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272
REES AND ANDERSON
September
calibration grid as is shown in Fig. 2 or by calculation using equations such as (2) and (3).
DETERMINATION OF ABSORBANCY INDICES
Prepare mixes containing all the mix ingredients with the exception of hydroquinone, using concentrations of Elon covering the expected range. Dilute 1 milliliter of each of the mixes with 100 milliliters of pH. 5 acetate buffer and determine the absorbancies at 270 and 290 millimicrons.
In the same manner, prepare mixes containing hydroquinone but no Elon and determine their absorbancies at 270 and 290 millimicrons after dilution with pH. 5 acetate buffer.
Prepare a basic mix. Dilute with the acetate buffer and determine the absorbancies at 270 and 290 millimicrons. Subtract
the absorbancies of the basic mix from the absorbancies of each of the standard mixes containing Elon or hydroquinone and determine the "absorbancy indices"11 according to the equation
Aa a*=bC>
(1)
where
0.22 0.24 0.26 0.28 0.30 0.32 0.34 036 0.38
Absorbancy at 270 mM
Fig. 2 — Typical calibration grid.
as4 = absorbancy indices
A» = absorbancy of sample
b = length of solution path
C = concentration* of Elon or hydroquinone.
* The absorbancy indices in tihis paper have, for convenience, been calculated expressing the concentrations a|s the concentrations of Elon and hydroquinone in the original developer solution. Since the cells used throughout this work had solution paths of 1.000 =±= 0.005 centimeter, the length (b) in (1) has been assumed as unity and constant.