The motion picture projectionist (Nov 1929-Oct 1930)

October, 1930 Motion Picture Projectionist 45 cerned with the sizes of the fuses that protect the outgoing d.c. feeder, and if these fuses do not exceed the capacity of the feeder, the job is passed. After the inspector leaves the job, however, it is a simple matter, by the use of refillable fuses, to insert additional links having capacities two or three times greater. This is a most unfortunate condition which only frequent re-inspection can eliminate. It would, therefore, seem advisable that the inspectors on their periodic visits to the theaters check the fuses on d.c. motor generator feeds. Many of the chain theater construction departments now specify wire no smaller than 500,000 circular mills for the d.c. booth feeders. These have a capacity of 400 amperes per leg, and are usually large enough to carry two projection machine arcs and one stereopticon or spotlight simultaneously. Mr. R. C. Hubbard: In connection with the matter of switches and fixtures in film handling rooms, Mr. Manheimer solicits information regarding the explosive gases given off by film. I think we should go on record with the fact that no explosive gases are given off by film until it becomes heated to abnormal temperatures and that there is, therefore, no necessity for vapor proof fixtures in film handling rooms. Mr. Manheimer: I should like that particular point settled at this meeting. Dr. Sease (Communicated) : In connection with that part of Mr. Manheimer's paper that seems to solicit some definite information regarding the explosiveness of gases given off by film, I consider that the vapors in a film vault of average size filled with film under average conditions will not be explosive or combustible. The vapor to be found is largely acetone. The acetone in the film may be as high as 2 per cent. It is usually much less. This acetone is very hard to remove and would require quite high temperatures to get it out of the film. According to our information, vapors of acetone are not explosive until the acetone content of the air is 3.7 lbs. per 1,000 cubic feet. We have no information on the accumulation of vapors in a vault which has remained closed a long time, but it is possible that the vapors may increase if the vault is practically hermetically sealed. We know of no spontaneous combustion of vapors from film, nor have we had in our experience any fire caused by the ignition of vapors emanating from film. There are records of fires having been caused by static discharges over mixers into which solvents were being run. While the vapor from film is largely acetone there is some alcohol, camphor, and fusel oil. These vapors have higher specific gravity than air, and, therefore, tend to settle. It is possible that the vapor proof globe requirements have been established to reduce the hazard of igniting film by its contact with an incandescent lamp. Celluloid film ignites in a very short time at 300 deg. F. At 212 deg. F. it will not ignite for a considerable time. At 140 deg. F. we have observed its decomposition without ignition in five or six months. Hoffmann ^foons ' PERF^JiQN Modern industry becomes more exacting every year, and Perfection Rheostats, the highest standard that scientific construction can produce — maintains its leadership through our never-ceasing research for improvements, no matter how slight. "The only Union-Made rheostats" mean more than mere words. HOFFMANN & SOONS Mfg. Division 387 FIRST AVENUE NEW YORK Contracting Electrical Engineers — Moving Picture Theatre Electrical Specialists THE BIFOCAL F:2.0 SUPER-LITE LENS Adjustable FOR BOTH SILENT AND SOUND FILM V2" and %" Variation in E. F. AS the name implies this new construction offers the projectionist everything he has been looking for; two focal lengths in one construction. By rotating the ring on the lens mount the size of the image on the screen can be increased or decreased instantly to take care of the difference between sound and silent film. At the same time an automatic shifting of the center of picture on screen with sound film is provided for. PROJECTION OPTICS CO., INC. 330 Lyell Ave., Rochester, N. Y., U. S. A.