DETERMINATION OF ALBUMENOID NITROGEN. 49 



Previous to the precipitation of the albuminoid sub- 

 stances with Stutzer's reagent the milk must be treated 

 with alum solution to decompose the alkaline phos- 

 phates contained. Otherwise in the presence of cupric 

 hydroxide these phosphates suffer decomposition in 

 which copper phosphate and free alkali are formed. This 

 latter will then dissolve the albuminoids and render the 

 estimation inexact. By the addition of alum this objec- 

 tionable reaction of the alkaline phosphates is prevented 

 owing to the formation of alkaline sulphates and insolu- 

 ble aluminum phosphates. 



For the analysis by this process lo c. c. of milk are 

 placed in a 250 c. c. beaker and diluted with 100 c. c. 

 water (for human milk 60 c. c. water are used). The mix- 

 ture is then heated nearly to boiling, 2 c. c. of saturated 

 alum solution are added and when the fluid begins to 

 boil 5 c. c. of Stutzer's reagent are run in and the mix- 

 ture kept at the boiling point for five minutes. The re- 

 sulting precipitate which settles quickly is washed with 

 hot water until the filtrate shows no reaction for sul- 

 phuric acid (the addition of barium chloride to a few 

 drops of the filtrate acidified with hydrochloric acid 

 should produce no turbidity). The filter and contents 

 are then placed in a Kjeldahl flask and treated in the 

 usual manner. 



The reaction of the diluted milk should be noticed be- 

 fore adding the copper reagent. If it be alkaline it should 

 be exactly neutralized by the careful addition of alum 

 since free alkali as mentioned above, dissolves the al- 

 buminoids and consequently prevents the precipitation 

 b\- the copper hydroxide. From the nitrogen content 

 thus determined the percentage of albuminoids may be 

 calculated according to the formula given. 

 J. Precipitation -xith Triohloracetic acid {Bondsczin- 



sky). 



