25 
pointed out certain advantages which phenolphthalin possesses over 
guaiaciim (van Deen’s test) and aloin (Rossel’s test). In 1906, 
Kastle and Amoss (80) employed an alkaline solution of phenol- 
phthalin in measuring the oxidizing power of the blood in health 
and disease. They showed that both the oxidizing power of the 
blood and its peroxidase activity,^ viz. its power to induce the oxi- 
dation of phenolphthalin by hvdrogen peroxide in alkaline solution, 
were directly proportional to its hemoglobin content. In 1908, 
DeMarde and A. Benoit (16) have also recommended an alkaline 
solution of phenolphthalin in conjunction with hydrogen peroxide 
as a reagent for blood, and have found it to be more sensitive than 
guaiacum or aloin. Still more recently, Pozzi-Escot (128) has made 
a few observations on the use of phenolphthalin as a reagent for 
blood. Pie criticises the work of Delearde and A. Benoit (16) se- 
verehy and seems inclined to attach no particular value to the 
reagent as a test for blood for the reason that other substances, such 
as extract of malt, saliva, pus, etc., and a great num_ber of the salts 
of the heavy metals, such as those of cobalt, manganese, iron, and 
lead, can accomplish the oxidation of phenolphthalin in the presence 
of hydrogen peroxide. 
In attempting to repeat some of our earlier observations, consid- 
erable difficulty was experienced in the preparation of the peroxidase 
reagent, viz, an alkaline solution of phenolphthalin containing hydro- 
gen peroxide. Similar difficulties have been experienced by other 
observers. (See Czyhlarz and von Fiirth, 43.) It was therefore 
deemed expedient to make further studies along this line with the 
view of determining more exactly the most suitable means of pre- 
paring the reagent, and also with the view of determining more care- 
fully than had hitherto been done the delicac}^ of the reagent and 
its applicability as a test for blood. 
PREPARATIOX AND STABILITY OF THE REAGENTS. 
In order to prepare phenolphthalin, phenolphthalein is dissolved 
in a considerable excess of 30 per cent sodium hjffiroxide solution 
and boiled with an excess of zinc dust until a few drops of the 
strongffi alkaline liquid no longer give the color of phenolphthalein 
after neutralization with hydrochloric acid and the addition of 
sufficient alkali to give a slightly alkaline reaction. The solution 
is then decanted from the excess of zinc dust and the phenolphthalin 
precipitated by acidifying with hydrochloric acid. The substance 
is then collected on a filter and purified by several crystallizations 
from water and alcohol in the following manner: The phenolphthalin 
is dissolved in the smallest quantity of boiling alcohol in which it 
will dissolve, filtered if necessary, and cold water gradually added 
with constant stirring until the compound is precipitated out as a 
178— Bull. 51—09 4 
