Motion picture handbook; a guide for managers and operators of motion picture theatres ([c1916])

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FOR MANAGERS AND OPERATORS 679 the hydrogen, light it at the burner-tip with a match, just as you would light an ordinary gas jet. Caution: // using tank gas, remember it is under heavy pressure, and, if there .is no reducing valve, open the tank valve very carefully. Turn on sufficient hydrogen to make a flame two, three, or four inches long (only an experiment can determine the proper length of hydrogen flame, as it will vary with size of tip, with different lots of gas and with the individual operator's ideas) and, while slowly rotating the lime allow the flame to play on it until well heated. This is very necessary, particularly with a new lime and with lime of the larger diameters, since if the full strength of the oxygen-hydrogen flame be concentrated on a spot on a cold lime the latter is very apt to crack. When the lime is thoroughly warmed, advance it to within about one-eighth inch of the burner tip, and then, without altering the hydrogen flame, carefully and very slowly turn on the oxygen gas. The flame will at once diminish in size, and a spot on the lime will become incandescent. Keep turning on oxygen very slowly, until there is a slight hissing, whereupon ease off on the oxygen just a trifle until the hissing barely stops. Some operators prefer their light at a point where it does hiss just a trifle, but I think more light is had just at the point when hissing is about to begin. The beginner may now, without any film in, projecting the clear, white light to the screen, turn just a little more hydrogen, and again bring the light to the hissing point by adding oxygen. If the screen brilliance is increased, continue the process until there is no further gain. If, on the other hand, the screen brilliancy is less, then try reducing the mixture by first shutting off a little oxygen, and then a little hydrogen. Keep this up until you find exactly what mixture gives the greatest screen brilliancy, whereupon shut off the oxygen and carefully note length of hydrogen flame. Having done this you will be able to tell pretty closely what length of hydrogen flame will give best results, which will be a help every time you start the light thereafter. Some operators turn on oxygen until a slight red fringe appears at the top of the spot on the lime. I cannot recommend this method, however, as being very accurate. When turning on the oxygen, if the light should go out with a loud snap, or popping sound, quickly turn off the oxygen, relight the hydrogen with a match, and again slowly turn on the oxygen. See "Popping" or "Snapping," Page 680.