ESTIMATION OF CASEIN. 131 



small quantity of acetic acid ; it is collected on a tared filter and 

 weighed as such. 



In order to avoid the tedious washing with a saturated solu- 

 tion of magnesium sulphate, LefEmann and Beam take a larger 

 quantity of milk (say 20 grammes), dilute with twice its bulk of 

 saturated magnesium sulphate solution, add powdered magnesium 

 sulphate till saturated, and make up to a definite volimie with 

 saturated magnesium sulphate solution in a graduated cylinder. 

 The solution is allowed to stand and the lower clear portion is 

 removed by a pipette ; this is filtered and an aliquot poi-tion 

 taken ; the albumin is estimated in this, as directed above. 

 The casein is determined by subtracting the albumin nitrogen 

 from the total nitrogen and multiplying the diSerence by 6 '.38. 



Sodium chloride, to which a little calcium chloride has been 

 added, can be substituted for magnesium sulphate ; the preci- 

 pitate is less easy to treat, owing to the formation of hydrogen 

 chloride on heating the precipitate with sulphuric acid. 



Estimation of Casein. — Lehmann's Method. — Lehmann 

 has devised a method for the estimation of casein in milk by 

 means of unglazed porcelain plates ; the plate is wetted with 

 water, and 5 grammes of milk diluted with 5 grammes of water 

 placed in the centre. After about an hour and a half the serum 

 is separated, and the casein, together with the fat, is removed 

 with a spatula ; the last traces of casein are removed by setting 

 the plate in water. The fat is removed by extraction with 

 ether, the casein being ground up to extract the last traces ; the 

 casein is dried at 100° C. on a weighed filter, and weighed ; 

 from the weight is deducted the weight of the ash left on 

 incineration. 



The results are said to be very accurate. The casein is 

 obtained in the state in which it exists in the milk. 



Schlossman's Method. — Schlossman proposes to estimate 

 casein by warming 10 c.c. of milk mixed with 3 to 5 parts of 

 water to 40°, and adding 1 c.c. of a concentrated solution of 

 alum. Should the flocculent precipitate not subside rapidly an 

 additional 05 c.c. of alum solution may be added, since a slight 

 excess (up to 1 c.c.) does not afiect the results. The precipitate 

 is allowed to stand for some minutes, and is then filtered. After 

 having been washed with water and dried, the filter and its 

 contents are extracted with ether in a Soxhlet extractor (an 

 estimation of fat being thereby obtained) ; the nitrogen deter- 

 mined by Kjeldahl's method, and multiplied by 6'38, gives the 

 weight of the casein. 



Richmond's Method. — The albumin in milk, which has been 

 raised to the boiling point, behaves with all methods as casein. 

 An approximate estimation of real casein in milk, which has been 



