New York AGRICULTURAL EXPERIMENT STATION. 283 
The curve actually obtained (Fig. 22) is concave and 
gradually approaches the horizontal position without the oc- 
currence of a break at any point. The curve reaches its minimum 
at a point near that neutral to phenolphthalein, but it does not 
appear that this point indicates the normal salt any more than the 
nunimum on the phosphoric acid curve indicates Na,PO,. It in- 
dicates rather the presence of sufficient excess of casein to depress 
the amount of hydrolytically freed NaOH to a negligible quantity. 
If we adopt Sjoqvist’s method, and extend the asymptote of the 
upper part of the curve, until it cuts the horizontal line tangent at 
the minimum (dashed lines Fig. 22), the intersection indicates an 
equivalent weight of casein less than one-third that estimated from 
the point neutral to phenolphthalein. The assumption of Laqueur 
and Sackur’s, that the latter indicates approximately the true equiva- 
lent weight of casein is not confirmed. It does not appear that this 
can be ascertained by titration with acid-alkali indicators any more 
than can that of phosphoric acid, altho as applied by Robertson! it 
may furnish the basis of a convenient empirical method for quantita- 
tive estimation of the proteid. 
EXPERIMENTAL. 
N 
We dissolved varying amounts of casein in 100 cc. of _** 
100 
NaOH and determined the point of minimum conductivity by the 
method of repeated approximation, finding the point within wide 
limits, then working within these and finding narrower limits, etc. 
The methods of manipulation in agitating casein with alkali and in 
measuring conductivities were the same as in the case of acids. The 
solutions were thus in contact with the electrodes only a short time, 
avoiding chances of the difficulty mentioned by Laqueur.? 
We obtained the following results graphically expressed in Fig. 
@egisinoein each. case 100.cc. of _N NaOH with the amounts of 
100 
casein indicated. 

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*Am. Jour: Biol. Chem., 2:317. 
* Beitr, Chem. Physiol. u. Pathol. 7:275. 1906, 
