9 
labeled B. One set of the solutions A and B was then allowed to 
stand for fifteen minutes at room temperature, 30° C.. at the end of 
which interval 1 c. c. of A' 10 sodium hydroxide was added to A and 
1 c. c. of water was added to B. The depth of color of each was then 
determined by comparison with standard phenolphthalein placed at 
five divisions on the colorimeter scale, immediately and fifteen min- 
utes after the final addition of sodium hydroxide and water with the 
following results: 
15-minute series. 
READINGS ON COLORIMETER. 
Time. A. B. 
Immediately a 175. 5 
15 minutes 10. S 64. 6 
alt should be borne in mind that a large number on the scale of the colorimeter ^Duboscq-Pellin) 
signifies a faint coloration and the presence of a small amount of the colored substance, whereas, 
conversely, a small number on the colorimeter scale indicates a greater depth of color and a corre- 
spondingly larger amount of colored substance. For further details regarding this method of mak- 
ing the color comparison^ see footnote £>, p. 15, of this communication. 
f>B of course had stood altogether 30 minutes in contact with 1 c. c. N, 10 sodium hydroxide, at a 
total dilution of S to 9 c. c. 
A second pair of solutions A and B was allowed to stand in glass- 
stoppered bottles at 30“ C. for two hours, at the end of this time 1 c. c. 
of X 10 sodium hydroxide was added to A and 1 c. c. of water to B. 
The depth of color of each was then determined by comparison with a 
standard solution of phenolphthalein solution in alkali in the colorime- 
ter, the standard tube of the colorimeter being placed at 5 divisions 
on the scale, immediately and after standing fifteen minutes, with the 
following results: 
Two-hour series. 
READINGS ON COLORIMETER. 
Time. 
Immediately 
15 minutes . . 
A. 
B. 
17S 
6.7 
3.9 
6. 7 
The third set of solutions was allowed to stand for three hours at 
ordinary temperature, at the end of which time 1 c. c. of X 10 sodium 
hydroxide was added to A and 1 c. c. of water to B. The color intensity 
of both solutions was then determined immediately in the manner 
already described with the following results: 
Three-liour series. 
READINGS ON COLORIMETER. 
Time. A. B. 
_ 
Immediately ‘235 7.6 
15 minutes 65 7. 5 
