CH. XII DANGER OF FIRE 431 



DANGER OF FIRE 



596. Before the introduction of non-inflammable films, all 

 films were made by coating the emulsion upon celluloid. This is a 

 nitrate (the trinitrate) of cellulose to which is added a certain 

 amount of camphor. A more highly nitrated cellulose is called gun 

 cotton. 



There is sufficient oxygen in the nitrated cellulose to partially 

 support combustion and it is the cause of the highly inflammable 

 nature of celluloid. This was strikingly shown in some experi- 

 ments made to ascertain the possible danger from an ignited film. 

 A small reel of film was lighted and put under a tin box so that no 

 air could get at it. A fire in ordinary combustibles, such as paper 

 or wood, would soon be smothered, but the roll of film continued 

 to decompose in the closed box. This shows that if a roll of film, 

 even in a closed fire proof magazine, once catches fire it will con- 

 tinue to burn as long as there is anything left of it. 



The gases given off from the film decomposing in a closed box are 

 very disagreeable and will burn in contact with air if they are once 

 lighted. If celluloid will burn so vigorously in a closed box, what 

 would be the effect of a large reel of film lying uncoiled in a waste 

 basket or on the floor should it once catch fire ? This was the prac- 

 tise in the early days of the art of projecting moving pictures. 

 Seven to ten meters (twenty or thirty feet) of film piled loosely, will 

 be completely consumed in a few seconds, burning with a fierce 

 flair e while it lasts. 



In view of this very evident danger, modern, apparatus is 

 designed to make it as safe as possible. To the good design of the 

 machine must be added the cooperation of the operator to prevent 

 a fire. 



The fire shutter (fig. 228), automatically closes whenever the 

 machine is not running. This shutter is placed in front of the film 

 and prevents the light of the arc from striking it except when it 

 is in motion. If the film should break, however, a tag end might 

 remain in the aperture plate and be ignited, the fire shutter remain- 

 ing open while the crank was being turned. To prevent this 

 trouble the light should be instantly shut off whenever a film 

 breaks. 



