The international photographer (Jan-Dec 1933)

May, 193S The INTERNATIONAL PHOTOGRAPHER Forty-three proximity of the washing tanks are sufficient to maintain the temperature below 68°F. When the temperature is allowed to exceed 70°F., the grain of the film increases and sulfur dioxide may be released. The motion of the film through the solution causes sufficient agitation for proper fixing. The strength of the fixing bath is checked by noting the point in the machine at which the film becomes clear. When this point approaches the vicinity of the wash tanks, the solution is strengthened by replacing some of it with fresh solution. The average time of fixing negative film varies from 8 to 12 minutes. Several minutes less are sufficient for fixing positives. E. WASHING Wash water is usually obtained directly from the main supply. In some instances during warm seasons, some rough method of cooling may be required. Normally, however, the temperature of the tap water does not exceed 70°F., which is satisfactory for washing. The water flows continuously from the main into the wash tanks, and thence to the drain. A chemical test is frequently employed to determine whether the film has been sufficiently washed. The drippings from the film can easily be tested for the presence of hypo by adding a solution of potassium carbonate and potassium permanganate in water. A greenish yellow color results when hypo is present. The average time of washing negative film varies from 10 to 15 minutes. Several minutes less of washing are sufficient for positive film. F. DRYING Since the universal adoption of machine methods of developing film, the drum method of drying is no longer used. By the modern methods, film is dried in cabinets through which conditioned air circulates. The relative humidity of the air is maintained at approximately 40 per cent, at a temperature of about 73°F. In some instances, when the machines are required to operate at maximum capacity, temperatures as high as 110 °F. are necessary in order to be sure that the film becomes sufficiently dry. However, it is considered poor practice to operate under such conditions, 85°F. being supposedly the optimal temperature for drying. The rate of flow of air required for complete drying depends upon the construction of the cabinets, the posi tion of the baffles, and other variables. An operator constantly checks the drying of the film by inspecting the curl of the film through the glass doors of the drying cabinets. G. CONDITIONING Laboratories have found it necessary during the last few years to be equipped with high-grade air conditioning systems. All dust particles must be removed from the air admit ted to the developing, printing, and assembling rooms, and particularly from the air forced through the drying cabinets. The temperature and humidity of the air in the drying cabinets are also maintained constant. Automatic temperature and humidity controls are installed in order to maintain the proper drying conditions regardless of the exterior atmospheric conditions. (Continued on Page 47) EVERYTHING PHOTOGRAPHIC for Professional and Amateur New and used. Bought, sold, rented and repaired. Camera Silencing. Send for Bargain Catalogue Hollywood Camera Exchange 1600 Cahuenga Blvd", Hollywood Tel; CL 2507 . HO 9431 Cable Address: HOcame* Open 8 a. m. to 10 p. m. Please mention The International Photographer when corresponding with advertisers.