The Bioscope (Jul-Sep 1931)

iv THE BIOSCOPE warm -when inspected within ten minutes after the fire. Wooden Dowels not Strong Enough A further test was made by exploding a mixture of the decomposition gases and air in the sheet-metal chamber at the back of the cabinet by the use of automobile spark plugs. On the first trial one side was blown off from the wooden cabinet because the wooden dowels used to fasten it in place did not secure it sufficiently well. Parts of the cabinet made from ordinary oak were burned in the fire which followed the explosion, but other parts constructed of chemically fireproofed oak did not flame or glow after the flame from the burning material was removed. A second cabinet constructed with bolts to hold the woodwork in place was tested in a similar manner by exploding the gases given off during the decomposition of three 1,000 ft. rolls of motion picture film. Cheap Metal Cans Best In this case the cabinet held together though the sheet-metal was bulged on the sides. Several rolls of film in drawers adjacent to those where decomposition took place were unharmed. Some of the latter rolls were contained in fibre boxes and others in light weight tin-plate containers. Inasmuch as no appreciable amount of heat reached this point the insulating properties of the fibre box were of no advantage and it was concluded that cheap metal cans, such as used by film manufacturers as containers for raw film, would be satisfactory from this point of view. Conclusions from Fire Tests The above tests indicated that : — (1) Cabinet compartments can be insulated from each other by a f in. thickness of air MODERN CINEMA TECHNIQUE dried pine, but if the wood is not rendered fireproof it is ignited by the burning film and eventually the entire cabinet is consumed. (2) It is necessary to protect the wood from fire, either (a) by covering it with sheet metal completely or at least in all places exposed to flame during a fire, or (b) by treating the wood by impregnation with fire retarding chemicals so that it will not bum after it has been heated. (3) The fire retarding paint tested was found to give practically no protection to the wood. (4) If the outside of the cabinets or the chamber where they are housed must be protected by regular water sprinklers, the film should be covered in such a way that the water cannot reach it. The sheet metal drawers described give adequate protection. (5) Free vent must be afforded to gases arising from decomposition of the film, as otherwise there is danger of the gas pressure increasing until the container bursts. A committee of the Royal Photographic Society of Great Britain has recommended soldering the tin cans in which motion picture film is stored. This is an extremely dangerous procedure. Constructional details for a film storage cabinet are then given and for them direct reference to the original paper should be made. Particulars of a suitable type of vault for housing the cabinets are also given. Both negative and positive motion picture film should be given careful processing in the laboratory before placing in the storage vault. After fixing in the normal fixing bath it should be immersed again in a fresh hypo bath to insure thorough fixation. Washing should be thorough, the time required depending on the method employed, although August 12, 1931 from 45 minutes to one hour with suitable agitation of the film and adequate renewal of the wash water is usually sufficient. A final soak for 5 to 10 minutes in distilled water is also desirable. After drying thoroughly the film should be spooled on wooden cores (not on metal reels) , wrapped in chemically pure black paper of the type used by photographic manufacturers for packing unexposed motion picture film, and placed in ordinary tin plate cans. The tin plate or other rust resistant metal container is satisfactory provided it is inspected frequently. Importance of Moisture Content The moisture content of the film to be stored should preferably be such that it is in equilibrium with an atmosphere of 70 per cent, relative humidity at 75 deg. Fahr. before storing. Under these conditions no serious trouble will be encountered as a result of condensation of drops of moisture from the air in the can when the temperature is reduced to 45 deg. Fahr. If, for any reason, film must be cleaned before storing, use liquids which do not attack the film. Before exposing a roll of the cooled film to room conditions it should be warmed to a temperature above the dew point of the atmosphere so that moisture will not condense upon it when it is rewound. Moisture condensed on the film as dew would otherwise cause sticking of the film convolutions. A suitable warming cabinet maintained at a temperature of 75 deg. Fahr. to 80 deg. Fahr. and containing dry air should be located conveniently near the film vault. It is desirable to inspect all film by rewinding at least once every two years and if any signs of deterioration are visible a duplicate should be made. LARGE CUSTOMS DUTIES DON'T IMPROVE YOUR SOUND! BUY AN ALL BRITISH EQUIPMENT BUY THE BEST EQUIPMENT YOU CAN AND IT WILL BE AN F.l. EQUIPMENT FILM INDUSTRIES LT? LONDON FILM 60, WELBECK 2293 (2 . LINES) INDUSTRIES LIMITED, PADDINGTON STREET, W.1 Telegrams: TROOSOUND, BAKER, LONDON