The Optical Magic Lantern Journal (February 1890)

‘Tho Optical Magic Lantern Journal and Photographic Enlarger, ‘purpose of holding the supply of oxygen, the quantity of gas may readily be approximated at a glance, but with the cylinder, mistakes are liable to happen, and one is placed in a predicament when giving an exhibition to find that a gas bottle, which: was supposed to contain Say ten cubic feet of gas, had in reality only two or ‘three feet. Ifa further supply is at hand the substituting of one bottle for another is neither a difficult nor a long task, but to find that the supply has ceased in the midst of an entertainment and no more gas is to be obtained in the neighbourhood, places both the Jecturer and the operator in an awkward position. At a recent lecture given by Dr. Dallinger at New Court Congregational Church, Tollington Park, N., the lecture, which was illustrated by means of the Jantern, had not progressed far before it was apparent that the oxygen had given out, and no further supply being at hand, messengers had to be despatched to try and obtain another cylinder in the neighbourhood. ‘During the interim Mr. McDougall addressed the meeting on his recent action in connection with music halls. It having been ascertained that no oxygen could be obtained within reasonable time, it was ultimately announced that the audience could either have the entrance money returned or be supplied with tickets for a subsequent date. Many firms makea practice of gauging the quantity of gas contained in each cylinder at the time it is delivered, but when part of the contents only are used on one occasion, it is well for the operator to satisfy himself before using from it a second time that it contains a sufficient supply for his purpose. When the cylinder is “hired,” it might be found advantageous to also hire a gauge. Those who buy their cylinders outright will naturally possess themselves of the means of arriving at the contents. ‘oO: Odds and Ends. “ When found, make a note of.” IN a recent number an enquirer asked how to ascertain the quantity of oxygen gas in a steel cylinder. The obvious reply was a reference toa pressure gauge, but it may be of interest to many to know that this adjunct, though useful, is not a necessity. A plan which has often been found of value, and which was described in the British Fournul of Photography some time since, consists of simply weighing the gas. The operation is ‘as follows : Weigh accurately the cylinder as received, say 16lb. 20z.; weigh it again after using—result, say 15lb. 90z.; quantity used, 90z. As each ounceof oxygen Tepresents ‘7 of a foot, 9 by ‘7 is equal to 6°3, or about 64ft. of gas used, and the balance stillon hand. Ifthe cylinder be the users own, it is convenient to keep a note of its weight empty, and then the actual weight ‘will give the quantity of gas in stock, and will enable the user to check the quantity of gas supplied when the cylinder is sent to be filled. I keep all the weights -of my cylinders in this way, and have always found good weight from the “ Brins” Company. ‘MESSRS. VEVERS, of Leeds, have no doubt seen it to ‘be a good business notion to publish coloured strips for binding lantern slides, but it must not be supposed, 69 as suggested by “ Bull’s Eye,” that the idea is new or original. It has been in use in the North London Photographic Society for a long while, having been introduced by one of their members and noticed in the journals some two years ago. Other London societies have also worked on the same lines until the fashion has spread from London to Leeds. Ft * * I am glad that the value of paste v. gum is being asserted in this connection. The other day I had to exhibit a number of slides from a well known London house, and the dilapidated condition of the bindings was a fruitful source of difficulty. “The repeated heating of the slides in lanterns had made the gum chippy, and some slides were almost unclothed, while others were ragged. I have never found this happen with good paste, which sticks at once, does not require the slips to be prepared beforehand, and will stand any reasonable wear and tear. x ti * So benzoline is to beat ether for light producing. Mr. Scott, no doubt, in his paper, describes his own experience, but it certainly runs somewhat counter to the usually accepted opinion that pure hydrogen gives a greater heat than carburetted -hydrogen or coal gas. Coal gas hitherto has been considered as a substitute for the pure article, but it now seems that the idea is all wrong. Certainly it is the addition of the carbon that produces the light under ordinary conditions, and the more carbon (within practicable limits) the more light ; but in the oxy-hydrogen light the conditions are so largely altered that experience is needed to determine which has the advantage. Meanwhile it is of interest to notice that the process of enriching coal-gas with hydro-carbon by means of a saturator is not new, but has formed an important feature of various gas processes for many years, as for example the “ air gas” process of, say, fifteen years ago, and several others since. THE SHOWMAN. 10: Railway Station Advertising by Means of the Lantern. FRAMES of about four feet square are shortly to be erected at the principal railway stations in this country for the purpose of displaying certain transparencies for advertising purposes. The frame alluded to is to contain a sheet of opal glass, upon which, at night-time, the picture is to be projected, but instead of the optical arrangements being placed in front of the screen they are situated directly behind it, and the image of the slide thrown by means of reflection. The illumination is obtained from an ordinary gas burner, immediately in front of which is placed the condenser. Then in turn comes a disc nearly the full size of the frame, which contains about two dozen apertures in which may be fixed the slides for. exhibition. This slide disc is rotated by suitable clockwork, which allows of each advertisement being left in front of the condenser for halfa minute. At the requisite distance in front of the slide is placed the lens by which the image is projected upon a circular mirror in front, inclined at the necessary angle to reflect on to the opal glass, which serves as the screen.