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FOR MANAGERS AND OPERATORS 681
to form a depression on its face, called a "Pit." As this pit has the effect of altering the distance cf the lime from the burner tip, it affects the light brilliancy, and it is necessary occasionally (time varies between two and five minutes, depending on hardness of lime and force of gas jet) to revolve the lime just enough to move the pit out from in front of the jet and present a new surface to the flame. In doing this revolve the lime very slowly, so that the new surface will have time to come up to incandescence as the old one cools off, else you will produce a decidedly bad effect on the screen.
Hissing or Roaring. — Some operators supply their jet enough oxygen to cause the light to hiss very slightly. Should there be a loud hissing (some call it "roaring") it may be due to (a) Excess of oxygen, in which case the light is apt suddenly to go out with a loud pop, or snap. If this occurs turn off oxygen quickly (see "Popping or Snapping") relight the hydrogen and again turn .on the oxygen, (b) Interior wall of burner jet rough. Remedy: New jet. (c) Too much gas for size of jet. Remedy: Reduce gas. (d) Wrong distance between tip of burner and lime. Remedy: Alter distance. A deep pit in lime has this effect, and if the lamp begins to hiss, without any adjustment having been altered, the probable cause is a deep pit, and revolving the lime will remedy matters.
Adjusting the Lamp. — The light must be centered with the condenser, precisely as in the case of the electric arc. If it be too far away, too close, too high, too low or too far to one side, the screen illumination will be uneven, and there will be shadows. By means of the adjustments provided, move your lamp up, down or sidewise until the screen L evenly illuminated all over, and there is no trace of shadow. The Condenser. — The condenser used for limelight is the same as for the electric arc. It is customary to carry the spot a trifle larger than with electricity, due to excessive area of light source with consequent "fuzzy" edges of spot at cooling plate and use two 6*/2 lenses, located as close to the aperture as they can get them. Whether or not this is the best practice I am not prepared to say, but presume it is, as it is much used. One operator even advises altering the outfit, if necessary, so as to get the lamphouse cone right up against the machine aperture, shoving it to one side to change films. This does not seem to the author like good practice, but try it out anyhow. I would suppose this closeness would require the locating of the light too far from the