A NEW HYDROGEN ELECTRODE FOR THE ELECTRO- 
METRIC TITRATION OF THE ALKALINE RESERVE 
OF BLOOD PLASMA AND OTHER 
FROTHING FLUIDS. 
By J. F. McCLENDON. 
(From the Physiological Laboratory of the University of Minnesota Medical 
School, Minneapolis.) 
(Received for publication, October 12, 1917.) : 
Van Slyke and Cullen have devised a practical method for the 
determination of the bicarbonate reserve of plasma, based on 
Van Slyke’s method for determining total CO. The method 
presented in this paper also determines the bicarbonate, but by 
titration of the alkali instead cf by the determination of the CO, 
of the NaHCO; molecule. 
At present the most accurate method of titrating the blood 
alkali against acid to a definite end-point is afforded by the gas 
chain, since the end-points of indicators are rendered indefinite 
by the proteins present. With the electrometric technique one 
may choose between two modes of titration, (1) adding a definite 
amount of acid and measuring the change in pH, or (2) as in ordi- 
nary alkalimetry, adding as much acid from a burette as is neces- 
sary to obtain a definite pH. Cullen (1917) in a recent paper 
has used the former method. The latter, however, has the ad- 
vantage that it permits one to choose an end-point so near the 
pH of circulating blood that comparatively little of the acid added 
combines with proteins and phosphates, so that only the bicar- 
bonate is titrated. 
In this paper apparatus is described for a convenient electro- 
metric titration by addition of acid until a desired end-point is 
reached. As end-point we have chosen the pH of water, which is 
7.00 at 23°. During the titration the free carbonic acid is reduced 
to approximately zero by washing out with hydrogen gas. Under 
- these conditions (pH = 7.0, H2CO3 concentration = 0) all the 
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