American cinematographer (Feb-Dec 1929)

November. 1929 American Cinematographer Nine «.urves shown in Figs. 3, 4. and 5. it is seen that (a) for equal concentrations of alum and acid, the sulfurization life increases rapidly as the quantity of sulfite increases, the sulfurization life apparently increasing logarithmically with the concentration of sulfite; (b) for equal concentration of alum and sulfite, the sulfurization life decreases as the concentration of acid is increased; (c) for equal concentrations of acid and sulfite the sulfurization life decreases only slightly with increasing concentration of alum. 3. Factors Affecting the Developer Capacity — In order to determine the developer capacity (the quantity of developei which can be added to the fixing bath before precipitation of aluminium sulfite occurs) for all of the formulas represented by the various points in the curves shown in Figs. 3. 4. and 5, it would have been necessary to prepare a large quantity of these formulas and determine the quantity of developer necessary to precipitate aluminium sulfite in each case. It was considered desirable, therefore, to find a method whereby the curves already obtained could be interpreted in terms of "developer capacity." Curves 3, 4, and 5 show that with an increasing quantity of sulfite there is a tendency to precipitate aluminium sulfite, while with an insufficient quantity of sulfite, sulfur tends to precipitate. It is between these two limits that a suitable stable fixing bath exists; in other words, there is a definite quantity of sulfite which may be added to any given formula which is satisfactory with regard to sulfurization life before the precipitation of aluminium sulfite occurs. It was thought that it might be possible to find a definite relation between this quantity of sulfite and the quantity of developer which would cause similar precipitation. Experiments were therefore made to determine this relation by comparing the quantity of developer in one case, and the quantity 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 following table gives the results of these experiments: Table III The Relative Effect of Developer (MQ25) and Sodium Sulfite on the Precipitation of Aluminium Sulfite in a Fixing Bath — w._ ■o « 3 a a Composition of Bath ~ ■?. 5< g 0 3 c >> w ^3 $3 fi O m o t t i. -.4.6 1.0 30 7 6.5 7.0 1.5 1.2 1.5 30 ? 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 0 5.1 40 34 8.0 6.7 0.5 1.5 3.0 30 5. „_1.7 3.8 14 22 8.2 5.8 3.0 2.6 3.0 30 Average 7.1 6.6 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 MQ 25 developer may be added before a similar precipitate will be formed. In applying these results to developers other than MQ 25 it is necessary to know the alkali and sulfite content of the developer in relation to that of MQ-25 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. 4. The Application of Hardening Curves to the Fig. Preparation of Fixing Baths Having Required F-roperties. — From the curves (Figs. 3, 4 and 5) it is possible to compound a fixing bath having any given properties. The following three factors must be known before a suitable fixng bath may be compounded: (a) the hardening desired: (b) the developer capacity, and (c) the sulfurization life. With this information available, the series of curves (Figs. 3, 4, and 5) which gives the maximum hardening desired is selected and from these curves the necessary quantity of alum is determined. Then, by drawing a line parallel with the sodium sulfite axis at a distance from it representing the desired sulfurization life as indicated on the axis "life in days," and determining the limits of the sulfite content between the sulfurization and aluminium precipitation curves, the quantity of acid necessary is indicated by the curves whose sulfite limits correspond to one-sixth of the developer life desired. Then, by projecting the point of interesection of this parallell line and the sulfurization life curve to the sodium sulfite axis, the quantity of sulfite sufficient to give the necessary sulfurization life is indicated. This gives the complete hardening formula, which may be added to a quantity of hypo as determined by the amount of film to be fixed and the rate of fixation desired. 5. Example of Use of Curves in Compounding a Fixing Bath Formula — If it is desired to compound a fixing bath having the following properties: relative hardening 160°F.. sulfurization life 2 days (110°F.), developer capacity 6% MQ 25, proceed as follows: It is seen from Fig. 3 that the maximum hardening produced by an 0.5 % potassium alum solution with varying concentrations of sodium sulfite is approximately 160°F. Draw a line parallel with the sodium sulfite axis at a distance from it represented by two days on the sulfurization life curve at B and the aluminium precipitation curve at C. Project the points B and C to the sodium sulfite axis to the points E and F. respectively. The difference in the sodium sulfite concentration represented by these two points multiplied by 6 gives the relative developer capacity for the acidity (1.0%), which is represented by these curves; that is. .1.5% — 0.6%=0.9%: 0.9%X6=5.4% equivalent developer capacity. The quantity of sulfite represented by point E (0.6%) is the quantity necessary to give the desired (2 days) sulfurization life. This information gives the proportion of the various ingredients (0.5% potassium alum. 0.6 r/( sodium sulfite, 1.0% acetic acid) required to produce a fixing bath having the above desired properties. This hardener may then be added to a given hypo solution and the fixing bath is then complete. Fig. 3 was used for the above example merely for the purpose of simplicity. In order to compound fixing baths having properties other than the above it is necessary to refer to Figs. 4 and 5 or additional sets of curves for other concentrations of alum. In choosing the alum concentration, the minimum quantity which will give the necessary hardening is desirable. The quantity of sulfite to insure the necessary sulfurization life (x days at 115°F) is then determined as indicated above. The quantity of acid is decided upon by finding the set of curves (aluminium precipitation life and sulfurization life, such that the space between them at a distance of two days* from the sulfite axis corresponds to one-sixth of the developer capacity. The acid concentration represented by this chosen set of curves gives the acid concentration to use in the formula. With this fixing bath it is therefore possible to add a quantity of sulfite x (as represented by a developer life of 6x) in addition to that already present in the formula before a precipitate of aluminium sulfite is formed. The formula given above represents a suitable stable acid hardening fixing bath which might be used in cases where only a relatively small quantity of developer is carried into the fixing bath. Fig. 8 shows the effect of the addition of developer on the hardening properties of this formula. It is seen that the hardening at first is not as high as desired, but with the addition of further developer (about 5% MQ 25) the hardening falls off and the bath is rendered useless by the formation of a precipitate. (Continued on Page 40) EFFECT ~ DEVELOPED '-HARDENING PROPERTIES FIXING BATH 7. Effect nf age of fixing bath on its hardening properties. Fig. 8. Effect of the addition of developer on the hardening properties of a fixing bath