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620 STANDARDS COMMITTEE [J. S. M. P. E.
to the positive type of core may never occur. However, the film manufacturers and some of the apparatus producers believe it would be of benefit to the trade if a single type of core could be used, and for that reason the single standard has been adopted.
(2) Sound-Track Dimensions. — A thorough study of the best dimensions for the 35 -mm. sound-track is being made by a committee of the Academy of Motion Picture Arts & Sciences. Our Committee is, therefore, waiting until the Academy committee has announced its findings before taking any action on this matter.
(3) 16-Mm. Sound-Film Sprocket. — A preliminary drawing has been given initial approval and has been sent out to the various members of the Standards Committee and to various manufacturers for criticism. The principles involved in handling singly perforated film are somewhat different from those used in handling doubly perforated film. For example, with 16-mm. sound-film, it is common practice to have the sprocket-teeth entirely fill the holes, at least in the lateral dimension, and guiding of the film in the picture gate by means of the sprocket-holes is almost universal. If such guiding is used, the sprocket-teeth must be rounded with a radius of curvature greater than that used for the film, or inevitably damage will result. It is the opinion of some that it is too early to standardize on sprockets for 16-mm. sound-film and that correct sprocket design depends entirely upon the design of the projector on which it is to be used.
(4) Definition of Safety Film. — The Standards Committee has given initial approval to the definition and specification of safety film recommended for adoption at a meeting of the International Standards Association at Berlin on June 28, 1938. Inasmuch as there are rather important differences of opinion with regard to the advisability of approving this definition, it is included herewith in full in order that we may have a fuller discussion :
Definition.
Safety film means a film that is slow-burning and difficult to ignite.
A film is called slow-burning if its burning time for a piece of film of 30 cm. takes more than 45 seconds . For films having a thickness of less than 0 .08 mm . , the burning time must be more than 30 seconds. The burning time is determined according to paragraph a.
A film is termed difficult to ignite if it does not ignite at 300 °C within 10 minutes.
Safety film must contain not more than 0.36 per cent of nitrate nitrogen.
Testing Method.
(a) Testing of Burning Time.