244 REPoRT OF THE CHEMIST OF THE 
phate. Eugling* held that casein enters into combination with- 
tricalcium phosphate, and the same view was held by Schaffer.’ 
Sé6ldner® showed that casein prepared from cows’ milk can form 
two calcium salts, (1) a basic calcium casein, containing about 
2.36 per ct. of CaO, neutral to phenolphthalein, but alkaline to 
litmus, and (2) a neutral calcium caesin, containing about 1.55 
per ct. of CaO, slightly acid to phenolpthalein and neutral 
or slightly alkaline to litmus. Sé6ldner believed that this neutral 
calcium casein is probably the form existing in milk, owing to its 
reaction and to its coagulability by rennet in the presence of 
soluble calcium salts. He also held that the calcium phosphate, 
usually found in casein precipitates, exists in a condition of 
suspended particles finely divided, and not in chemical combi- 
nation with casein. Courant’ confirmed the work of Sdéldner, 
calling the basic compound tri-calcium casein, and the neutral 
compound di-calcium casein. He also reported on rather intan- 
gible evidence a mono-calcium casein, the existence of which has 
not been confirmed and appears doubtful. He regards milk-casein 
as made up partly of di-, and partly of mono-, calcium casein. 
Courant’s work was entirely volumetric and no attempt was made 
to isolate the individual compounds. Lehman and Hempel? 
regard milk-casein as a double compound formed by the combi- 
nation of calcium casein and calcium phosphate. 
The work done by us confirms that of Sdldner. While he 
carried on his work mostly by volumetric methods, we have suc- 
ceeded in isolating the two calcium casein compounds described by 
him. The details of our work follow. 
Preparation of casein.—We prepared casein from cows’ milk by 
Hammarsten’s method, repeating the precipitation and solution 
four times. The precipitate was finally dissolved in 20 liters of 
very dilute ammonia water and precipitated by dilute acetic acid. 
The precipitate was ground in a mortar several times with water, 
then with alcohol, after which it was treated with ether and dried 
at 100° C. Ths prepared, the casein was practically ash-free, 
* Maly Jahresber, d. Thierchem., 4:146 (1874). 
4 Landw. Versuchs-Sta. 31:392 (1885). 
5 Landw. Jahrb. d. Schweiz., 1:33 (1887). 
6 Landw. Versuchs-Sta., 35:351 (1888). 
7 Pfliiger’s Arch., 50:109 (1891). 
® Pfliiger’s Arch., 56:558 (1894). 
