Xew York Agricultural Experiment Station. 319 



we have prepared and studied two sets of compounds of casein with 

 bases, in one of which 1 gram of casein combines approximately 

 with 1 . 125 X 10^ gram equivalents of base, while in the other 

 1 gram of casein combines with about 2.25 x 10* gram equivalents 

 of base. 



We will next take up the details of our experimental work in 

 preparing acid caseinates of the bases of the more common alkalis 

 and alkaline earths. 



The specific object of our work was to ascertain the smallest 

 quantity of base with which casein combines to form a definite salt. 

 In the volumetric work our method of procedure was as follows: 

 In 200 cc. of iT alkali, we dissolved 5 grams of pure casein as quickly 

 as possible and then made the volume to 250 cc. Each 50 cc. of 

 this solution therefore represents 1 gram of casein dissolved in 50 cc. 

 of ^ alkali. A preliminary or trial determination was next made in 

 the following manner: Into a 300 cc. Erlenmeyer flask, we measure 

 50 cc. of the caseinate solution and then add, a drop at a time, 

 some ^ HCl, until we have used 5 cc, the contents of the flask being 

 kept in constant agitation in order to prevent premature precipi- 

 tation of casein. After addition of the 5 cc. of acid, a portion of the 

 contents of the flask is centrifuged, in order to cause the sedimenta- 

 tion of precipitated casein, if any, a precipitate serving as an indi- 

 cator. A sedimentation tube of 50 cc. capacity can be used; the 

 precipitate collects in the lower V-shaped portion. It is possible in 

 this manner to detect the casein precipitated by 0.20 cc. of ^ HCl. 

 In case no casein is precipitated by the first addition of 5 cc. of acid, 

 another equal amount of acid is added and a portion of the mixture 

 centrifuged; the process of adding 5 cc. portions of acid and centri- 

 fuging is continued until a permanent precipitate of casein is 

 obtained. This shows, within 5 cc. of § HCl, how much acid is 

 required to start definite precipitation of the casein. In order to 

 ascertain the exact point more closely, another set of determinations 

 is made, using 50 cc. of the caseinate solution and adding in the 

 same cautious manner an amount of ^ HCl which is 5 cc. less than 

 the amount causing the first appearance of a permanent precipitate 

 in the trial or preliminary determination. The acid is now added 

 in small amounts with constant agitation of the mixture to prevent 

 the premature separation of any precipitate, and centrifuged after 

 the addition of each 0.25 cc. The point at which a permanent 

 precipitate first appears is noted; the addition of acid is continued 

 until all the casein is precipitated and this point is also noted. In 

 our work this method of determination was repeated several times 

 with each combination of casein and alkali and three different casein 

 preparations were used in preparing each caseinate. We will now 

 present the results of our experimental work in connection with the 

 unsaturated or acid caseinates of, first, ammonium, sodium and 

 potassium, and, second, barium, strontium and calcium. 



