84 MILK AND DAIRY PRODUCTS PART 



without previously being dried, and the nitrogen contained in 

 the filter deducted from the total. 



The amount of non-protein nitrogenous substances can be 

 determined either by evaporating the filtrate in a Hoffmeister 

 basin made of thin glass, and then breaking this up and 

 estimating the nitrogen by Kjeldahl's method, or, indirectly, by 

 deducting the nitrogen found as protein from the total nitrogen. 



(c) Sebelien's Method for Estimating the Total Protein. 



According to this method, 1 3-5 g. milk are diluted with two 

 or three volumes of water, a little common salt solution added, 

 and then tannic acid. 2 The precipitate which falls is washed 

 with cold water and the nitrogen in it determined in the usual 

 way by Kjeldahl's method. Multiplication of the nitrogen by 

 6'37 gives the protein. This method, which is easy to carry 

 out, gives very good results. 



2. Estimation of Casein. 



The method generally recommended for estimating the casein 

 in milk is to dilute it with water and then precipitate the 

 casein with small quantities of acetic acid, and weigh the dry 

 fat-free material. 



Ten to twenty grams are diluted with ten times the quantity 

 of water, warmed to a temperature not exceeding 40 C., and 

 a few drops of acetic acid added. The coagulated casein 

 is then brought on to a dry weighed filter and washed with 

 water, alcohol, and ether as described above, dried, and 

 weighed. 



This method is not, however, very accurate, because it is never 

 certain whether the acetic acid will precipitate the casein 

 quantitatively. The following procedure, due to Sebelien, is 

 more reliable: A weighed quantity of milk is diluted with 

 an equal volume of a saturated solution of magnesium 

 sulphate, and then solid magnesium sulphate added, until 

 the whole is saturated. The liquid is then filtered off, the 



1 ZeitscJirift fiir physioL Chemie, Vol. XIII. 



2 Almen's reagent 4 g. nitrogen-free tannic acid +190 c.c. 50% alcohol + 

 8 c.c. 25% acetic acid may be used. 



