
New York AGRICULTURAL EXPERIMENT STATION. 48% 
XVIII. THE DETERMINATION OF CASEIN IN COWS’ 
MILK (TECHNICAL). 
The methods originally proposed by Hoppe-Seyler and Ritt- 
hausen have been commonly employed for the separation and 
determination of casein in cows’ milk. In both methods, the 
milk is diluted with water and a small amount of acetic acid is 
added. The precipitation is rendered complete, in one case, by 
raising the temperature to 40° C., and, in the other case, by pass- 
ing a current of carbon dioxide through the mixture at ordinary 
temperatures. The precipitate is filtered, washed first with 
water, and then with ether to remove fat and is finally dried and 
weighed on the filter. The absence of specific directions touch- 
ing several steps of the operation led me to investigate some of 
the conditions pertaining to the determination of casein, among 
which were the following: 
1. Comparison of the two methods. 
2. Influence of amount of acid used in precipitating casein. 
3. Use of different acids in precipitating casein- 
4, Influence of temperature and time of digestion on precipita- 
tion of casein. 
5. The precipitation of casein in fresh and in old milk. 
6. The use of preservatives in keeping. milk, and influence on 
the determination of casein. 
The tedious method involved in washing the precipitated casein 
free from fat by ether and in subsequent drying and weighing on 
the filter paper was entirely discarded. The precipitated casein 
was washed by decantation and on the filter two or three times. 
The filter and contents were then treated by the ordinary 
Kjeldahl method for the determination of nitrogen, the factor 
6.25 being used to convert the amount of nitrogen into an equiv- 
alent of casein, when this was desired. This use of the Kjeldahl 
method in determining the amount of casein was suggested and 
employed sometime since by several chemists and is now very 
generally used in the analysis of dairy-products. The advan- 
tages of its use over the old method in point of accuracy and 
simplicity are too evident and too well known to deserve further 
mention. 
(1). Comparison of results obtained by precipitating casein in 
milk at a temperature of 40° C. without carbon dioxide and with 
