New YorkK AGRICULTURAL EXPERIMENT STATION. 343 
cows far along in lactation and high in casein (3.5 to 4 per 
ct.), we have had to use as high as 35 to 40 cc. of acid. We 
have seldom found any case in which 25 cc. of acid was exces- 
sive. The amount of acid may be 2 or 8 cc. in excess of. that 
required to effect complete precipitation without seriously 
affecting the accuracy of the results, provided the temperature 
of the mixture is below 75° I’. At temperatures above 75° F., 
good results are attainable, but care must be taken not to 
use much excess of acid; and, of course, the higher the tem- 
perature, the less will be the amount of acid required for 
precipitation. Extra care must be used at higher tempera- 
tures in regard to the use of any marked excess of acid for 
the following reason: The higher the temperature, the more 
easily does casein dissolve in the presence of free acid,’ the 
effect being to reduce the results of the test in percentage 
of casein. In working at temperatures under 65° F., the casein 
Separates more slowly or requires more acid to separate 
promptly. In case of milk that is much below 65° F., it is 
well to use for dilution water that is at a temperature of 
about 80° F. 
(4) Filtration of casein. After the casein is completely 
precipitated, pure, soft water (preferably, distilled), is added 
until the 200 ce. mark is reached and the contents are then 
‘vigorously agitated 10 or 15 seconds, in order to make the 
distribution of acid through the mixture as uniform as possi- 
ble. The contents of the flask are then poured on a dry filter 
and the filtrate caught in a beaker or cup. The funnels, filters 
and beakers or cups should all be dry before being used. It 
is well generally to allow the filtration to continue until prac- 
tically all of the liquid has run into the beaker or cup. 
(a) Rapidity of filtration— The usual time of filtration 
should not exceed 3 to 5 minutes. The rapidity depends upon 
the temperature of precipitation and the completeness of the 
separation of casein. In general, the higher the temperature 
of the mixture when precipitated with acid, the more rapid 

§N. Y. Agrl. Expt. Sta., Tech. Bul. No. 3. 
