The Optical Magic Lantern Journal (March 1897)

The Optical Magic Lantern Journal and Photographic Enlarger. 45 exceedingly minute, and that after a time they get partially obstructed. Burners passing more than 1 cubic foot per hour would yield so intense a light as to be practically unuseable for purposes of domestic illumination. Using a burner which supplied 1 cubic foot of acetylene per hour, an illumination equal to that from thirty standard sperm candles was obtained, and this is equal to fifteen to thirty times as much light as can be derived from ordinary coal gas. One very valuable feature in connection with the new gas is that where it is used there is farless vitiation of the atmosphere than is the case with coal gas. This, of course, is owing to the fact that, for a given illumination, a far greater volume of coal gas requires to be burned than is the case with acetylene. And with a good quality of acetylene, generated from carefully prepared calcium carbide, this results in a great improvement of the atmosphere of dwelling-rooms; with flat flame No. 4 burners, for instance, giving an illumination with coal gas of fortyeight candles, more than five times as much carbonic acid would be produced and poured into the air of a room than would be given off by acetylene burners yielding the same amount of light; and another point of interest is, that although acetylene burns with a very hot flame, yet owing to the small number of lights required, the temperature of the room is not so greatly increased as when coal gas is the illuminant in use. These facts go to show that at any rate the consumers of acetylene should derive certain benofits on the score of health. As to the mode in which the gas should be generated, much has yet to be learnt, and great improvements will, no doubt, be effected in the future as to the mechanical arrangements for its production; at the present time there are many different forms of generating devices upon the market, some of which are no doubt faulty both in design and construction. Further experience will show the best form of appliances to be used. At present the best plan is apparently to obtain the apparatus and materials through well-known and respectable Tirms, whose care for their own reputation lead them to supply only such appliances as are thoroughly well made and tested before being sent out from their works. In fact, the ease and simplicity with which the gas can be manufactured have already led to at least one accident, which probably would not have occurred at all had the apparatus been of a more reliable nature. There are at present two methods by which acetylene may be obtained for use. The first is to employ an efficient generating apparatus, and to charge it as required with the proper quantity of calcium carbide and water. The second method is to procure compressed acetylene from manufacturers in steel tubes, and to attach one of these tubes to a regulating apparatus and the services pipes. As to the latter method, acetylene gas can be compressed into a liquid form at the temperature of the freezing point, under a pressure of 21} atmospheres, or about 320 lbs. to the square inch, but at highcr temperatures the pressure in the cylinders increases tremendously ; at the ordinary temperature the pressure is twice as great, whilst at temperatures of 90 to 100 degrces Fahrenheit, the critical point is reached, according to Villard, and above these temperatures acetylene can no longer exist in liquid form. Liquid acetylene ig not only explosive when allowed to expand again into gas, and mixed with the necessary quantity of air and ignited; it is also possible for it to decompose into its constituent elements, carbon and hydrogen, and as this decomposition is attended by great heat, the pressure is thereby enormously increased. Nevertheless, M. Pictet, whose work in connection with the liquefaction of gases entitles him to speak with great authority, held the opinion a short time ago that if the liquid acetylene is absolutely pure it is deprived of its dangerous qualities. And according to the Engineer, if that be so, his theory, as well as that of other experts, is shaken by the fact that one of his receptacles should have exploded. The gas’ is liquefied in a Cailletet cylinder under a constant and uniform pressure, a condition which is held to be indispensable for transporting acetylene over long distances. These cylinders are made of nickel steel, and are tested up to 250 atmospheres. The material used is so tough that a cylinder having a capacity of twelve litres, or rather more than 2} gallons, does not weigh more than twenty-two kilogrammes, or about 484 lbs. Ina receptacle of this capacity it is only possible to put about 8% lbs. of liquid acetylene, ae some allowance has to be made for its enormous expansion. M. Pictet has had the idea that these cylinders would be sold in all the stores, and would be taken home by the consumers and, after being fixed to a regulator, would be connected by pipes with the burners. The pressure in the cylinders would be sufficient to force the last drop of liquid into the regulator, where it would be volatilised. It wae a receptacle of this description, though of much larger capacity, that exploded in the works in the Rue Championnet. In the form of a steel shell, it was about a metre in length, and had an aperture of only three millimetres (which was closed with a screw plug). No one knows the exact state of the cylinder, but it is presumed that it must have been full at the time of the explosion which took place in M. Pictet’s works in Paris, a part of the works was blown down, two workmen were killed and another injured, and not a pane of glass was left in the windows of the large block of buildings, the unfortunate workmen being torn to pieces and parts of their bodies scattered about the yard. The explosion is believed to have been caused by one of the men closing the screw plug and then trying to open it again. A few minutes before the accident, a man from the engine-room, close by, entered the gas-holder room and saw one of the deceased workmen screwing down the plug, and as a spanner was found among the débris it is presumed that he tried to unscrew the plug by this means, during the process of which he overheated the metal to an extent sufficient to ignite the liquid. The following note on the explosive properties of acetylene has been recently presented to the French Academy by M.M. Berthelot and Vieille, who state that in acetylene at ordinary pressures neither an electric spark, or flame, nor an explosion of a detonating material such as a fulminate, will cause more than a local dissociation of the gas (a fact already established by Professor H. B. Dixon of this city), but that if the gas be compressed beyond two atmospheres, the dissociation, once started, is propagated without sensible diminution throughout the whole quantity of gas. In this way, dissociation of the gas was effected in a tube twenty millimetres in diameter and four metres long. The acetylene splits up into pure hydrogen and a friable mass of carbon, which forms a cast of the containing vessel, and can be withdrawn intact. Ata pressure of 20 atmospheres, which is about half the tension of the saturated vapour of liquid acetylene at twenty degrees C., the explosion develops a