International projectionist (Jan-Dec 1950)

hence varies greatly. An ample supply of air facilitates the combustion, thus increasing the temperature; and, naturally, a large mass of burning film makes a hotter fire than a small mass of film. A temperature in excess of 2,000° C. (3,600° F.) is probably produced when a 2,000-foot reel of film burns in a projector magazine. The production of heat amounts to approximately 18,000,000 gram-calories.5 A 2,000-foot roll of film requires from 20 seconds to about a minute to burn up completely, depending on the conditions. A blazing reel of film in a projector magazine is beyond control in about 5 seconds from the time of ignition; and it burns for about 45 seconds in the case of a 1,000-foot reel, and about 1 minute in the case of a 2,000-foot reel. Analyses of Gases Evolved It is difficult to give an exact analysis of the gases produced by burning nitrate film base. The presence of gelatine emulsion and the amount of air available have a profound influence upon the composition of the resulting fumes. But in every case the fumes are explosively combustible and poisonous. When blank emulsion-free celluloid film burns in the total absence of air, the following analysis is obtained: % by Volume Carbon dioxide 14 Carbon monoxide 47 Hydrogen 18. Methane 15 Nitrogen oxides 1 Nitrogen 5 But if the film be unwound in a loose pile and burned with access to plenty of air, the analysis is somewhat as follows: % by Volume Carbon dioxide 55 Carbon monoxide 18 Hydrogen 2 Methane 8 Nitrogen oxides 15 Nitrogen 2 And rolls of film burning with only a moderate supply of oxygen give the following analysis: % by Volume Carbon dioxide 35 Carbon monoxide 40 Hydrogen 3 Methane 10 Nitrogen oxides 9 Nitrogen 2 Sulfur dioxide 1 Effect of Various Gases The last of these analyses is especially important because it expresses the proportions of gaseous products arising 5 This corresponds to 1,800 kilogram-calories, or about 7,150 British thermal units per pound (200 feet) of film. from the combustion of emulsion-coated film under average conditions. It can be seen from these analyses that three combustible gases (carbon monoxide, hydrogen, and methane) and two highly poisonous products (carbon monoxide and such oxides of nitrogen as the dioxide and tetroxide) are generated. The combustible constituents render the gas of burning nitrate film explosive when mixed with air within rather wide limits. As a rule, any mixture of from 9% to 40% of the celluloid gases in air constitutes an explosive mixture which requires only a spark or flame to set it off. As far as the poisonous gases are concerned, the nitrogen dioxide-tetroxide system is the most important. True, carbon monoxide will most certainly kill if breathed for a sufficient length of time, and even the non-poisonous constituents can cause death by suffocation ; ANSWER TO YOUR TECHNICAL PROBLEMS . . . The Altec Service Man and the organization behind him 161 Sixth Avenue, New York 13, N. Y. PROTECTING THE THEATRE— FIRST PLACE IN ENTERTAINMENT MANUFACTURERS OF: Projectors, Sound Heads, Bases, Magazines, Sound Systems, Replacement Parts, Accessories, etc. Wenzel Presents . . . SOUND HEAD WSH-3 Send for complete descriptive circulars, giving full details of the many advantages of this new WENZEL product. WENZEL PROJECTOR CO. 2505-19 S. Chicago State St. 16, III. INTERNATIONAL PROJECTIONIST • February 1950 33