20 
interval of time, this condition apparently resulting from a difference 
in oxidizing power in the first place, and also from a difference in 
the conduct of the blood toward phenolphthalein in alkali after this 
substance has been once formed. 
In the second place, as is well known, a large excess of alkali 
destroys the colored substance first formed by the action of ’alkali on 
phenolphthalein by the formation of a colorless salt. The rate of 
decomposition of the colored compound of phenolphthalein and alkali 
seems to depend entirely on the concentration of the alkali. With 
large amounts of alkali the colored compound is destroyed imme- 
diately; with greater dilution and smaller amounts of alkali the col- 
ored compound is decomposed more slowly and gradually. That it 
gradually disappears from such a solution, however, may be seen from 
the following observations. 
In order to determine the effect of increasing amounts of sodium 
hydroxide on the color of phenolphthalein. five solutions were pre- 
pared. each containing 0.318 milligram of phenolphthalein in 1 c. c. 
of absolute alcohol and 1. 2. 3, 1, and 5 c. c. X 10 sodium hydroxide, 
together with sufficient water to make the total volume up to 7 c. c. in 
each case. The color of these solutions was then compared with that 
of a phenolphthalein standard, containing 0.318 milligram in 1 c. c. 
absolute alcohol. 1 c. c. X 10 sodium hvdroxide. and 5 c. c. of water, 
the standard being set at 5 divisions on the colorimeter scale. 
The following readings were obtained for the several solutions 
immediately and after twenty-four hours, the comparison being made 
with freshly prepared standard in each case. 
READINGS ON COLORIMETER. 
Quantity 
of sodium 
hvdroxide 
' X/ 10 
Immedi- 
ately. 
After 24 
hours. 
Standard. 
c. c. 
- 
1 
4.9 
8.7 
5 
2 
4.95 
16.1 
5 
3 
5.4 
22. 75 
5 
4 
Lost. 
Lost. 
5 
5 
13.4 
22.6 
5 
Even at a dilution five times as great as that employed in the above 
series of experiments, viz. with X 50 sodium hydroxide, the color of 
phenolphthalein in alkali shows a tendency to fade on standing, but by 
no means so rapid and pronounced as with X 10 sodium hvdroxide. 
Five solutions were prepared, each containing 0.318 milligram phe- 
nolphthalein in 1 c. c. absolute alcohol, and 1. 2. 3. 1, and 5 c. c. X 50 
sodium hydroxide and sufficient water to make the total volume of the 
several solutions up to 7 c. c. in each case. These were compared with 
a fresh standard solution of phenolphthalein containing 0.318 milli- 
