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June, 1930] STOP BATHS AND FlXING BATHS 677
bath, without rinsing, for five minutes, washed twenty minutes and the melting points determined. Similarly, strips of Eastman panchromatic negative motion picture film were developed for ten minutes in D-76 developer, fixed for ten minutes, washed for twenty minutes, and the melting points determined.
The acidity of the various solutions was determined by a colorimetric method using indicators, as described in Part I of this paper.
Fig. 1 shows the effect of the addition of D-16 developer on the hardening properties of fixing bath No. I from which it is seen that:
(a) The hardening action and the acidity of the fresh bath gradually decreased as the quantity of developer added increased, and the degree of hardening was not satisfactory after a quantity of developer had been added equal to 7.5 per cent of the volume of the bath. This corresponds to 150 feet of unrinsed motion picture positive film per gallon which may be considered as the life of the fresh bath.
(b) After standing four days at 70°F. the life of the bath was reduced to 100 feet of film per gallon and after two weeks at 70° F. to 75 feet per gallon.
(c) The hardening action of the solutions stored at 70°F. was similar to that of solutions stored at 110°F. until the latter sulfurized.
(d) A minimum degree of hardening was obtained after the solutions had been stored two weeks at 110°F.
(e) The acidity of the solutions containing 2.5 per cent and 5 per cent of D-16 increased on standing.
(/) The hardening properties of the solutions whose pH value was greater than 4.0 decreased on ageing, which indicates that the pH of the bath should always be maintained at a value less than 4.0 in order to obtain uniform hardening properties.
The hardening properties of fixing bath No. I diminished more rapidly on the addition of a definite volume of D-76 than was the case with D-16. With D-76 at 70°F. the life is about 100 feet of unrinsed motion picture negative film per gallon of fresh fixing bath but when four days old this is reduced to 60 feet per gallon. The life on storage at 110°F. was of the same order.
(2) Effect of the Addition of Sodium Sulfite and Sodium Carbonate on Hardening Properties. — The following table indicates the relative effect of sodium sulfite and sodium carbonate when added to the fixing bath. The hardening tests were made with positive film developed in D-16 at 70°F., the samples being stored at 110°F.