DETERMINATION OF PROTEIN 199 



sugar, NaCl, and other matter soluble in water, and the 



amount of common salt is then estimated in the solution 



N 

 by direct titration with — silver-nitrate solution, using 



a few drops of potassium chromate as indicator. One c.c. 



N . . 



— silver nitrate is equivalent to -00585 gram NaCl. 



(The approximate percentage of casein in the butter 

 may be obtained by drying and weighing the filter 

 paper after washing with water, and subtracting from 

 this weight the known weight of the filter paper.) 



191. Determination of Protein. 



The total protein in butter may be best determined 

 by the ordinary Kjeldahl process after removal of the 

 majority of the fat, as this substance is liable to cause 

 excessive frothing. 



About 20 grams of butter in a porcelain basin 

 should be treated with ether according to the method 

 described above (see 189, p. 198) for the estimation of 

 total solids not fat, and the residue washed on to a 

 filter paper as before. 



The filter and contents are then heated in a Kjeldahl 

 flask with 15 c.c. of concentrated HgSO^, and the opera- 

 tion completed as usual (see p. 10). The percentage 

 of nitrogen multiplied by 6-38 will give the percentage 

 of protein in the butter. 



Reichert-Meissl Number. 



Butter-fat is a mixture of the glycerides of a number of different 

 fatty acids (see p. 184), and differs from other fats, such as those 

 that might be employed to adulterate it, by reason of the fact that 

 a considerable proportion of the fatty acids combined with the 

 glycerine are of low molecular weight, and readily volatile in 

 steam. These facts are made use of for the detection of adultera- 

 tion with other fats, the presence of which will generally tend to 



