222 REPORT OF THE CHEMIST OF THE 
THE SOLUBILITY OF CASEIN IN DILUTE ACIDS. 
The ready solubility of casein in acids of N-10 or N-2o0 con- 
centration, especially hydrochloric acid, has been a familiar fact for 
a long time, but little has been done in studying the solubility of 
casein in acids much above N-1oo dilution. Our work shows that 
casein is appreciably dissolved at 25° C. by hydrochloric and lactic 
acids of N-1000 dilution, and by N-125 acetic acid. In all cases the 
solubility is markedly increased by increase of temperature. 
Evidence of solution can be furnished by the following observa- 
tions : 
(1) Viscosity of solution. After being treated with casein by 
the method described on p. 210, acids show marked viscosity. In 
the case of slight solution of casein, this is shown by the readiness 
with which foam is produced when the flask containing the filtrate 
is shaken, and also by the length of time the foam persists. The 
behavior of the foam is very different in amount and duration from 
that formed by agitating a solution of acid that contains no dis- 
solved proteid. In the case of more marked solution, viscosity is 
more readily noticed, and the liquid foams noticeably while being 
drawn through the filter; it also filters more slowly. In cases of 
very marked solution, filtration, even by suction through a thin 
asbestos mat, was difficult and the filtrate consisted largely of foam. 
(2) Behavior of solution on adding alkaliim The clear filtrate 
~on titration with N-100 NaOH becomes opalescent and varies from 
that to milky turbidity and even to the formation of a heavy curd- 
like precipitate, according to the amount of casein in solution. 
These phenomena appear before neutrality is reached and disappear 
before sufficient alkali is added to give a permanent color with 
phenolphthalein. In the case of precipitation, the readiness with 
which the precipitate dissolves varies with the rate at which the 
alkali is added. When the alkali is added slowly, the precipitate 
forms large flakes and these, once formed, redissolve quite slowly. 
On the other hand, if alkali is rapidly added in amount sufficient to 
redissolve any precipitate, the particles of casein, not having time 
to form large aggregations, redissolve almost instantly, so that only 
a transient, opaque milkiness is observed before redissolving takes 
place. 
Bisiin ee 
