MANUFACTURE OF CASEIN. 29 
trouble need be experienced in handling that kind of material. The 
combination of acid in sour cream with the temperature required 
for pasteurizing has an injurious effect upon the normal handling 
of the resulting buttermilk. The degree of acidity which may be 
present in the cream at the time of pasteurization without seriously 
interfering with the normal working of the buttermilk curd for 
making casein has not been determined. As a large proportion of the 
casein of the best quality is used for coating paper, the numerous 
lots of casein made were tested with special reference to their adapt- 
ability and practical value for that industry. The tests applied in 
the paper industry, however, give results applicable in determining 
the value of casein for other purposes for which it may be used. The 
requirements of casein for high-class paper-coating work are rather 
severe, and lots not suitable for that work often can be used satisfac- 
torily for other purposes. 
The casein is used for the purpose of fixing the coating material 
to the paper in such manner as to make it a part of the paper. In 
case an insufficient quantity of casein is used the coating ingredients 
pull away from the paper when put to the test. By using more 
casein the coating material is held firmly to the paper, which serves 
as a practical means of determining the strength of the casein. The 
strength or adhesiveness of all the samples made was ascertained 
by a laboratory method used by the paper concerns, in which the 
quantity of casein required to hold the coating mixture properly is 
determined. 
In addition to the tests made in the laboratory large samples of 
buttermilk casein were sent to two paper manufacturers for the pur- 
pose of having commercial coating tests run on their large machines 
and in that manner determine its practical value and handling qual- 
ities. While the results obtained in the large coating machines did 
not always indicate the effect of the factor under observation in so 
marked a degree as was found in the laboratory method, they did 
demonstrate fully that a good grade of casein suitable for high-class 
coating and lithographing work can be made from buttermilk. 
The strength test was used almost entirely in these experiments 
as a basis for drawing conclusions as to comparative values of casein 
in stud} r ing the effect of the factor under consideration, as there was 
no trouble in obtaining a complete solution of the casein after adopt- 
ing a suitable method. The time required for the casein to dissolve 
is of importance, but slow dissolving does not necessarily indicate a 
poor grade, as the rate of dissolving may be influenced by factors 
that have no effect upon the strength. While the casein must dis- 
solve within a reasonable time, its practical value is determined in 
the final outcome largely by its strength or ability to hold the coat- 
ing material. 
