CASEINE. 



29 



say 50 or 100 c. c. of milk and, without any preliminary 

 evaporation to dryness, precipitating the caseine, which is to 

 be washed with water, alcohol, and ether, and then to be 

 dried and weighed. The precipitation is effected by warm- 

 ing the milk, and acidulating it with almost any common 

 acid ; either hydrochloric or sulphuric, or even ascetic acid 

 will do. As aforesaid, I do not like that modification so well 

 as the one first given. 



A very different method of determining caseine in milk 

 consists in measuring it by the albuminoid ammonia which 

 it is capable of furnishing. This is certainly the quickest 

 process, and is very satisfactory. 



In order to practise it, the milk must first be diluted with 

 a known volume of water, so that one volume of dilute milk 

 may contain accurately y^ of a volume of milk. This is 

 conveniently accomplished by measuring out with the pipette 

 10 c. c. of milk, and dropping it into the litre flask, which is 

 subsequently filled up to the litre mark. Or, of course, 5 

 c. c. of milk may be diluted to 5-0 c. c. 



It is not necessary to use distilled water for the purpose, 

 inasmuch as the error introduced by ordinary river or town 

 water is inappreciable. The quantity of the diluted milk 

 which is required for experiment is 5 or 10 cubic centimetres, 

 equivalent to ^-^ or yL ^ of a cubic centimetre of real milk. 



The mode of operation is as follows : 



Ten grammes of solid potash and 0.4 gramme of crystals 

 of permanganate of potash are boiled with about half a litre 

 of water, the whole being contained by a retort provided 

 with a tubulure, and connected with a Liebig's condenser. 

 The liquid is allowed to distil, and successive portions of 

 distillate tested for ammonia. So soon as water begins to 

 distil over in a state of freedom from ammonia, the portion of 

 diluted milk is to be introduced into the retort through the 

 tubulure. 



