February 25, 1916. THE COLLIERY GUARDIAN. 359 RAPID ESTIMATION OF OXYCEN AhD BLACKDAMP.* By Henry Briggs. The problem of providing the underground official with an appliance for measuring approximately the oxygen or blackdamp percentage in the air of naked light mines has been satisfactorily solved by Dr. J. S. Haldane in his tube-and-paper test.f. No description has been published, honever, of a device for the same purpose, suitable for service in a mine where safety lamps are adopted, and combining the features of simplicity in construction, mechanical strength, speed, and simplicity in operation, and absence of liquids; which features seem necessary when the actual circumstances of use are borne in mind. The arrangement described below possesses these features, and provides a means of estimating oxygen or blackdamp with a sufficient degree of accuracy for many ordinary purposes. The me.hod is not designed altogether to take the place of chemical analysis of samples collected in the mine; it cannot approach the precision of analysis, which will always be the final appeal in eases of doubt or of special importance. It is an approximate method, intended primarily to assist .he fireman in carrying out his statutory duties. Description of Device. The principle involved is that a safety lamp will burn with a smaller inlet passage in air rich in oxygen than in air poor in oxygen, and that the size of rhe inlet can be made a measure of the oxygen percentage. The appliance (which is illustrated in figs. 1 to 3) consists of an adjustable cut-off applied to the inlet of a safety lamp of the improved Gray pattern. The tubes which constitute the usual means of ingress of air to the lamp are stopped, the air being made to enter either through the curved slit A, or 'through the side hole 13. When a test for oxygen is being made, the latter hole is closed by the thumb, the air then having only one entrance, namely, the slit A. This slit is cut in a well- faced brass plate, over which fits a second plate C, of semi-circular shape, and pivoted at its centre. The two plates are held closely together by a small spring. When C is rotated by means of the milled knob attached to it, it gradually cuts off the inlet opening and throttles the air supply to the lamp. In fig. 2, and on the side of the attachment which is turned towards the light, is to be seen the opening D, which exposes the back of the movable pla.e C and the graduations which are engraved on it. There are two graduated scales and two index marks against which the scales are read. These scales are figured from 16'5 to 21, and indicate the percentage of oxygen in the air; the first scale is to be read when the air temperature does not exceed 70 degs. Fahr, (or so), and the second when the temperature is between 70 degs. and 85 degs. Fahr. Once the oxygen percentage is known, the proportion of blackdamp can readily be calculated, if required. It was, however, decided not to indicate blackdamp as well as oxygen—firs., because of possible confusion through having two sets of figures; and, secondly, because oxygen, and not blackdamp, is named in the Act. The lamp has a single circular wick, and burns benzolene. Spirit fuel is necessary in order to avoid charring of the wick, which would render the method impossible. The attachment does not prevent the lamp from being used as a firedamp indicator; in fact, the lamp, as illustrated, is equally serviceable for estimating either oxygen or firedamp. Method of Operation. Fig. 3 shows the lamp being used in measuring the oxygen percentage. The operator turns the inlet open- ing away from him so as to prevent his own breath from entering the lamp and ;hus vitiating the results. He supports the lamp in his left hand, and closes the side opening (B, figs. 1 and 2) with his left thumb. He adjusts the flame to about half its normal height—that is, to t3t, or | in. or so. An exact adjustment of the flame is unnecessary. With his right hand he turns the plate C, rotating it fairly quickly until the flame sinks and all white light fades from it through lack of air; he then proceeds more carefully, turning the milled knob in short jerks, with a gradually lengthening pause between each jerk, until the flame begins the tremulous flickering, or bobbing which is the invariable prelude to its extinction. The operator then lifts his left thumb from the side opening; the flame immediately revives and illuminates the gradations at D (fig. 2); the scale is read, and the oxygen percentage thus obtained. The fireman, in examining the air of his section as to its oxygen content, is concerned in making sure that a place is “ in a fit state for working or passing therein," within the meaning of section 29 (3) of the Coal Mines Act. That is to say, he is interested rather in knowing whether the air contains more than or less than, 19 per cent, of oxygen than in measuring the actual proportion. Because of this, the manner of using the appliance may be simplified still further for the fireman. The scale can be set at 19 per cent., and kept there. If one prefers it, the plates can be held together in this position by a small set-screw. The lamp .then normally takes the greater part of its air supply through the side hole. When the fireman desires to test the air, he lowers the flame to half size and places his thumb on the side hole. If the lamp continues to burn, the air is “ up to standard he removes his thumb, puts up the flame, and goes, on his way. If the flame sinks rapidly, and prepares to go out, the fireman lifts his thumb and * From a paper read before the Mining Inst, of Scotland. I “A Flame-Test for the Estimation of Oxygen and Blackdamp in Naked Light Mines,” by J. S. Haldane, Trans. Inst.M.E., 1911, vol. xli., p. 455. recovers the flame; he then knows that the air does not meet the requirements of the Act. Such a test can be made in half a minute; while the determination of the actual percentage in the manner first described occupies from.one to two minutes. There is no necessity for losing the light in conducting these tests. The official in a safety lamp mine can in any case be trusted to guard his light for evident reasons. Particularly with the second method just described the risk of being left in the dark is quite small, for not only is a flame that shows signs of extinction instantly recoverable; but there is also the fact that it is not often in safety lamp mines that air in which men work or travel, is found to. contain less than 19 per cent, of oxygen; and with percentages above 19 the flame has no tendency to go out. An objection to using the lamp in trying whether the requirements of section 29 of the Act are being main- tained is that the section relates as much to carbon dioxide as to oxygen, and that air in a certain place may be of inferior quality because the carbon dioxide exceeds l.'r per cent., even though its oxygen content is over Fig. 1. 19 per cent. The point is one worth clearing up, as the contention is true enough; it affects work with the Haldane tube as well as with the device here described. A sample of air containing both 19 per cent, of oxygen and 1} per cent, of carbon dioxide is contaminated by 9'22 per cent, of blackdamp. This blackdamp contains 1'25 parts in 9'22, or 13-5 per cent, of carbon dioxide: the remainder is nitrogen if it be assumed that the analysis is expressed in terms of dry air, and nitrogen plus waler vapour if expressed in terms of damp air. If it were known that the blackdamp occurring in a particular seam, or section of the workings in a seam, contained more than 13'5 per cent, of carbon dioxide, one would evidently have to be more on one’s guard against an excess of this gas than against a diminution of oxygen; the 1'25 per cent, limit of the Act would be reached before the 19 per cent, limit. As an example : In samples taken in the St. Ger- maine Colliery, East Lothian, the blackdamp present was found by analysis to contain, on the average, 15’5 per cent, of carbon dioxide. The air in this Table I.—Aquious Vapour in Saturated Air.* (D (2) (3) (4) (1) (2) (3) (4) (1) (2) (3) (4) (1) (2) (3) (4) (1) (2) (4) Temperature. Degs. Fahr. Vapour pressure, in inches of mercury. Differences. Proportion by volume of aqueous vapour; barometer 30 in Temperature. 1 Degs. Fahr. Vapour pressure, in inches of mercury. Differences. Proportion by 1 volume of aqueous vapour; | barometer 30 in. | Temperature. Devs Fahr. Vapour pressure, in inches of mercury. * Differences. Proportion by 1 volume of aqueous vapour; ' barometer 30 in. Temperature. Degs. Fahr Vapour pressure, in inches of mercury. Differences. Proportion by volume of aqueous vapour; barometer 30 in. I Temperature. Degs Fahr. Vapour pressure, in inches of [ mercury. Differences. Proportion by volume of aqueous vapour; barometer 30 in. 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 4V 50 51 52 53 0'181 0T88 0'195 0'203 0'211 0'220 0'229 0'238 0’247 0-256 0-266 0-276 0-287 0’298 0-309 f)'321 0'333 0'316 0'360 0'374 0'388 0'402 7 7 8 8 9 9 9 9 9 10 10 11 11 11 12 12 13 14 14 14 14 15 Per c. 0'60 0 62 0'65 0'68 0'70 0'73 0'76 0'79 0'82 0'85 0'89 0'92 0'96 0'99 1'03 1'07 1'11 1'15 1'20 1'24 1'29 1'34 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 0'417 0 433 0'449 0'465 0'482 0'499 0'517 0'535 C'554 0'574 0 595 0'616 0'638 0'660 0'683 0 707 0'732 0'757 0'783 0'810 0'838. 0'866 16 16 16 17 17 18 18 19 20 21 21 22 22 23 24 25 25 26 27 28 28 30 Per c. 1'39 1'44 1'49 1'55 1'6“ 1'66 1'72 1'78 1'85 1'91 1'98 2'05 2'13 2'20 2'28 2'36 2'44 2'52 2'61 2 70 2'79 2'89 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 0'896 0'926 0'957 0'989 1'022 1'056 1'091 1'127 1'164 1'202 1'241 1'281 1'322 1'364 1'407 1'451 1'496 1 543 1'592 1'644 1'697 1'751 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 47 49 52 53 54 55 Per c. 2'99 3'09 3'19 3'30 3'41 3'52 3'64 3'76 3'88 4'01 4T4 4'27 4'41 4'55 4'69 4'84 4'99 5'14 5'31 5'48 5 66 5'84 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 1'806 1'862 1'919 1'977 2 037 2'098 2'161 2'226 2-293 2-362 2'433 2-505 2'578 2653 2’730 2-809 2 890 2'973 3'058 3'145 3'235 3'327 56 57 58 60 61 63 65 67 69 71 72 73 75 ’77 79 81 83 85 87 90 92 95 Per c. 6'02 6'21 6'40 6'59 6'79 6'99 7'20 7'42 7'64 7'87 8'11 8'35 8'59 8'84 9'10 9'36 9'63 9'91 10'19 10’48 10'78 11'09 120 121 122 1 1 11 1 1 1 1111 1 1 I 11111 to 10 to HON 98 101 1 1 1 1 ' 1 1 1 1 1 1 1 | 1 1 1 ' 1 | O M “ * Derived from Regnault’s Experimental Data. case will hold 1'25 per cent, of carbon dioxide when 19-24 per cent, of oxygen is present, and the fireman can be instructed that air in this section is not up to the statutory requirement unless it contains over 19| per cent, of oxygen; and, when the lamp is used, the index will be set at that figure, instead of at 19. Thus, in order to make the lamp most fully service- able, the composition of the blackdamp should be known, and this involves a few preliminary analyses. The same remark applies to the Haldane tube, and, indeed, to any appliance which gives values for either oxygen or carbon dioxide, but not for both. Precautions. The following precautions must be observed by a user of the lamp :— (1) The cut-off must not be moved too quickly. It is important that the working instructions given above should be closely followed. (2) No reading should be taken until the lamp is hot. A cold lamp gives low values. The lamp should be allowed to burn, with the half-inch working flame, for at least 15 minutes before it is used for the estimation of oxygen. (3) The gauzes must be kept reasonably clean, and the inlet slit not allowed to become choked. (4) The size of the test flame is only of secondary importance. It is preferable, however, not to use a full-sized flame, which is jumpy, and therefore unreli- able, when the air supply is cut down, and normally gives rather high results. The most reliable flame appears to be one of about J in. (5) In a strong air current the inlet opening should be turned towards the return side. Moderate currents have no appreciable influence. (6) In any place where much water drips from the roof, care should be taken that water does not enter the inlet, or else it may seek the lower gauze and form a film over it, causing the device to give low readings. Method of Graduation. The scales of the first model were graduated empiri- cally. Blackdamp was made in varying proportions by burning an alcohol flame inside a wooden chamber. Alcohol creates, according to the chemical equation, a blackdamp containing 15 per cent, of carbon dioxide and 85 per cent, of nitrogen. The average of a number of analyses gave the carbon dioxide constituent as 14-97, a satisfactory verification of the theoretical figure. A preliminary study was made in order to ascertain whether the temperature of the saturated air had an influence on the results given by the lamp. A striking influence was revealed for high temperature, but no difference of importance was found ■with temperatures ranging between 40 and 70 degs. Fahr. The next step was to test thoroughly, by a series of 138 determinations, the scale already marked out, this scale being intended to serve for temperatures below 70 degs. Fahr. Slight adjustments were found neces- sary in places on the original scale, and these were effected. The figures obtained in this portion of the work are set forth in Table II. The temperature ques- tion was then investigated more fully, and the second scale, covering a temperature range of 70 to 85 degs. Fahr., was set out in the same manner as the first. Influence of Water Vapour. As already stated, the lamp scales were calibrated in air saturated, or almost saturated, with moisture. The questions now arise : How is the presence of water vapour to be dealt with? Should the scales be con- structed so as to ignore it, as does the ordinary chemical analysis, or should they be"made to take it into account. Chemical analysis usually gives the percentage of the various gases as they would be if the air were quite free from moisture. It is commonly stated, for example, that fresh air contains 20-93 per cent, of oxygen. This, however, is the figure for dry air, and is not true for atmospheric air; in mine air, indeed, the percentage of aqueous vapour is seldom, if ever, negligible. To take rather an extreme case, saturated fresh air at 85 degs. Fahr, and normal pressure contains 4 per cent, of water