210 Testing Milk and Its Products. 



Erlenmeyer flask, and the flask connected with a distilla- 

 tion apparatus. At the other end, the Jena flask con- 

 taining the watery solution of the ammonium sulfate is 

 connected, after adding 50 cc. of a concentrated soda 

 solution (1 pound "pure potash" dissolved in 500 cc. of 

 distilled water and allowed to settle); the contents of the 

 Jena flasks are now heated to boiling, and the distillation 

 is continued for forty minutes to an hour, until all 

 ammonia has been distilled over. 



The excess of acid in the Erlenmeyer receiving-flask 

 is then accurately titrated back by means of a tenth- 

 normal standard ammonia-solution, using a cochineal - 

 solution 1 as an indicator. From the amount of acid 

 used, the per cent, of nitrogen is obtained; and from it, 

 the per cent, of casein and albumen in the milk by multi- 

 plying by 6.25. 2 The amount of nitrogen contained in 

 the chemicals used is determined by blank experiments 

 and deducted from the nitrogen obtained as described. 



Example: The weight of 5 cc. of milk (as obtained in deter- 

 mining the water in the milk) was 5.1465 grams. 5 cc. of stand- 

 ard HC1 are added to the receiver, and 1.55 cc. of JQ alkali- 

 solution are used in titrating back the excess of acid. 1.55 cc. 



of alkali = ^-=.51 cc. ^ acid-solution; the ammonia dis- 

 tilled over therefore neutralized 5.00 .51=4.49 cc. acid. By 

 blank trials it was found that the reagents used furnish an 

 equivalent of .02 cc. acid in the distillate; this quantity sub- 

 tracted from the acid-equivalent of the nitrogen of the milk 

 leaves 4.47 cc. 1 cc. semi-normal HCl-solution corresponds to 



7 milligrams or .007 grams of nitrogen; 4.47 cc. HC1 therefore 



iSutton, Volumetric Analysis, 4th edition, p. 31. 



2 The factor 6.30 or 6.37 is more correct for the albuminoids of milk, but 

 has not yet been generally adopted, (p. 15, foot note). 



