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The winding oi film involves a constant danger of scratching, and old hands even maintain that films are more often scratched in winding than in projecting. As regards the relative merits of vertical and horizontal rollers both work quite well, but in unpractised hands the horizontal winder is undoubtedly to be preferred, as there is far less risk of the outer coils falling and thereby scratching the film. In this form of roller, too, the two spools are more easily aligned, so that the film will not overlap the spool edges. The spindles, especially the take-up spindle should be as large as possible as there is far more risk of scratching from a small spindle.
In connection with feed and take-up we must repeat our earlier warning against leaving unwound film upon the table or letting it fall on the floor. Further, regular braking is an important factor, if scratch is to be avoided. It is a mistake to take in the film quite loosely and then suddenly draw it tight by pulling at the free end; this will scratch the film. On the other hand, it is also wrong to " brake " the film when rolling so much that it becomes scratched by friction with gritty fingers, etc. The brake must be put on just as much as is necessary to wind the film up tightly without its getting scratched.
In order that film may last, it is very important to secure good joins. Copies shown in schools will mostly be joined in the copying studio and we need therefore make only a passing reference to the rules for ensuring proper joining. The perforations of the two pieces of film must fit into the teeth of the joining apparatus with mathematical exactness, so as to cause no break in the regularity of the holes. Otherwise the sprocket-teeth will no longer exactly take the perforations and the holes will lose their shape. The margin of difference between the perforations and the sprocket-teeth is less than 0,01 millimetres, so that the very slightest irregularity will spoil the holes. For the rest, every joiner has instructions issued with it, and these should be exactly followed. It should only be added that most film glue is highly combustible, which necessitates caution in the matter of smoking and the use of naked flames.
The difficulties attendant upon the preservation of celluloid film described ■ earl}/ in this article do not apply at all to what is known as safety-film, which, instead of the ester of cellulose and nitric acid, contains the ester of cellulose and acetic acid. This film is completely safe, is recognized as such by all authorities and has, of course, for years been recommended for use in amateur cinematography. No special regulations are needed for its storage. In Germany a Bill has been framed by which all films of less than 34,9 mm. width must be made on a safety foundation. If this becomes law, it will mean that projections of 16 mm. film will no longer be subject to police supervision and that substandard films can be shown at any time and in any place before any number of people. The Bill prescribes that substandard films must be comparatively uninflammable and incombustible. In order to reach an exact definition of inflammability, the use of a specially