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 maimer 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 by 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 w T eight 

 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 149° 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 grams of the solution will represent, one of casein. 

 Some samples of casein may require more than the specified quantity 

 of borax or other alkali. No trouble was experienced in dissolving 

 the samples reported in the proportion of borax given. 



One hundred grams 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 grains 

 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 

 grains 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 property 

 to the paper. Best results were obtained bj 7 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. 



