38 THE COLLIERY GUARDIAN. January 2, 1914 Experimental Research Work on Safety Lamps. (Report by Dr. R. V. Wheeler.) The following is an account of experiments that have been carried out at your request regarding the passage of the flame of an explosion through the gauze of a safety lamp. With an ordinary hewer’s lamp fitted with two gauzes of standard wire and mesh it is generally impossible to cause the flame of an explosion within the lamp to pass into and ignite an explosive mixture outside, unless the current of explosive is passing the lamp at a high velocity. The hewer’s lamp is, however, of comparatively small size—the distance between the wick and the bottom of the gauze chimney rarely exceeds 3 in., and the gauze chimney itself is rarely more than Sin. in length. The question arises whether a lamp of larger size, such as a pit bottom lamp, is equally as safe in a (still) explosive atmosphere as is a hewer’s lamp; and, if so, what is the limiting size above which the lamp becomes dangerous. A number of experiments have been carried out to test this point and also to obtain some information regarding the relative safety of lamps fitted with a single and with a double gauze. The method of experimenting, which is described in detail later, was, briefly, to ignite explosive mixtures of either coal gas and air, or pure methane and air in brass cylinders of different lengths, closed at one end and fitted with gauze discs stretched across the other end. The mixtures were ignited by the spark from an induction coil passing between electrodes fixed centrally, 1 in. from the closed end of the cylinders. From the results obtained, the general conclusions to be drawn are as follow :— (1) With two gauzes, no matter how arranged—e.g., whether in close contact, with the strands either crossed or superposed; or separated by any distance up to half- an inch the flame of the most explosive mixture of methane and air (about 10 per cent, methane) does not pass through to the outside atmosphere when the point of ignition and the gauze is 9 in. or less. When the distance is 12 in. or more, flame may pass through two gauzes, no matter how placed, and may ignite an explosive mixture outside. It would thus appear that, to ensure absolute safety, there should not be a greater distance than 9 in. between the wick of a lamp and the top of the gauze chimney. It is true that, with a safety lamp, release of the pressure of an internal explosion begins to take place as soon as the bottom of the gauze chimney is reached; but if the whole lamp, including the gauze, be presumed to be filled with an explosive mixture, and ignition take place at the wick, the speed at which the flame travels throughout the gauze chimney cannot be regarded as suffering much diminu- tion, especially with a bonneted lamp. On the other hand, the conditions that could suddenly produce, in practice, the most explosive mixture of methane and air inside a lighted safety lamp would be rather remarkable. That they are possible, however, has been pointed out by Marsaut in his work “ Etude sur la Lampe de Surete des Mineurs.” (2) With a single gauze, the flame of the most explosive mixture of methane and air does not pass through to the outside atmosphere when the distance between the point of ignition and the gauze is 2 in. or less ; but the flame passes through a single gauze, and can ignite an explosive mixture outside when the distance between the point of ignition and the gauze is 3 in. or more. (3) Under certain conditions other than those defined in conclusion (1) as safe, flames which do not pass through two gauzes when those gauzes are in close contact may p^ss through if the gauzes are separated by as little as 0’002 in. For the two gauzes to prevent the passage of such flames it is necessary for them to be in close contact, but it does not matter whether the strands of the gauzes be crossed or superposed, flame will not pass through in either case. This seems to point to the possibility of obtaining safety, equal with that of double gauzes, by means of a single gauze made from wire double the “ width ” of that ordinarily employed, or from perforated sheets of double the thickness or ordinary gauze sheet. Such a gauze would, to a certain degree, reproduce Davy’s original idea of a bundle of tubes. (4) The flame arising from the most explosive mixture of coal gas and air (about 15 per cent, coal gas) can pass through two gauzes, no matter how placed, and ignite an explosive mixture outside, when the distance between the point of ignition and the gauzes is only 8 in., and 5 in. is sufficient unless the gauzes are in close contact. These results are thus very different from those obtained with the most explosive mixture of methane and air, and show the fallacy of drawing conclusions respecting the behaviour of safety lamps in mine atmospheres from experiments made with coal gas and air mixtures. On the other hand, experiments with explosive mixtures of petroleum ether and air gave the same results as with methane and air mixtures for the limiting distance between the point of ignition and the gauze (whether single or double) that would enable flame to pass through. Brass cylinders of different lengths, 3in. in diameter, were fitted with insulated firing points at the bottom, which was closed, and carried at the top an arrangement for fitting gauze discs. In some experiments these gauze discs communicated to the outside air, and whether or no flame passed through was judged by observation in a darkened room (apparatus No. 1); in others a glass cylinder, 12 in. long, formed a continuation beyond the gauzes and, this cylinder being also filled with explosive mixture, the transmission of flame through the gauzes would be followed by an explosion beyond (apparatus No. 2). • The explosive mixtures were prepared in large gas- holders and the cylinders were filled by passing a rapid stream of the mixture through them, entrance being at the top. A volume of the mixture three or four times that of the cylinders was employed for sweeping out the air originally contained in them, the tops being closed during this process by a brass cap or a ground glass plate. These covers were removed, and the tubulures that afforded entrance and exit of the current of explo- sive mixture closed, just before firing. Ignition was caused by the passage of sparks from an induction coil between brass electrodes | in. apart fixed 1 in. from the closed ends of the cylinders. With mixtures of coal gas and air it was easy to judge with apparatus No. 1 whether or no flames passed through the gauges, owing to their luminosity; but with methane and air it was sometimes difficult to decide, a faint glow, which might or might not be a flame capable of igniting an explosive mixture, being all that was visible. Apparatus No. 2 was requisitioned in such cases. Series I.—Experiments with Coal Gas.—The coal gas had the following average composition :— Carbon dioxide.............. Trace Benzene and ethylene hydrocarbons 4 0 per cent, by volume Carbon monoxide................ 7 0 per cent, by volume Hydrogen...................... 51’0 per cent, by volume Methane....................... 32 0 per cent, by volume Ethane ....................... 3 0 per cent, by volume Nitrogen ..................... 3 0 per cent, by volume (a) Distance between point of ignition and gauzes = 18 in. Percentage of coal gas in mixture = 12 per cent. A large flame passed through under the following conditions:— (i.) Single gauze. (ii.) Two gauzes in close contact, strands superposed. (iii.) Two gauzes in close contact, strands crossed. (iv.) Two gauzes, separated by a space of lin. (v.) Two gauzes, separated by a space of J in. (b) Distance between point of ignition and gauzes = 12 in. Percentage of coal gas in mixture =z 11 per cent. A large flame passed through under the following conditions:— (i.) Two gauzes in contact, strands superposed. (ii.) Two gauzes in contact, strands crossed. (iii.) Two gauzes, separated by a space of 1 in. (iv.) Two gauzes, separated by a space of J in. (c) Distance between point of ignition and gauzes = 9 in. Percentage of coal gas in mixture = 15 per cent. A large flame passed through with two gauzes in contact, with strands either superposed or crossed. (d) Distance between point of ignition and gauzes ~ 6 in. Percentage of coal gas in mixture = 15 per cent. Conditions. Result. (i.) Two gauzes in contact, strands Flame did not pass superposed (ii.) Two gauzes in contact, strands Flame did not pass crossed (iii.) Single gauze.......... (iv.) Two gauzes, separated space of i in. (v.) Two gauzes, separated space of 1 in. (vi.) Two gauzes, separated space of in. (vii.) Two gauzes, separated space of jL- in. (viii.) Two gauzes, separated space of g3T in. (ix.) Two gauzes, separated space of 0 002 in. ..... Large flame passed by a Large flame passed by a Large flame passed by a Large flame passed by a Flame passed by a Flame passed by a Small flame passed All the experiments in Series I. were repeated three or four times, and in the case of the experiments with the 6 in. distance six or eight times with the same results. Series II.—Experiments with Methane.—The methane was prepared from pure aluminium carbide and purified (a) from acetylene by passage through ammoniacal cupreous chloride solution, and (5) from hydrogen by passage over oxidised palladium precipitate heated at 90degs.Cent. (a) Distance between point of ignition and gauzes ............................. = 12 in. Percentage of methane in mixture..... =95 per cent. Conditions. Result. (i.) Two gauzes in contact, strands No flame passed in superposed three experiments, small flame in two (ii.) Two gauzes in contact, strands No flame passed in crossed three experiments, small flame in one (iii.) Two gauzes, separated by a Small flame passed space of 1 in. (iv.) Two gauzes, separated by a Small flame passed space of «in. Experiments were also made in which fine coaldust was strewn in small quantity between two gauzes | in. apart. A small flame and sparks of burning coaldust passed through. (b) Distance between point of ignition and gauzes ......................... — 12 in. Percentage of methane in mixture.... — 7’5 per cent. Conditions. (i.) Two gauzes in contact, strands superposed (ii.) Two gauzes in contact, strands crossed (iii.) Two gauzes, separated by a space of -4- in. (iv.) Two gauzes, separated by a space of | in. (v.) Two gauzes, separated by a space of 2 in., with fine coal- dust between gauzes Result. No flame passed No flame passed No flame passed Small .flame passed Small flame passed (c) Distance between point of ignition and gauzes .........1................. — 9 in. Percentage of methane in mixture.... =9’5 per cent. Conditions. Result. (i.) Single gauze................... Flame passed (ii.) Two gauzes in contact, strands No flame passed superposed (iii.) Two gauzes in contact, strands No flame passed crossed (iv.) Two gauzes, separated by a space No flame passed of t¥ (v.) Two gauzes, separated by a space No flame passed of J in. (vi.) Two gauzes, separated by a space No flame passed of 4 in. (vii.) Two gauzes, separated by a space No flame passed of I in., with coaldust between gauzes (d) Distance between point of ignition and gauzes ........................... = 6 in. Percentage of methane in mixture... =10 per cent. With two gauzes, no flame passed through under any of the conditions described in series (c) above. (e) Experiments with a single gauze :— Percentage of methane in mixture = 10 per cent. Distance between gauze and p point of ignition. esu t. 6 in...................... Flame passed 4 in...................... Flame passed 3 in...................... Plame passed 2 in...................... No flame passed All the experiments in Series II. were repeated four or five times. The experimental work described in this report has been carried out by Mr. M. J. Burgess. BOOK NOTICES. A Manual of Ambulance. By J. Scott Riddell. Sixth edition, enlarged. 8| in. by 5J in.; xvi. fl- 254 pp., 212 figs. London : Charles Griffin and Co. Price 6s. net. This, the sixth edition of Mr. Scott Riddell’s well- known manual of ambulance, has been much enlarged and specially prepared for the use of voluntary aid detachments. The author has devoted much space to the subject of ambulance transport and the work of voluntary aid detachments. He shows how a body of men trained in first-aid work can fill in the gap which now exists between the Royal Army Medical Corps, Territorial Force organisation and the base hospital. At the present time the Territorial medical force would collect and bring the wounded from the front to a clearing hospital. This clearing hospital and the area up to the general hospital could be manned by voluntary aid detachments. There is no doubt that much valuable work could be done by such a service, should the occasion unfortunately arise. The author has, however, quite omitted to provide special advice for the emergencies which daily, and even hourly, arise in the colliery practice of Great Britain. In this edition, which has been greatly enlarged and increased in price, there is no special reference to the treatment of accidents arising in mines. The inclusion of the 16 X-ray photographs, and the cost involved in their production, is quite unjustified in a manual of ambulance. The interpretation of X-ray photographs is difficult enough for an expert, and the photographs themselves cannot teach a first-aid student as much as a plain drawing. If the space occupied by these plates had been taken by a chapter on the special treatment and transport of persons injured in mines, on rescue work and the training at rescue stations, a more valuable text book would have been written.