New York AGRICULTURAL EXPERIMENT STATION. 229 
4 cc. N-1o acid, an amount about eight times that found by Van 
Slyke and Hart (Bulletin No. 261, p. 21). 
(2) The formation of a soluble substance from casein by the 
action of acid is effected when there is an increase in temperature 
or in the time of contact between the acid and casein. For conven- 
ience, we may term this soluble substance soluble acid-casein, without 
considering the question as to whether it is a salt of casein or a 
proteolytic product. 
(3) More casein goes into solution in 5 minutes at 45° C. than 
Hes uours at of C. - 
(4) The soluble substance appears to be a compound of casein 
and acid. This is indicated by the fact that there is a decrease in 
the conductivity of the acid simultaneous with the formation of 
the soluble acid-casein. The decrease is so marked that there is 
no doubt that the formation of the soluble compound is accompanied 
by fixation of hydrochloric acid. Doubtless the soluble acid-casein 
has appreciable conductivity of its own, as already mentioned in 
the case of other proteids, so that even the conductivity results for 
the amount of acid fixed are somewhat too low. 
(5) The method of determining by titration with alkali the 
amount of acid remaining unaffected by treatment with casein is 
thoroughly unreliable in the presence of soluble acid-casein. 
In connection with the data here presented, it would seem that 
the results of the experiments above described ought to emphasize 
the fact that caution should be used in the determination of free 
acid by titration in liquids, such, for example, as gastric juice, 
which have been in contact with proteids. Simon? gives titration 
with sodium hydroxide, using phenolphthalein for indicator, as the 
method for estimating the acidity of the gastric contents; and he 
also states that the acidity is increased by the ingestion of albumin- 
ous food. This would naturally be found so by the titration method, 
because the proteid in solution would neutralize part of the alkali 
used in titration and thus increase the amount required. 
Effect of temperature and concentration upon the rate at which 
acids dissolve casein.— We present below in Tables V, VI and VII 
results indicating the effect of temperature and concentration of 

* Physiological Chemistry, p. 128. 1904. 
