New York AGRICULTURAL EXPERIMENT STATION. 239 
the final amount of acid taken up by 1 gram of casein varies from 
the equivalent of 35.36 to 480.3 cc. N-1000 HCl, which amounts 
were taken up by casein in contact with solutions of acid whose 
final concentrations were 0.2400 and 3.192 respectively. 
(3) If we divide the amount of acid contained in 1 gram of 
casein by the amount of acid contained in 1 cc. of the surrounding 
solution at equilibrium, we obtain a ratio, about 147, which is 
approximately constant, as shown in the sixth column. The lower 
value, 142.8, obtained with N-1000 acid is probably due to incom- 
plete attainment of equilibrium. The slightly higher result in the 
case of N-125 acid is to be expected, since appreciable solution of 
proteid occurs. 
(4) The acid, however small the amount used, was in no case 
completely taken up by casein, but the ratio of acid in casein 
to acid in surrounding solution approaches an equilibrium constant, 
about 147. 
The results given in the fourth column of Table VIII are 
expressed in F ig. 7 in the form of curves, which illustrate the fact 
that the process by which casein takes up acid does not follow the 
law of definite combining proportions, and that the amount of acid 
fixed by a gram of casein in the presence of an excess of acid is 
not constant, but increases with increasing concentration of acid. 
Amount of acid taken up by casein dependent upon the concen- 
tration of acid present—RIn order to illustrate more fully the fact 
that the amount of acid taken up by I gram of casein is dependent, 
not upon the absolute amount of acid present, but upon the con- 
centration, we give the data embodied in Table IX. The three 
series of experiments were carried on at different times and for 
different purposes, which accounts for the lack of uniformity in the 
time intervals used. It will be noticed that, while the initial con- 
centration of the acid in the third series is twice that of the others, 
the final concentrations are fairly comparable in all three cases, which 
is due to the larger relative proportion of casein used in the third 
series. The mixtures were shaken constantly for the periods indi- 
cated and kept at 25° C, 
