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.
April, 1930] TESTING FOR SODIUM TniOSULFATE 421
indicates the presence of any reducing agent whether it be sodium thiosulfate or not, but this error is also common to the three abovementioned methods.
The use of mercuric chloride, however, has several distinct advantages as follows: (1) Only a relatively small quantity of the film or print is required for testing; (2) the test can be made very quickly; (3) it probably indicates the presence of a reducing agent more satisfactorily than the other methods inasmuch as mercuric chloride causes the silver image to be bleached and thus liberates any adsorbed insoluble thiosulfate compounds which might be associated with the silver; and (4) it is extremely delicate and capable of detecting the presence of 0.05 milligram of sodium thiosulfate (crystals) .
The Test Solution. — Although a plain solution of mercuric chloride gave good results, the following formula containing potassium bromide was more sensitive:
Metric . Avoirdupois
Mercuric chloride 25 grams 365 grains
Potassium bromide 25 grams 365 grains
Water to make 1 liter 32 ounces
Method of Testing. — Two methods of .testing the thoroughness of washing of photographic materials are possible, as follows:
(a) By determination of the absolute quantity of hypo in the film.
Data on the hypo content of photographic films are of little value unless they are accompanied by data giving the quantity of hypo necessary to cause fading or otherwise impair the image. Such data are outlined below.
The absolute hypo content of the film may be determined as follows: Place 10 cc. of the mercuric chloride solutions in each of a series of small, glass cylinders. Place a single frame of motion picture film cut into small pieces in one of the cylinders, and then add increasing quantities of a 1:1000 solution of hypo to each of the remaining cylinders containing the test solution. Allow them to stand for 15 minutes, stirring the film occasionally with a glass rod, and compare the opalescence of the solutions. The quantity of hypo in the cylinder whose opalescence corresponds with that containing the film is equal to the quantity of hypo in the film strip.
(b) By comparison of the test film with films which have been washed for known safe periods.