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May, 1930]
STOP BATHS AND FIXING BATHS
499
greatest importance because, although a film is insoluble in boiling water, it may reticulate readily and a reticulated film is usually worthless.
In practice when processing at high temperatures it is important that the film should not swell and at the same time it should have a fairly high melting point. In many cases, the thickness of the film was measured before determining the reticulation and melting points and it was found that a fairly close relation existed between the degree of swelling and the reticulation point as is shown by Table II.
TABLE II. Relation between Hardness and Degree of Swelling of Film
Footage Processed per Gallon
Thickness
Reticulation Point
Melting Point
0
0.010 in.
Nil
210 °F.
125
0.011 in.
Nil
210 °F.
190 (before revival with acid)
0 . 013 in.
105 °F.
170 °F.
190 (after revival with acid)
0.013 in.
105 °F.
170 °F.
250
0.013 in.
100 °F.
130 °F.
315 (before revival with acid)
0.013 in.
95 °F.
120 °F.
315 (after revival with acid)
0.013 in.
95 °F.
120 °F.
375
0.013 in.
95 °F.
110°F.
It is seen that the unswollen film did not reticulate but, after swelling from 0.010 to 0.013 inch, the reticulation point dropped to 105°F., although the film melted at a temperature as high as 170° F.
The effect of adding D-16 developer to a 2 per cent chrome alum stop bath is shown in Fig. 7. The results indicate that a quantity of developer equal to 10 per cent of the volume of the bath may be added before an immediate drop in the melting point occurs. This corresponds to a footage of 200 feet per gallon. After storage for three weeks at 70°F. and 110°F., the life of the bath was reduced to 150 feet per gallon. The hardening action of a similar stop bath containing D-76 developer fell off more rapidly with the addition of increasing quantities of developer. This was to be expected as formula D-76 contains more sodium sulfite than formula D-16. The life of the bath with D-76 developer was reduced to 115 feet per gallon in the fresh bath and to 85 feet per gallon after the bath had stood for three weeks.
From the results in Fig. 7 it is seen that: (1) a change in the storage temperature from 70°F. to 110°F. has very little effect on the loss in hardening properties on the addition of developer;