The Optical Magic Lantern Journal (February 1892)

22 The Optiosl Magio Lantorn Journal and Photographic Halarger. of oxygen, this would probably ignite at a comparatively low temperature. Th2 temperature of any oilin the tube may even be materially increased by friction resulting from the in-rushing gas ; or the particles of oil, carried furward with yreat violence, might become heated by friction against the sides of the tube and by the sudden impact with the end of the passage; and all these circumstances would increase the danger of explosion. Since the danger of the presence of oilin these gauge tubes has come to be realised, we have discontinued the practice of using oil for dividing and testing these gauges, pumps filled with water having been adopted instead ; and the greatest care is exercised to prevent any oil from coming into contact with the gauge fittings during manufactiire. Special water pumps are now set aside purposely for this work, and the connexions are so arranged that it is impossible for any workman to screw the gauges on to an oil pump without providing himself with a special connexion for this purpose—all chances of a mistake being thas overcome. The pamps themselves are fed from the town's main, and, after each test, the contents of the pumps are discharged into a white enamelled trough, in which any traces of oil can be easily be detected. Subsequently, the contents of the tube are extracted by means ofa vacuum pump, and are examined for oil. Finally, the remnants are blown out by admitting air pressure to the gauge at 100 or 120 atmospheres, and suddenly releasing this pressure. In this manner, everything that foresight can provide is done to minimise the chances of the tube containing, when completed, even the slightest traces of oil. Bat, in spite of every care, the entire absence of oil or other inflammable matter cannot be absolutely assured ; and, even if this were done, there always remains the danger of oil gaining access to the tube accidentally when a gauge is in use. Therefore, whilst continuing to exercise every care to keep away all traces of oil, the ultimate safeguard against accidents of this description must be looked for in another direction— namely, by checking the sudden in-rush of gas to the gauge when opening the valve, so that the pressure in the gauge rises gradually,and the heat evolved has time to be absorbed by the material of the gauge tube. This may be accomplished by opening the valve very gently ; but, as this gentleness cannot always be ensured, owing to the frequent stiffness of the valves, carelessness, and want of skill, it is indispensable, in order to secure perfect safety, to fit each gauge with some means for auto matically checking the admission ; and, whatever check | is employed for this purpose, it mast not require any j particular attention or manipulation. Various devices have been brought out for this purpose; but, of al! that have come within the limit of my experience, the check patented by Mr. W, M. Jackson, of the Manchester Oxygen Company, is by far the simplest and best. This consists in screwing a plug, through the centre of which a fine hole has been drilled, into the foot of the connecting shank of the gauge. Upon this plug are placed a number of alternate layers of copper wire gauze and felt cloth, in the manner shown in the illustration. Another screwed plug, similarly drilled with a fine hole, is then added, and the alternate layers of gauze and felt are compressed between the plags. This packing retards she pressure of the gas, even when suddenly turned on; but it does not prevent the ultimate admission of full pressure to the gange. Iam of opinion that absolute immunity from danger of chemical explosions in gauges can be ensured by the proper use of this check, and it is not too much to say that no gauge used for this purpose should be without it or sOme equivalent device which has proved satisfactory. If a pressure gauge is of sound construction and well made, and fitted with the adjuncts which I have described. and these are kept in proper working order, it may, I think, be accepted that such an instrument is absolutely safe, and there need be no fear of any accident from known causes, The experiment which I have performed before you suggests, however, that even without the use of a pressure gauge an explosion in the connections is possible, provided the end of the passages in the connection is sealed and the pressure suddenly admitted. Generally speaking, the regulator valve is full open when the cylinder valve is being opened, and there is, then, little danger of heating in the regulator connection; but circumstances might arise in which pressure is suddenly admitted with the regulator valve closed, and here the conditions are precisely similar to those which exist in the cases of gauge chemical explosions. This might, for instance, occur if the valve is opened twice in succession, the first opening having been sufficient to set the regulator to work. If the pressure is then released and readmitted suddenly, an ignition might occur in the regulator connexion. It appears to me that the same thing might happen in using a cylinder valve which is not quite true, and which is Worn to an oval shape in the seating. If such a valve is opened, a puff of oxygen sufficient to fill the regulator might be passed, followed by a temporary closing, whereupon a.suddea opening might produce in the regulator counexion the precise conditions for an explosion. These considerations suggest the theory that some of the explosions which have been attributed to pressure gauges have probubly originated in the connexion of the regulator itself. The danger under consideration can be minimised by making the connexion to the regulator as short as possible ; and, generally speaking, long passages of any kind between the cylinder valve and the regulator or gauge should be rigorously avoided, as constituting a decided source of danger ; and, wherever it is necessary to have a long passage, the end of which is or may become sealed, a check should be provided. If lanternists would only devote their attention to these points, and assure themselves that the principles here laid down are carefully carried out, we shall have no more explosions ; and my labour in preparing this paper will have been amply rewarded if it should have theeffect of arousing the members of this Suciety, and through their medium other lanternists, to the importance, of carefully studying this subject. ‘ot Editorial Table. “THE Oprics Of PHOTOGRAPHY AND PHOrOGRAPHIC LENS.”—(London: Whittaker and Co.). In this work the author (Mr. J. Traill Taylor), who is well known as having occupied the editorial chair of The British Journal of Photography for nearly thirty years, has brought the subject down to the level of the youngest amateur. [n popular language, capable of being understood by the non-mathematical reader, he explains all about aberration of light when transmitted by lenses, and shows in what manner photographic optics differ from those of the microscope and telescope. He enters fully into the various forms of photographic lenses, and explains the special functions of each class. An historical veswmé of landscape, portrait, and other lenses, with numerous drawings, is given. The nature and cure of distortion is treated of, and the conditions underlying the production of distortion and rectillinearity described. Such defects as characterise modern lenses—as, for example, the flare-spot—is fully explained, and the method for curing it described. Special chapters are devoted