Motography (1912)

220 MOTOGRAPHY Vol. VIII, No. 6. Testing Kinematograph Films THE great development of the kinematograph industry in France and the excellence of French films are largely due to the application of systematic tests, which are very often neglected in Germany and other countries, says Dr. Gustave Bouwitt in Zcitschrift fuer Angewandte Chemice. Most of the celluloid films used in ordinary photography are sliced or planed from celluloid blocks and are consequently hard and dry from the beginning. Kinematograph films, on the contrary, are made by pouring a celluloid solution upon a moving base in a continuously operating machine, and they acquire the necessary solidity by a process of slow drying. If this process is not carried far enough the film continues to dry and shrink during use and soon becomes torn and worthless. Undried or imperfectly dried films made by this method also show a tendency to curl toward the "dry" side (i. e., the side which is not in contact with the temporary base) in the machine. Such films do not lie flat in the gate of the projecting lantern and their curvature produces distortion in the picture and causes the film to wear out more rapidly. Sensitized kinematograph films are sometimes injured by electric sparks produced by reeling the film too tightly in a moist condition or in a damp atmosphere. What are the requirements which should be satisfied by a good kinematograph film? In the first place, the film should be both flexible and hard enough to be used for 1,000 to 1,500 projections. The gelatine coating should remain firmly attached to the celluloid without having its photographic properties affected by the latter even after long keeping. The celluloid foundation should not change in form or dimensions in the dry or wet state, the film should show no dust or other impurities under 200-fold magnification, and its surface should not be easily affected by scratches or other mechanical injuries. The photographic emulsion of a negative film should be very sensitive and free from fog. The latter quality is likewise necessary in the positive film, which should be capable of yielding fine-grained black pictures, rich in contrast. The testing should include, in the first place, the dimensions of the film. The total thickness, inclusive of the emulsion, should be from 0.11 to 0.16 millimeter (0.004 to 0.006 inch), the width 34.8 to 35.0 millimeters (1.37 to 1.38 inch). The height of the picture was fixed at either three-fourths or four-fifths the width, by the International Congress held in Paris in 1900. Hence the height of the picture should be about 18 millimeters (0.7 inch) and its width 24 millimeters (0.95 inch), leaving 5.5 millimeters (0.22 inch) for the perforations on each side. The interval between consecutive pictures is 1 millimeter (0.04 inch). Accuracy in the width of the film is particularly important, because too wide a film will stick in the gate, the width of which is 35.1 millimeter (1.382 inch), or will pass through it by jerks, while too narrow a film will produce unsteadiness by lateral oscillations. The shrinkage, due to gradual evaporation of cellulose solvents from an imperfectly dried film, should not exceed 1.25 per cent in six months, and is determined by measuring the length of a strip of film at regular intervals during that period. Another cause of variation in the length of a gelatine-coated film, in the moist state, is found in the hygroscopic properties of the gelatine and also of the foundation when the latter has been subjected to a process of saponification for the purpose of making the coating adhere firmly. The foundation itself, especially if it is composed of acetyl-cellulose, is not always waterproof. The amount of stretching due to these causes is determined by attaching a weight of 200 grammes (about 7 ounces) to one end of a strip of film and suspending the strip by the other end in water. The increase produced by six hours' immersion should not exceed 1.25 per cent. Other changes caused by water are studied by soaking the film and carefully examining it. In addition to celluloid and acetyl-cellulose, various other substances, including viscose, formyl-cellulose and hardened gelatine, are sometimes employed as the material of film foundations. As these films are not waterproof they are coated, on both sides, with celluloid or acetyl-cellulose, but water 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 DO 00 00 00 GO 00 00 00 00 00 Tests of Kinematograph Films for Regularity of Perforation. The Upper Diagram Indicates Poor, the Lower One Good Perforation. can still be absorbed at the unprotected edges and perforations, causing swelling and deformation. The tensile strength and extensibility of a film are measured by the usual methods. The strength ranges from 5 to 7 kilogrammes per square millimeter (7,000 to 10,000 pounds per square inch) for a film of 0.1 millimeter (0.004 inch) thick. The extensibility varies from 10 to 15 per cent. The flexibility is measured by a machine which bends the film in opposite directions alternately. The film should also be tested in the conditions of practical use. For this purpose an endless band of film is run through the kinematograph at a known speed for a measured interval of time, so that the number of times it has passed through the machine can be computed. A good celluloid film should suffer little damage from 1,000 or 1,500 passages. The gelatine coating of a good kinematographic film adheres so firmly that it cannot be detached, even partially, by pinching, pulling or rubbing. The inflammability is tested by exposing a motionless film, in the gate of the kinematograph, to the rays of the projecting lantern. If the film is blank it should not