30 BULLETIN 661, U. S. DEPARTMENT OF AGRICULTURE. 
While the test used in determining the strength of the casein can 
not be regarded as highly accurate from a scientific standpoint, it is 
more or less valuable in determining in a practical manner the rela- 
tive value of different samples of casein. The general handling 
quality of the different lots of casein was observed during the process 
of dissolving and also during the actual coating work. Difficulties 
encountered with the solubility or working properties of the samples, 
caused b}^ any factor introduced to study its effect upon the quality, 
will be discussed later under the heading of the particular factor. 
ADHESIVE OR STRENGTH TEST. 
Fifty grams of casein ground fine enough to pass through a screen 
with 20 meshes to the inch is weighed into a casserole whose weight 
is known, 100 cubic centimeters of cold distilled water is added, the two 
mixed well and allowed to stand for a short time, when 90 cubic centi- 
meters more of distilled water is added in which 5 grams of borax 
has been dissolved. Distilled water is then added until the mixture 
weighs 250 grams, and the casserole placed in a water bath having 
a temperature not to exceed 119° F. (65° ^C.) and stirred until the 
casein is dissolved. When the casein is completely dissolved more 
water must be added to take the place of that lost by evaporation, 
so that each 5 grains of the solution will represent one of casein. 
Some samples of casein may require more than the specified quantity 
of borax or other alkali. Xo trouble was experienced in dissolving 
the samples reported in the proportion of borax given. 
One hundred grains of china clay or kaolin, previously dried at the 
temperature of boiling water for one hour, is weighed into a heavy 
casserole, and 70 cubic centimeters of distilled water added and mixed 
to a smooth paste, care being taken to work up any lumps that may 
settle to the bottom. After weighing the casserole with its contents 
of clay paste. 30 grams of the casein solution, representing 6 grams 
of casein, is added to it and thoroughly mixed with the paste. A 
stiff brush is helpful in getting a good mixture. A thin coating of 
the mixture is then applied to several small sheets of test paper by 
means of a thin brass scraper or camel's-hair brush, using care to 
spread uniformly. The casserole is again balanced and 5 additional 
grams of the casein solution added, the solution well mixed and an- 
other set of test sheets coated, continuing the procedure of adding 
5 grams of the casein solution and making a set of test sheets until 
sufficient casein has been added to hold the coating mixture properly 
to the paper. Best results were obtained by using the brass scraper, 
which requires that the paper be placed on a perfectly flat surface, 
such as a piece of smooth plate glass. When using a brush the coating 
mixture should be painted on very quickly, first lengthwise and then 
crosswise. 
