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402 Transactions of S.M.P.E., Vol. XIII, No. 38, 1929
minutes in the first bath. Also, if the hardening properties of the first bath are impaired because of exhaustion, adequate hardening is produced in the second fresh bath. However, any stains or diehroic fog produced in the first bath are not removed in the second so that it is important to maintain the first one acid and agitate the film sufficiently on first immersion.
Fixing Bath Troubles
A. Sludging of the Fixing Bath : A fixing bath may turn milky immediately on adding the hardener, or after being in use for some time. The milkiness may be of two kinds :
1. If the precipitation is pale yellow and settles very slowly on standing, it consists of sulfur and may be caused by :
(a) Too much acid in the hardener.
(b) Too little sulfite or the use of impure sulfite, in which case there is not sufficient present to protect the hypo from the acid. Loss of sulfite also occurs through oxidation if the hardener is stored in an open crock. The surface of the liquid should be protected from the air by a floating cover of Kodaloid or preferably the hardener should be stored in an air-tight vessel.
(c) High temperature. The hardener should only be added to the hypo solution when at room temperature. If the temperature of the acid fixing bath is over 85° F., it will not remain clear longer than a few days even when mixed correctly. The only remedy is to throAv the sulfurized bath away and mix fresh solution as required.
If a sulfurized bath is used, the sulfur is apt to be precipitated in the gelatin, and later may cause fading of the image.^
2. If the precipitate is white and disappears on standing for a few hours, and a gelatinous sludge of aluminium sulfite settles out. it may be caused by :
(a) Too little acid in the hardener. For example, supposing a formula calls for pure glacial acetic acid and 28% acid is used by mistake, then less than one-third the required amount has been added.
(b) Too little hardener in the fixing bath. Also, a fixing bath with the correct proportion of hardener, when exhausted, still contains alum and sulfite but no acid, and these combine to form a sludge of aluminium sulfite.