432 



DANGER OF FIRE 



[CH. XI 



The time required for igniting a film was examined. It was 

 found that an ordinary film, partly black and partly transparent 

 when held in the condenser focus would first curl and later burst 

 into flame. The time required for each was noted, first with, then 

 without a water-cell. 



Image of arc 



No water-cell 

 Curl Burn 



With water-cell 

 Curl Burn 



20 Ampere D. C. Arc 



Concentrated spot 1.3 sec. 



vSmall spot 2 sec. 



24 Ampere A. C. 



Concentrated spot 6 sec. 



35 Ampere A. C. 



Spot large enough to project 



picture, film dead black ... 3 sec. 



2.6 sec. 

 3. 5 sec. 



5 sec. 

 7 sec. 



losec. 

 12 sec. 



losec. over 30 sec. 



1 2 sec. over 60 sec. 



With 3 5 amperes alternating current and the crater image large 

 enough to project the full size of picture, the film curled in 3 seconds 

 and burst into flame in 12 seconds. When a water-cell was used 

 the film was merely slightly warped and not in the least injured 

 after an indefinite exposure. With larger installations the water- 

 cell could not be relied on to protect the film indefinitely, though it 

 would much reduce the risk. 



The data given in 848 (fig. 342), shows the effects of the 

 water-cell in reducing the radiant energy. 



Examination was made of the probable security afforded by the 

 fire-trap of a fire-proof film magazine. A short piece of film was put 

 through the fire-trap of a film magazine. This fire-trap consists in 

 a flat tube, the lower end of which is nearly closed by a pair of 

 metal rollers. The flame would not follow the film through the 

 metal tube. When, however, the film was pulled rapidly through 

 the fire-trap it might or might not be extinguished by the rollers. 



With the upper magazine, where the film hangs down, the rising 

 flames heated the film to such an extent that when pulled upward 

 through the fire-trap it continued to burn on the other side. When 

 the film projecting from the lower magazine was ignited and pulled 

 down through the fire-trap, it was extinguished just as a strip of 



