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Fixing Baths — Crdbtree and Hart 381
of sulfite in the other case necessary to precipitate aluminium sulfite in the case of typical formulas. The formulas tested were so chosen that the sulfurization life was equal in all cases. The followingtable gives the results of these experiments.
Table III
The Relative Effect of Developer (MQ^J a7id Sodinm Sulfite on the Precipitation of Aluminium Sulfite in a Fixing Bath
Composition of Bath
$
<;i
^
S
S
^
-1
§
2;
•5^
0
% Sod.
Sulfite
% MQ25 to
Ratio MQ2-,
c
^
^
to Cause Precip.
Cause Precip.
Sod.
Sulfite
1
2Q
^
tq
70°F.
115°F.
70''F.
115°F.
70°F.
11S°F.
^
^
^
^
1.
4.6
1.0
30
7
6.5
7.0
1.5
1.2
1.5
30
2.
5.5
2.6
36
20
6.6
7.7
1.5
3.0
1.6
30
3.
. 2.4
1.4
15
8
6.3
5.7
1.0
1.0
1.5
30
4.
5.5
5.1
40
34
8.0
6.7
0.5
1.5
3.0
30
5.
1.7
3.8
14
22 Average
8.2 7.1
5.8 6.6
3.0
2.6
3.0
30
These results show that although the relation is not constant the results are sufficiently uniform to permit their use in determining the relative developer capacity from the curves in Figs. 4 and 5. It is considered that the ratio of approximately 1 :6 is permissible ; that is, for 1.0% sodium sulfite which may be added to a given formula before precipitation of aluminium sulfite occurs 6.0% of MQ2g developer may be added before a similar precipitate will be formed. In applying these results to developers other than MQ25 it is necessary to know the alkali and sulfite content of the developer in relation to that of the MQ25 developer.
From the curves (Figs. 4 and 5) it is seen that (a) for equal concentrations of alum and acid the developer capacity decreases with an increased quantity of sulfite; (b) for equal quantities of sulfite and alum the developer capacity increases as the concentration of acetic acid increases; (c) for equal quantities of sulfite and acid the developer capacity is only slightly affected by an increased concentration of alum.