400 CHEMISTRY OF THE PROTEIDS CHAP. 



Caseinogen is precipitated from a solution of its salts, and also 

 from milk by small quantities of mineral acids and by larger amounts 

 of acetic acid, but it dissolves on adding an excess of acid. Caseino- 

 gen is most readily prepared by Hoppe-Seyler's method as modified 

 by Hammarsten. 1 



Precipitate milk with acetic acid, dissolve the precipitate in dilute 

 ammonia or in sodium carbonate, taking care to avoid the solution 

 becoming alkaline, and repeat the process several times. Free the 

 caseinogen thoroughly of fat by means of alcohol and ether, and then 

 treat it again with acetic acid and soda-solution. There is no danger 

 of denaturalisation if any marked alkaline reaction be avoided. The 

 de-fatting is rendered very much more easy if, instead of the pure 

 milk, we employ centrifugalised milk from which the cream has been 

 removed. 



Caseinogen and its salts are salted out by sodium chloride, 2 

 magnesium sulphate, 3 and sodium sidphate 4 in saturated solutions. 

 The limits for ammonium sulphate 5 are for the main bulk of the 

 caseinogen between 2*2 and 3*6, but a slight turbidity manifests 

 itself already at 1'2. 



The other precipitation-reactions are the same as in the case of 

 ordinary albumins, but Schlossmann G has found potash-alum in suit- 

 able concentrations to precipitate the caseinogen of milk without also 

 precipitating the other albumins ; excess of potash-alum redissolves 

 the precipitate, however. 



A true heat-coagulation is not shown by caseinogen, for the 

 solutions of its salts may be boiled without undergoing a change. In 

 a dry state, however, caseinogen, according to Laqueur and Sackur, 7 

 becomes partly insoluble on being heated from 94 to 100, while 

 according to the older statements of Hammarsten, 8 it requires a 

 temperature of from 120 to 130. Halliburton 9 noticed a change at 

 75 = on heating caseinogen suspended in water. 



What really happens to the caseinogen when milk is boiled is 

 not yet known ; 10 pure calcium-caseinogenate undergoes hydrolysis, 



1 0. Hammarsten, auto-abstract in Maly's Jahresber. f. Tierchemie, 4. 135 (1874) ; 

 Zeitschr. /. physiol. C/iem. 7. 227 (1883). 2 J. Sebelien, ibid. 9. 445 (1885). 



3 Tolmatscheff, Hoppe-Seyler's Medizin.-chem. Untersuchungen, p. 272 (1867). 



4 K. Storch, Monatsh.f. Chem, 18. 244 (1897). 



5 Fr. Alexander, Zeitschr, J. physiol. Chem. 25. 411 (1898). 



6 A. Scblossmann, ibid. 22. 197 (1896) ; compare also G. Simon, ibid. 33. 466 

 (1901). 7 E. Laqueur and O. Sackur, Hofmeister's Beitriige, 3. 193 (1902). 



8 0. Hammarsten, Maly's Jahresber. 4. 135 (1874). 



9 W. D. Halliburton, Journ. of Physiol. 11. 448 (1890). 



10 W. Cronheim and E. Miiller, Jahrbvchf. Kmderheilkunde, N.F. 47. 45 (1902) ; 

 H. Conradi, M unchener medizin. Wochenschr. 1901, p. 175. 



