234 REPORT OF THE CHEMIST OF THE 
The solution of casein in dilute acids may be the result of the 
formation of a soluble casein-acid salt, similar to an amido salt, or 
it may be the result of the decomposition of the casein molecule, 
part of which is split off and gives the reaction for proteid in solu- 
tion. In the latter case, we should expect some change in the prop- 
erties of the undissolved portion, and this is found to be true. An 
attempt was made to determine the percentage of casein dissolved 
at 25° C. by N-125 HCl in 3 hours; the undissolved casein was 
collected in a Gooch crucible, washed, and dried at 100° C. At the 
time of filtration the undissolved residue presented a swollen, gela- 
tinous appearance and, when placed in the steam oven to dry, it 
melted completely, running through the perforated bottom of the 
crucible. The dried mass looked like dried albumin. The experi- 
ment was repeated with the same result. Casein itself can be heated 
to 120° C. or higher without visible change, and casein that has 
taken up acid without any solution of the proteid does not appear 
either to swell or gelatinize, and it can be dried in a steam oven 
without difficulty. When a part of the casein goes into solution, 
the undissolved residue appears to undergo some profound change 
in its properties, and this fact suggests the possibility of molecular 
decomposition. The scope of our work did not permit us for the 
time being to carry further our study into details of this interesting 
change. 
THE ACTION OF HYDROCHLORIC ACID UPON CASEIN WITHOUT 
SOLUTION. 
In the foregoing pages we have studied the conditions under 
which casein goes into partial solution when treated with dilute 
acids, and also those under which such solution may be avoided. 
Working under the latter conditions as completely as possible, we 
now purpose to ascerta.n to what extent and under what conditions 
casein takes up acid from dilute solutions when no casein dissolves. 
It has already been shown by both titration and conductivity 
methods (Fig. 6, p. 227, curve for o° C.) that when a gram of 
casein is shaken with 100 cc. of N-125 HCl at 0° C., about one-half 
