeting. Atmospheric Pressure and Gas Caps. Mr. C. J. Wilson, Heriot-Watt College, Edinburgh, followed with a paper entitled, “ An Investigation into the Influence of Variations of Atmospheric Pressure on Gas Caps.” He recalled that at the annual meeting of the Institute, held in Glasgow, in April 1912, he had communicated the results of some experiments, which seemed to show that an increase of atmospheric pressure caused a decrease in the height of the gas cap. Redeeming a promise then given, he now put forward the results of a further set of tests, which fully confirmed his original conclusions. One result had been to show that the effect of volume of feed was of great importance. If the nature of apparatus available, or if the intention or inattention of the manipulator gave a different volume of feed at different times, the caps produced by the particular percentage dealt Height of Flame and Cap, in Inches. itage I gas. 0 i 2 4 6 8 10 12 14 1 16 18 20 22 24 26 28 30 O < In. of g ® S ( water, f » g-S and cap, in inches. 41 3’19 3’04 2’89 2*74 2*59 2’45 , 2’29 2*14 2’00 1’85 1’70 1*54 1’39 1’24 — — 4 2*69 2’57 2’45 2’33 2*22 2*09 1’97 1’85 1’73 1’60 1’48 T36 1’24 1’12 — — 2’35 2’25 2’15 2*05 1’96 1’87 1’78 1’68 1’58 1’49 1’40 1’30 1’20 1*10 — — 31 2*17 2’09 2’00 1*92 1*83 1’74 1’67 1’58 1’49 1’40 1’32 1’25 1’16 1*07 — — 3f 2*06 1’98 1*90 1’82 1*75 1’68 1’59 1’52 1’45 1’38 1’29 1*21 1’15 1’06 — — 3 1*97 1’89 1’82 1*75 1’68 1’62 1’55 1’48 1’41 1’34 1’27 1’20 1’13 1’05 — — 2f 1*89 1’82 1’75 1’68 1*62 1’56 1’50 1’44 1’38 1’31 1’24 1’18 1’11 1’04 — — 21 1*85 1’78 1’71 1*64 1’58 1’52 i 1’46 1’40 1’34 1’28 1’22 1’16 1*09 1’03 — — 1 with, say for the instruction of firemen, would bear no relation to the caps given under natural conditions. Any safety lamp used for instruction in gas testing must have just that of volume air feed which it naturally required. The lamp must either be so constructed that it was impossible to vary the volume of air reaching the flame, or else the apparatus used must be absolutely self-contained, must in its ultimate action be independent of any increase or decrease of pressure in the pipes supplying it with air, gas or water. The size of the cap decreases with increasing pressure, whatever the sustained volume of feed; and though volume of feed increases the size of the cap, increase of pressure still causes the cap to be smaller unless the variations in volume of feed are excessive. After all the experiments were finished, the data obtained in this manner were plotted to scale along with the calcu- lated mean values. From them the mean value was drawn in for every 2 in. of pressure; the different points being connected, the lines for percentages at varying pressures were drawn. First the lines of equal pressure for different percentages were plotted from those first rough curves- By comparing the one set with the other and following up the reason of every irregularity in either, it became possible to eliminate practically all the errors in the lines originally plotted, and to fix on what appeared to be the correct pressure lines. From these the percentage lines were plotted anew ; as a great surprise they came out as perfectly straight lines. Not only that, but they were found to agree remarkably closely with the mean values originally calcu- lated. In many cases there was absolute agreement. In almost no case is the difference in the height of the cap so great that it could be appreciated in practical work. These results were finally gathered into a tabulated list giving the height of the cap of each percentage at every 2 in. of pressure. The percentage lines elope at different angles. The higher the percentage, the more rapidly does the height of the cap decrease under the influence of atmospheric pressure. There is a direct relation between the height of the cap and the increase of percentage, the rate at which the cap lengthens for increase of percentage seems to harmonise with the rate at which the cap droops for increase of pressure. As a result, the difference between the height of the caps of higher percentages is better maintained. It remains more distinct than it does for the caps of lower percentages- Though from a different standpoint, the pressure lines show the same picture. On the 26 in. line the difference between 4 per cent, and 2| per cent, is so small that in itself it could not be estimated. In the colliery it would take an extra- ordinarily keen power of observation to say whether the cap was 1*12 or 1*03 inches high. The significance of these lines lies, of course, in the fact that the caps decrease more or less rapidly in height as the atmospheric pressure—that is to say as the depth of he mine—increases, other things being equal. Suppose the fireman has been taught that 5| per cent, of gas present is shown by a cap of 9£in. When he goes down a mine nearly 300 fathoms deep, if he gets a cap of 5 in., he will report it 4f per cent, of gas. Under the same circumstances he will report that he met 2| per cent, of gas, when he really found 4| per cent. For a cap of 1 in. he might report anything about | per cent., while it might really indicate anything up to, say, 3 per cent. Of course all these cases are entirely hypothetical, for a variety of reasons; but they are not by any means exaggerated —if anything, the reverse. The firedamp curve is considerably steeper than the coal-gas curve; so when dealing with firedamp these sources of error become crowded into a much smaller space—every error becomes propor- tionately accentuated. The fact of the mine being ventilated slightly alters the argument; but whichever way the question of gas-testing in a deep mine is approached —as long as the safety lamp is the appliance used—the results are bound to be inaccurate. As the simplest and most plausible explanation, the author proposes the following:— The gas cap represents the combustion of the gas in the mixture. We can ignore the flame of the lamp, but bear in mind that the cap depends on the presence of a certain proportion of gas and a certain proportion of air capable of supporting this combustion of the gas. The height of the cap represents the proportion of gas to air, the volume of gas in the mixture. Intensity and shape of the cap are included in the term size. If we compress the mixture, we compress the gas at the same rate. The reduced volume of the gas is expressed by the reduced size of the cap. When the subject was first introduced, Mr. Black con- tended that in an atmosphere of higher pressure the mole- cules of firedamp would be a less distance apart, and that consequently their combustion would extend to a greater distance from the lamp flame, producing a larger cap. This overlooks the fact that the cap is not due to firedamp alone —that its size depends on the proportion between gas and air. Whatever the atmospheric pressure in the mixture, this proportion—this relative distance apart of the mole- cules of gas—remains the same. Mr. Mowat referred to the improved expansion got in an internal - combustion engine owing to higher compression. Explosion in a closed vessel cannot be directly compared with the cap which is formed in conditions where not even complete inflammation takes place. And yet it seems impossible to deny a connec- tion between the two, which leads back to the explanation just given. The efficiency of the internal-combustion engine and the height of the cap both depend on the calorific value of the mixture. Dr. Thornton, of Newcastle, evidently bearing in mind Favre and Silbermann’s and Prof. Andrew's work, had expressed the opinion that the higher the calorific value of the gas, the smaller might be the flame—that is to say, the gas cap. In the compressed mixture we get a greater heat for the same volume of gas. As the height of the cap varies inversely as the heat of the combustion of the mixture, the cap decreases in size as the pressure increases. Increase of pressure has no effect on the oil flame when no gas is presentbut when testing mixtures of air and gas under varying pressure the flame has to be reduced as the pressure increases if it is to render a proper test flame. As the pressure increases, this flame changes; whether it increases merely in luminosity or whether it increases in height also has not been observed, unfortunately. There is merely the record of the fact that the wick has to be pulled down as the pressure goes up, and vice versa, if the standard flame is to be maintained. The significance of this effect of pressure was that the distinction between those percentages of gas, which are likely to be met with in collieries, becomes increasingly difficult as the atmospheric pressure increases. The per- centage is bound to be understated if measured only by the standard, which has been acquired in the laboratory, by the authorised standard. If the lines as now got from experi- ment continue in anything like a similar manner—and there seems no reason why there should be any appreciable change—a point will arrive, and arrive very much sooner for moderate percentages than for high percentages, at which it will no longer be possible to estimate, perhaps not even be possible to detect the presence of gas in the atmosphere circulating through the workings. The action of heat may render the cap more visible or the reverse—it cannot entirely counteract the effect of the increase of pressure. And of course the effect is bound to be there in the opposite direction. If the atmosphere be rarefied, the cap will grow longer. There is a limit put to