Casein and its Primary Cleavage Products. 363 
wholly remove the inorganic salts, and thus recourse was had to 
repeated precipitation by acids, after solution in dilute alkalies. By 
this method, Hammarsten* came to the conclusion that milk con- 
tains but two albuminous bodies, viz: casein and lacto-albumin, and 
the same investigator has repeatedly made use of this method for the 
preparation of pure casein. Lundbergt has plainly shown the notice- 
able resistance of casein to the action of acids, and Hammarsten has 
indicated the possibility of using acetic acid, if necessary, in place 
of the stronger hydrochloric acid. Millon and Commaille, however, 
have claimed that in the precipitation of casein with either acid, the’ 
precipitate does not consist of free casein, but is a compound of 
casein with the acid used. 
This erroneous view, Hammarsten shows depends simply on the 
great difficulty of washing the precipitated casein completely, and 
he suggests that it is perhaps impossible to prepare large quantities 
of casein absolutely pure. For the preparation of the substance, 
however, Hammarsten recommends acetic acid in preference to 
hydrochloric acid and final drying of the compound at a temperature 
of FL0°°C. 
Danilewsky and Radenhausen,} however, prefer to use hydrochloric 
acid in the preparation of pure casein, and for this purpose they use 
skimmed milk, diluted with 4-5 volumes of water, to which the dilute 
acid is added little by little, until a good precipitate is obtained. 
After filtration and repeated washing with distilled water, the casein 
is rubbed fine, then dissolved in water to which a little ammonia 
has been added, the fluid filtered and the clear filtrate again precipi- 
tated by the addition of a little dilute hydrochloric acid. Casein, so 
prepared, after being washed with distilled water, reacts acid to test 
papers and shows the usual reactions of this body; but if when 
freshly precipitated, the substance is boiled with perfectly neutral 
50 per cent. alcohol and filtered hot, according to Danilewsky and 
Radenhausen, the casein is separated into two bodies, one of which 
is partially soluble in hot alcohol and separates out on cooling, while 
the other is insoluble. The soluble portion is termed caseoprotalbin, 
the insoluble portion caseoalbumin. The former, it is stated, gives 
* Zur Kenntniss des Caseins und der Wirkung des Labfermentes, Jahresbericht 
fir Thierchemie, 1877, p. 158. 
+ Kleinere Beitrage zur Kenntniss des Caseins, Jahresbericht fiir Thierchemie, 
1876, p. 11. 
¢ Untersuchungen tber die Kiweisstoffe der Milch, Jahresbericht fiir Thierchemie, 
1880, p. 186, 
