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Fine-Grain Developers — Carlton and Crahirce 42')
6; Effect of Addition of Hypo. Comparison of developers Nos. 19 and 26 (Table II) shows the effect of the addition of a small concentration of hypo to a modified borax developer. The addition of hypo decreases the rate of development and the speed of the emulsion. The effect of hypo on graininess will be discussed later.
7. Practical Methods of Changing the Rate of Dea^elopMENT. The date of development can be increased by increasing the concentration of boiax as shown in Fig. 4 and to a lesser degree by increasing the concentration of the developing agents if extra borax is added to compensate for their acidity.
The rate of development can be decreased by decreasing the quantity of developing agent, by decreasing the quantity of borax, by adding sodium sulfate, or by any combination of these three methods.
By using the boric acid-borax combination the rate of development can be controlled to produce any desired rate of development within the immediate range of that produced with the standard borax developer.
III. Effect of Age on the Borax DE^^ELOPER
A, Without Use For commercial purposes the borax developer keeps satisfactorily when mixed in large quantities and used soon after it is prepared. It was found, however, that several samples of developers gave an increased rate of development wdien they w^ere tested after having been stored for several w^eks. This w^as caused by an increase in the alkalinity of the developer. Analytical tests showed that there w^as no change in the concentration of the sodium sulfite and further tests are in progress to determine the cause for the change in alkalinity.
For sensitometric purposes, however, a developer is needed whose rate of development does not change with keeping.
A comparative keeping test was made w^ith the regular borax developer and a buffered borax developer with the following composition :
Elon ■ 2.0 grams
Hydroqiiinone 5.0 grams
Sodium sulfite (desiccated) 100 grams
Borax 8.0 grams
Boric acid 8.0 grams
Water to 1 liter