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.
486 J. I. CRABTREE AND H. D. RUSSELL [J. S. M. p. E.
acid appears to be the most suitable available acid for non-hardening baths because it does not materially affect the hardening properties of a potassium alum fixing bath and has a minimum tendency to precipitate sulfur therein. Of the common acid salts which can be used for this purpose, sodium bisulfite is perhaps the most suitable since it does not impair the properties of the fixing bath and, so far as is known, will not blister the film under normal conditions.
Of the available hardening agents for use in acid hardening stop baths, chrome alum was considered the most promising because it is capable of producing a greater degree of hardening than potassium alum and is therefore suitable for use at high temperatures, under which conditions the use of a hardening stop bath is usually desirable. Both acetic and sulfuric acids were tested to determine their suitability for use in acid hardening baths.
Hardening Action of Chrome Alum Solutions. — In the preliminary experiments, the hardening action of chrome alum solutions on both neutral and alkaline film was investigated. The most alkaline film met with in actual practice was that placed directly from the developer into the stop bath without rinsing. The neutral film was rinsed for fifteen minutes after development and before placing in the chrome alum bath, which rendered it less alkaline than any met with in actual practice. In making the hardening tests, strips of motion picture positive film were developed for five minutes in D-16* at 70°F., rinsed for fifteen minutes (neutral film) and then agitated in the chrome alum bath every thirty seconds for three minutes. For the alkaline film tests the rinse was omitted. On leaving the bath, the film was again rinsed for fifteen minutes, fixed in a plain 30 per cent hypo solution for five minutes, washed for twenty minutes, and the hardening determined as in the case of fixing baths.1 The acidity of the solution was determined in the following manner:
* Formula
D-16
Metric
Avoirdupois
Elon
0.3 gram
2 ounces
Sodium sulfite (desiccated)
40 . 0 grams
16x/2 pounds
Hydroquinone
6 . 0 grams
2*/2 pounds
Sodium carbonate (desiccated)
19.0 grams
73/4 pounds
Potassium bromide
0 . 9 gram
58/4 ounces
Citric acid
0.7 gram
4Y2 ounces
Potassium metabisulfite
1 . 5 grams
10 ounces
Water to make
1 liter
50 gallons
Average time of development: 5 to 10 minutes at 65 °F. (18 °C.).