We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
June, 1930] STOP BATHS AND FlXING BATHS 683
2.5 per cent solution of sulfuric acid.* The acid was added slowly until the solution was just acid to the indicator. The number of cubic centimeters required multiplied by 3.8 gives the number of cubic centimeters of concentrated acid to add per gallon.
It is absolutely essential that the following procedure be adopted when the bath is revived with sulfuric acid in order to prevent sulfurization. The sulfuric acid should be diluted by pouring one part (by volume) of the concentrated acid into ten parts of water. Then cool to 70° F. and add slowly to the cooled fixing bath while stirring the latter rapidly. The acidity of the fixing bath should be tested before all the acid is added so as to be sure that the quantity of sulfuric acid has been determined accurately. If the bath is to be used immediately after revival enough sulfuric acid can be added to bring the acidity to a pH of 3.0; otherwise the bath should not be revived until ready for use. Although the addition of sulfuric acid to fixing baths increases their tendency to sulfurize, none of the baths in the exhaustion tests sulfur ized in less than one week at 70°F.
The quantity of acid which it is necessary to add at each revival point and the number of feet of film which can be processed before revival depends upon the quantity of developer retained by the film and the alkalinity of the developer. With the apparatus used in this investigation 100 feet of motion picture positive film developed in D-16 carries into 1 gallon of fixing bath 5 per cent of D-16. One hundred feet of panchromatic negative film developed in D-76 transfers 6.5 per cent of D-76 per gallon of fixing bath. The results of the exhaustion tests indicate that with positive film developed in D-16 developer, and without rinsing,'the fixing bath should be revived every 75 feet per gallon, and with negative film developed in D-76 developer the bath should be revived every 50 feet per gallon if uniform hardening properties are to be obtained. An increase in the number of feet of film per gallon which can be processed before revival is necessary can be obtained by rinsing the film in water after development.
(5) Revival of Hardening Properties by Addition of Chrome Alum. — Preliminary experiments were made to determine the effect of adding further quantities of chrome alum to fixing bath No. I which had been exhausted with respect to its hardening properties. The addition of
* The acid solution contained 2.5 cc. of pure concentrated sulfuric acid per 100 cc. of solution. This concentration was chosen so that 1 cc. per 25 cc. of fixing bath would be equal to 1 cc. of concentrated acid per liter.