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k62
BRITISH KINEMATOGRAPHY
Vol. 21, NO. 3
This point is determined by the nature of the film under test.
Tests carried out on 35 mm. film showed that nitrate film would continue to burn over 21 in. of the perimeter of a 14 in. diameter semicircle, whereas safety film burnt up to a length of 16 in. on the perimeter. The relative flammability of safety film and other materials in the same form could be assessed from the length to which each material continued to burn.
The distance of flame spread for any one specimen in these preliminary tests was generally greater when the emulsion was upwards and so in all subsequent tests the film specimens were mounted in this way.
Apparatus and Experimental Procedure for 35 mm. Film Tests
The apparatus on which the tests on
35 mm. film were carried out is shown in Fig. 1. Two steel supports in the form of a 14 in. diameter semicircle were mounted on a steel base, with their adjacent edges 1 in. apart. One support was graduated at inch and half-inch intervals over a length of 21 in. A copper cup 1 cm. by 2 cm. by 0.3 cm. was mounted on an insulating base between the two supports at one end of the semicircle. A 21 in. length of film was held in position over the supports by means of two thin steel strips.
The test was carried out as follows : 0.3 c.c. of absolute alcohol were introduced into the copper cup and ignited. The distance over which the film burnt was noted.
Six specimens of each type of film were tested in this way and the mean distance of spread for each is shown in Table 1.
Table I
Distance of Spread of Flame on 35 mm. Safety Film
Specimen
Thickness in. x 103
Mean distance of flame spread in.
A. Base
5.3
Film did not continue to burn after the alcohol flame had burnt out.
A. Emulsion coated
5.9
12
A. Processed
5.8
Film did not continue to burn after the alcohol flame had burnt out.
B. Base
5.7
5
B. Emulsion coated
5.9
11
B. Processed
5.8
11.5
C. Base
5.3
11
C. Emulsion coated
5.7
12.5
C. Processed
5.7
12.5
D. Base
5.4
Film did not continue to burn after the alcohol flame had burnt out.
D. Emulsion coated
5.9
Film did not continue to burn after the alcohol flame had burnt out.
D. Processed
5.9
Film did not continue to burn after the alcohol flame had burnt out.
E. Base
5.3
5
E. Emulsion coated
5.5
13.5