344 REPORT OF THE CHEMIST OF THE 
should be the filtration, other conditions being uniform, In 
case of insufficient acid, the filtration is slower. 
(b) Appearance of filtrate—The filtrate should be quite 
clear, though this is not always a sure indication that the 
right amount of acid has been added to effect complete precipi- 
tation and release casein entirely from its combination. Some- 
times the filtrate may be clear when not quite enough acid 
has been added, in which case the percentage of casein found 
is apt to be low; under such circumstances, filtration is usually 
slow. In case of milks rich in fat, a slight turbidity may 
appear, due to fat-globules in the filtrate. The filtrate should 
be free from all signs of marked turbidity or anything like 
milkiness. If such a filtrate appears, a new sample of milk 
should be taken and the operation repeated from the begin- 
ning, more acid being used than before. With a little experi- 
ence, especially under proper instruction, no difficulty should 
be found in recognizing quickly when the casein is separated 
so as to give satisfactory results. 
(5) Titration with alkali. After filtration is completed, one 
measures 100 cc. of the filtrate with the pipette into a beaker 
or cup and then from the burette runs into this the standard 
alkali until a faint, but distinct, pink color remains clearly 
marked through the solution for half a minute or longer before 
beginning to fade. The number of cubic centimeters of alkali 
used is noted and this result is recorded as B. 
The last portions of alkali must be added carefully, a drop 
at a time, agitating the mixture well after each addition. The 
exact neutral point is not perfectly sharp on account of the 
presence of phosphates, and the appearance of the desired 
coloration is, therefore, not as sudden and pronounced as 
might be desired. With experience one should have no diffi- 
culty in getting within one drop of the correct amount of 
alkali. The chief precaution to be observed. is to have the 
same shade and duration of color every time. Thus one should 
not in one titration add alkali until a deep pink coloration 
appears, lasting for some minutes, and then in another, a 
