New YorK AGRICULTURAL EXPERIMENT STATION. 345 
coloration that disappears within 5 seconds. In the case of 
milk rich in phosphates, the solution usually grows quite 
turbid as the neutral point is approached, making it neces- 
sary to use more care in observing the color of the end-point 
of the reaction. 
If one desires to make a second titration of the same filtrate, 
one can use 50 cc. of the remaining portion, multiplying the 
result by 2 and recording this as B. 
(6) Calculation of results. The calculation of the percent- 
age of casein from (1) the amount of acid used (A) in pre- 
cipitating the casein and (2) the amount of alkali used (B) 
in neutralizing 100 cc. of filtrate, is very simple. Divide A 
by 2 and from the result subtract B; or, expressed as a 
formula, 
A _ B= Per ct. of casein in milk. 
Kixample: One uses 30 ce. (A) of acid in precipitating casein 
and 11.95 ce. (B) of alkali in neutralizing 100 ce. of filtrate 
(one-half of filtrate from the casein precipitate, corresponding 
to 9 grams of milk). Substituting 30 for A and 11.95 for B 
in the formula we have 
* — 11.95 = 15 — 11.95 = 3.05 (the percentage of casein in 
milk). 
(7) Use of preservatives. In making a casein determination 
by this mehod, it is desirable when possible to use milk not 
more than 24 hours old, which has been kept in a cool place. 
Milk which is sour or which coagulates on heating can not be 
used with satisfactory results. However, by adding to fresh 
milk powdered mercuric chlorid (corrosive sublimate) in the 
approximate proportion of 1 part to 1,000 or 1,500 parts of- 
milk, and then keeping the mixture at a temperature of 50° F. 
or lower, we have been able to obtain satisfactory results with 
milk that had been kept two to three weeks. Milk thus treated 
should be shaken often enough to keep the fat well incorpor- 
ated in the body of the milk. The desired amount of mercuric 
