178 
a clear and fast filtering separation, but if the milk is low in casein a little less 
acetic acid should be used. The separated precipitate is now filtered through 
a filter (9-11 cm. filter), the flask rinsed out thoroughly and poured on the 
filter, preferably cold. If a strong stream of water is directed against the 
filter, the casein washing is facilitated. About 250 to 300 cc. of water should 
pass through the filter to insure the removal of all traces of acetic acid. The 
precipitate, together with the filter paper, is now returned to the Erlenmeyer 
flask in which the precipitation was made. To this is now added 75 ce. of 
distilled water, free from carbon dioxide, and then a few drops of phenol- 
pthalein and 10 ce. of zs 
‘ potassium hydroxide. A rubber stopper is placed 
in the flask and the contents shaken vigorously. Complete solution is easily 
indicated by the disappearance of the white casein particles. After solution 
the stopper is rinsed off into the flask with carbon dioxide free water and 
Ni 
1¢ 
It is necessary that a blank be run parallel with the determination. For 
immediately titrated with acid to the disappearance of the red color. 
example, suppose it required 7.20 ce. of acid to make the pink color just 
disappear and the blank amounted to .2 c¢., the percent of casein would be 
10 — 7.4 = 2.60 per cent. casein. Precatuions necessary. First, water free 
from carbon dioxide, must be used. Second, the titration should be made 
as soon as solution of casein has taken place. This will be from half an hour 
N 
to an hour after adding the alkali. Repeated shaking hastens solution. 
Results obtained by Hart as compared with the official method. 
PERCENT CASEIN. 
Volumetric Method 
Official Method. (Hart). 
sere = a) 
ahha be 3.05 
2.87 2.85 
1.90 1.85 
2.30 2.25 
PAR iff 2.30 
The next volumetric method to be considered is the Formol titration 
method. This is perhaps the most rapid method of the three volumetric 
methods, for estimating the proteids in milk. It was pointed out in 1900 
by Hugo Schiff that when formaldehyde was added to amino acids, the acid 
