International projectionist (Jan-Dec 1948)

film— ultimately acquires an almost explosive degree of combustion. Actually, however, celluloid does not and cannot explode, either by ignition in a confined space or by percussion. This seems unusual when we stop to consider that guncotton and pyroxylin, both of which burn only slightly more readily than celluloid itself, explode with tremendous violence when struck sharply. (Guncotton sometimes explodes when merely scratched!) The failure of celluloid to exhibit the properties of a true explosive is attributed to its camphor content. To what, then, may reports of film "explosions" be ascribed? (We may ignore the euphemistic fabrications mouthed by some exhibitors and lax fire officials.) Celluloid Degradation Gases Cases of Incomplete Combustion. — Celluloid in a sufficient supply of oxygen burns to form three colorless, odorless gases; viz., carbon dioxide, water vapor, and nitrogen. These gases are non-poisonous, but they can suffocate by excluding the oxygen in the air from the lungs. Under ordinary conditions, however, celluloid — much less gelatin-coated film — never burns without degradation into far more dangerous products. When celluloid is partially confined, as by being enclosed in a container or coated with a less combustible substance, the flame is to some extent smothered because of an inadequate supply of air. But violent chemical reactions continue apace. Some of the unburned celluloid is decomposed by heat into additional gaseous products. (As a matter of fact, the decomposition temperature of celluloid is about 200° F., 100 degrees below the ignition temperature.) The following typical analysis shows by what proportions the celluloid degradation gases are usually present: Carbon monoxide 47% Hydrogen 18 Methane 16 Carbon dioxide 14 Nitrogen 5 100% Explosion of Celluloid Gases. — Of the decomposition gases all are highly inflammable except carbon dioxide and nitrogen. Now, any mixture of air with from 9 to 30% of the celluloid gases constitutes an explosive mixture which needs only a spark or flame to set it off. This solves the mystery of those few instances wherein film seems to explode: it is the gas produced by the partial combustion of film that explodes. Effect of Emulsion on Film Combustion Up to this point only the flammable properties of pure celluloid have been discussed. Motion picture film has, in addition to the celluloid base, a coating of gelatin which serves to carry the black finely-divided silver particles which make up the soundtrack and picture image. The presence of this emulsion considerably modifies the burning. In the first place, the emulsion slows the combustion of the film base, rendering the fire less violent and increasing the concentration of explosive, poisonous celluloid gases. Second, whereas pure celluloid leaves little or no ash when it burns, the emulsion of coated film carbonizes to form a voluminous black ash which, of course, contains all the metallic silver of triefilm. When film burns in the projector^ decomposition products of the gelatin, deposit as a tar upon the relatively cool metal parts. Thirdly, the emulsion contributes a. dense smoke to the colorless (invisible) gases produced by the burning celluloid. Of the celluloid degradation gases themselves, only carbon monoxide is a deadly posion; the others are deleterious by reason of their suffocating nature. The choking fumes of the smoldering gelatin contain appreciable quantities of am(Continued on page 25 ) SMPE-ACADEMY TEST REELS AVAILABLE Code Length Test Film No. (in Feet) Price 35-Mm Visual Test Film VTF-1 450 $ 17.50 Focus-andAlignment Section VTF-FAS 100 5.00 Travel-Ghost Target Section VTF-TGS 100 5.00 Jump-andWeave Target Section VTF-JWS 100 5,00 35-Mm Theater Sound Test Film ASTR-3 500 17.50 35-Mm Multifrequency Test Film Type A — Laboratory Type APFA-1 450 25.00 Type B — Service Type ASFA-1 300 17.50 35-Mm Transmission Test Film TA-1 250 17.50 35-Mm Buzz-Track Test Film ABZT-1 50 min* 0.04/ft 35-Mm Scanning-Beam Illumination Test Film Type A — 17 Position Track A1TP-1 230 12.50 Type B — Snake Track AST8-1 8 0.50 35-Mm Sound-Focusing Test Film Type A— 9000-Cycle Track A9KC-1 50 min 0.035/ft Type B— 7000-Cycle Track (Area) A7KC-1 50 min 0.035/ft Type C— 7000-Cycle Track (Den sity) D7KC-1 50 min 0.035/ft Type C — Acetate Base D7KCS-1 50 min 0.04/ft 35-Mm 3000-Cycle Flutter Test Film A3KC-1 50 min 0.05/ft 35-Mm 1000-Cycle Balancing Test Film For Two Machines ABL2-1 14 0.50 For Three Machines ABL3-1 21 0.75 1000-Cycle Test Film ABLN-1 50 min 0.035/ft 35-Mm Multifrequency Warble Test Film APWA-1 450 25.00 16-Mm Sound-Projector Test Film Z52.2 200 12.50 16-Mm Multifrequency Test Film Z22.44 150 41.25 16-Mm Buzz-Track Test Film Z52.10 100 27.50 16-Mm Scanning-Beam Illumination Test Film Laboratory Type Z52.7-L 100 27.50 Service Type Z52.7-S 100 27.50 16-Mm Sound-Focusing Test Film Laboratory Type Z22.42-7000 100 27.50 Service Type Z22.42-5000 100 27.50 16-Mm 3000-Cycle Flutter Test Film Z22.43 380 104.50 16-Mm 400Cycle Signal-Level Test Film Z22.45 100 27.50 Minimum. INTERNATIONAL PROJECTIONIST • February 194ft