Military roentgenology / War Department.

Date:
[1944]
Catalogue details

Licence: Public Domain Mark

Credit: Military roentgenology / War Department. Source: Wellcome Collection.

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    the rate of water exchange, and the number of films having to be accommodated at any one time. Ordinarily, the rate of water exchange must be 4 to 8 times the capacity of the tank per hour in order to accomplish adequate washing of “screen” films within 30 minutes and “nonscreen”’ films within 1 hour. The quantity of wash water required and the efficiency of its washing are greatly enhanced with the use of a baffle design of wash tank and a cascade system of water flow, as provided with the U. S. Army Field Unit, Auxiliary Wash Section, (Item No. 96117) figure 57. With this design of wash tank, utilizmg a water exchange rate of 4 to 8 times the volume of its final wash compartment, approxi- mately 70 percent of the residual hypo is removed from the film emulsion in the first wash compartment —that located at the drain pipe position. After 5 minutes, the films should be removed from this compartment and placed in the middle compartment. Here, they are subjected to water contaminated less with the chemicals which are to be removed. The water of this compartment serves for washing against only approximately 30 percent of the residual hypo. The films should be removed from this compartment after another 5 minutes and placed into the freshest water. Thus, the freshest water serves to wash the emulsion after most of the residual hypo has been removed. On the basis of this cascade arrangement, the efficiency of washing is so increased that ordinarily practically all of the hypo can be removed from film emulsions within 15 to 20 minutes. Testing as to adequacy of washing can be accom- plished in a very simple manner. A single crystal of potassium permanganate may be dissolved in approximately 4 ounces of ordinary tap water. A light pink solution should be obtained. If the color be purplish red or a deep pink, more tap water should be added until a light pink color is obtained. Half of the volume should be kept in one beaker, as a control; the other half, used for the test. After what is believed to be adequate washing, the film should be raised from the wash water and _ its drippings allowed to fall into the light pink potasstum permanganate test solution. If these drippings pro- duce a discoloration of the pink, either to a yellow or a colorless solution, there is the evidence of residual hypo and inadequacy of washing. It must be realized that some tap water contains considerable organic constituents and that these could be responsible for fading of the pink color. Tap water rather than distilled water is suggested merely to simplify the procedure. However, when using tap water, it Is always important to check the control solution mentioned above. If that solution has retained Its light pink coloration, then discoloration in the test- ing solution can quite surely be attributed to residual hypo and inadequate washing. This procedure can be used to determine the proper time of washing required for any installation. f. Drying. After adequate washing of the films, they should be suspended for drying. This may be hastened with the aid of a draft of air such as provided with the U. S. Army Field Drying Unit, Item No. 96055. If the room temperature be not above 90° F., it may be practical to include use of the heater. However, if the air be too hot and the films too close to the heater, uneven drying might occur with resultant crinkling of the emulsion. g. In an average roentgenological department, approximately three-fourths of the film problems are attributable to errors incurred in the processing room. There, the possibilities are numerous as indicated by the tabulation of darkroom “don’ts.” (See app. I.)
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