318 Report of the Department of Chemistry of the 



solution is neutral to phenolphthalei'n. Expressed in another form, 

 1 gram of casein combines with 9 x 10"'* gram equivalents of calcium. 

 This compound is commonly known as basic calcium caseinate. 



preparation and composition of unsaturated or acid 



caseinates. 



Compounds of casein with bases, in which less base is present than 

 in the basic calcium caseinate described above, have been reported. 

 Soldner^ obtained a compound of casein and calcium containing 

 1.11 per ct. Ca (equal to 1.55 per ct. CaO); or, expressed in another 

 form, 1 gram of casein combines with 5.55 x 10"^ gram equivalents 

 of calcium. This compound is neutral to litmus but acid to 

 phenolphthalein, and has been commonly known as neutral calcium 

 caseinate. This compound as prepared by Van Slyke and Hart- 

 contains about 1.07 per ct. Ca (equal to about 1.50 per ct. CaO), 

 or 1 gram of casein combines with 5.35 x 10"* gram equivalents of 

 calcium. Courant^ believes that, in addition to the basic and neutral 

 compounds of casein and calcium, a third exists, in which the calcium 

 is present in about one-half the amount contained in the neutral 

 compound and one-third that contained in the basic compound; he 

 regards them as mono-, di- and tri-calcium caseinates. Timpe* 

 reports a compound containing 0.961 per ct. Na (equal to 0.868 

 per ct. CaO or 0.62 per ct. Ca; or 1 gram of casein combines with 

 3.1 X 10'^ gram equivalents of calcium). Long^ was able to dissolve 

 1 gram of casein in just one-half the amount of alkah required for 

 the phenolphthalein neutralization, and therefore inferred the 

 existence of acid caseinates containing one-half the amount of base 

 contained in basic calcium caseinate. The existence of such a 

 combination is questioned by Robertson.'' 



In the course of our work, we became convinced that casein forms 

 compounds containing less base than any of those reported by other 

 workers. While we were at work on this point, an article by Robert- 

 son^ appeared, in which was reported a combination of casein and 

 sodium hydroxide, 1 cc. of the alkali combining with 0.877 gram 

 of casein. Our further work confirms Robertson's results, although 

 we have used a different method of procedure. In addition, we 

 have been able to prepare and isolate several salts for analj^sis. Our 

 study of these individual salts shows that ammonium, sodium and 

 potassium compounds possess properties of solubility very different 

 from those of barium, calcium and strontium. As previously stated, 



^Landw. Fersztc/is.-<S<a<., 35: 351, 1888. 



2N. Y. Agrl. Expt. Sta. Bull No. 261, 1905. 



'Pfiiiger's Archiv. Physiol, 50: 109, 1891. 



^Arch. Hyg. 18: 1, 1893. 



^Jour. Am. Chem. Soc, 28: 372, 1906. 



f'Jour. Biol. Chem., 2: 336, 1906. 



^Jour. Physical Chem., 13: 469, 1909. 



