13 
That the amount of phenolphthalein formed as the result of the 
oxidation of phenophthalin can be accurately determined by this color- 
metric method, provided an excess of alkali, not too great, is present 
in the solution, may be seen from the following observation: 
A solution of phenolphthalein was prepared containing 0.159 grams 
of the substance in 100 c. c. of absolute alcohol. One cubic centi- 
meter of this solution, which we will call solution A, was mixed with 
5 c. c. of water and 1 c. c. N 10 sodium hydroxide. The color of this 
solution was then compared in the colorimeter with that of a standard 
solution of phenolphthalein containing 0.0318 grams of the compound 
in 100 c. c. of absolute alcohol, using the same quantity of water and 
sodium hydroxide. These solutions gave the following readings on 
the colorimeter: 
Solution A. 
Standard. 
1.1 
5 
1 
5 
The theory for these solutions is 1:5, inasmuch as the stronger 
solution contains live times as much phenolphthalein as the standard. 
On account of the very slight solubility of phenolphthalein in water, 
considerable difficulty has been encountered in the preparation of the 
standard solution of phenolphthalein with which to make the color 
comparisons. Hence it is, that during the progress of the investiga- 
tion, several such standard solutions of phenolphthalein have been 
employed, so that, in the majority of cases, at least, the results 
obtained in the several series of experiments are not strictly compara- 
ble, one series with another, but only the results of any particular 
series. among themselves. 
Another reason why the results of any particular series of experi- 
ments are only comparable among' themselves and not with those of 
any other series is that the oxidation of phenolphthalin by hydrogen 
peroxide under the accelerating action of blood is like the greater 
number of chemical processes influenced by- temperature; the rate of 
oxidation increasing, within certain limits at least, with rise of tem- 
perature, this effect being most noticeable for short intervals of time. 
That such is the case may T be seen from the following observations: 
Solutions were prepared containing 2 c. c. of the dilute solution of 
Amoss’ blood (normal), containing 1 cu. mm. of blood in 250 c. c. 
and 5 c. c. of the reagent. Glass-stoppered bottles containing these 
solutions were kept at 2° C., lfl° C., and 39° C., for fifteen minutes 
and one hour, respectively, at the end of which time the color of the 
several solutions was compared with that of a standard solution of 
phenolphthalein in N 10 sodium hydroxide. The standard was arbi- 
trarily set at 5 divisions on the scale of the colorimeter. The follow- 
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