214 Report OF THE CHEMIST OF THE 
INTRODUCING CASEIN INTO ACID SOLUTION. 
The desired amount of acid is first delivered into the reaction 
flask and then to this is added the weighed amount of casein. In 
the experiments carried on at 45° and 0° C., the acid solution in 
the flask was allowed to come to the desired temperature before 
the casein was introduced. 
METHODS OF AGITATING THE MIXTURE OF CASEIN AND ACID. 
In most of the experiments made at room temperature, we placed 
the flasks in a revolving apparatus, which kept the casein in con- 
stant motion throughout the acid solution. In the experiments 
made at 0° and 45° C., the agitation was performed by occasional 
shaking by hand. When the mixtures of casein and acid were 
shaken only at intervals, the reaction rate was somewhat slower 
and less regular than when agitation was continuous, the irregular- 
ity being shown by points lying noticeably off their curves occa- 
sionally, but the difference was not great and, of course, the equi- 
librium finally reached was not altered. 
METHOD OF FILTRATION. 
When the casein has been in contact with the acid as long as 
desired, the liquid is filtered into a 200 cc. Jena flask through a 
platinum Gooch crucible. The receiving flasks are cleaned and 
dried in the manner already described above. The Gooch crucibles, 
before use, are rinsed with conductivity water, then a thin mat of 
asbestos, previously suspended in conductivity water, is formed in 
the bottom of each. Before use the whole is dried in order to pre- 
vent any dilution of the filtrate by adherent water. To insure the fil- 
trate further against possible contamination, the precaution is taken 
to rinse the receiving flask with two portions, of a few cubic centi- 
meters each, of the filtrate first drawn through, these rinsings being 
thrown away. In this way, one can filter 100 cc. of liquid in less 
than a minute, thus reducing to a minimum the exposure of the 
solution to air. Water having a conductivity of 31.5 X 10-® in- 
creased only 0.2 to 0.3 X 10-° after being passed through such a 
filter in a blank experiment. 
