MILK 



81 



DR.ROB. MUENCKE 

 BERLIN. N.W. 



protein can be easily, and for most purposes sufficiently 

 accurately, estimated. 



About 10 g. of milk are weighed from a small covered beaker, 

 or flask provided with a stopper, into the usual Kjeldahl flask 

 of about 300 c.c. capacity. Then 15 c.c. of concentrated sul- 

 phuric acid and a drop of mercury or a little powdered copper 

 oxide are added. To allow of the addition of the same quantity 

 of mercury in each test, Dr. R. 

 Muencke, 1 of Berlin, has designed a 

 small piece of apparatus, a sketch of 

 which is seen in Fig. 45. 



At the commencement the Kjel- 

 dahl flask should only be heated 

 gently, but when the water has 

 evaporated the flame can be raised. 

 The heating must be continued until 

 the liquid is quite clear (if mercury 

 has been added) or bright green (if 

 copper oxide has been used) ; there 

 should be no black particles visible. 

 All the organic nitrogen has now 

 been converted into ammonium sul- 

 phate, and the contents of the Kjel- 

 dahl flask can be poured into a larger 

 distillation flask, the former being 

 afterwards well rinsed out. To the liquid in the distillation 

 flask there is now added 25-30 per cent, of caustic soda or 

 caustic potash solution (the alkali should have been purified 

 by alcohol) until the reaction becomes alkaline, and also enough 

 potassium sulphide solution 2 (40 g. potassium sulphide per 

 litre) to precipitate the mercury as sulphide, which gives a 

 black colour to the liquid. Finally, a little zinc dust is added, 

 and the flask connected immediately to the distillation 

 apparatus, of which there are many forms, one being shown 

 in Fig. 46. 



On distillation, the ammonia which has been liberated by 

 the alkali passes over and is led into a flask containing a known 



1 Luisenstrasse, 58. 



2 If CuO has been used instead of Hg, the addition of K 2 S is, of course, 

 unnecessary. 



G 



FIG. 45. Apparatus for 

 Measuring Mercury. 



