CASEIN. 21 



applied cautiously, as casein is soluble in an excess of many 

 acids. 



On the addition of ferrocyanide or ferridcyanide of potassium 

 to a perfectljr neutral solution of casein, a slight precipitate is 

 observed ; if the solution is alkaline there is no perceptible effect, 

 but if it is first rendered acid by a little acetic or dilute sul- 

 phuric acid, a copious precipitate is thrown down by both tests. 



The casein of cow's milk is thoroughly precipitated by the 

 mucous membrane of the calf's stomach ; on the addition of this 

 reagent to woman's milk, imperfect coagulation sometimes oc- 

 curs ; in other cases no apparent action is produced ; the coagu- 

 lation is never perfect. In this case the mucous membrane of 

 the child's stomach produces a more energetic effect than that 

 of the calf. If a quantity of potash or ammonia be added to 

 the milk, sufficient to give it a decidedly alkaUne reaction, no 

 coagidation is effected. 



Rochleder has recently attempted to show that pure casein 

 is a substance nearly insoluble in water ; that the so-called 

 soluble casein is a combination of casein with potash, soda, 

 or lime ; and that the coagulation of the soluble casein by acids 

 is nothing more than a separation of the casein, resulting from 

 the combination of the acid Avith the base of the casein com- 

 pound. In this manner, he explains how solutions of potash 

 prevent coagulation, when added in very small quantity to milk, 

 and why (especially in warm weather) very slight causes are 

 able to produce a coagulation of the milk ; as only the smallest 

 quantity of lactic acid is required to be formed, in order to 

 neutralize the minute traces of soda, which are able to retain 

 in a state of solution an enormous quantity of casein. 



Coagiilated casein is found in the milk, constituting the walls 

 of the butter-vesicles. For the purpose of chemical investiga- 

 tion, it is best obtained by the addition of anhydrous alcohol 

 to a solution of casein. When dried, it is hard, yellow, and 

 transparent. In its chemical relations it closely resembles coagu- 

 lated albumen. 



The amount of ash left after the incineration of casein seems 

 to vary considerably. Mulder estimates it at 3*85, and Simon 

 at 7^, in the casein of cow's milk. In casein from the milk of 

 woman, Simon estimated it at 5'^^. Uochleder, whose experi- 

 ments were made under the direction of Liebig, found that pure 



