224 Testing Milk and Its Products. 



the watery solution of ammonia 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 mixed and 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 mul- 

 tiplying 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 ~- alkali 

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

 of alkali = =.31 cc. -y- acid solution; the ammonia dis- 

 tilled over therefore neutralized 5.00 .31=4.69 cc. acid. By 

 blank trials it was found that the reagents used furnished an 

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

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

 leaves 4.67 cc. 1 cc. semi-normal HCl-solution corresponds to 

 7 milligrams or .007 gram of nitrogen ; 4.67 cc. HC1 therefore 

 represents .03269 gram of nitrogen. This quantity of nitrogen 

 was obtained from the 5.1465 grams of milk measured out; the 

 milk therefore contains - 03269 * 1QO .635 per cent, of nitrogen, and 

 .635X6.25=3.97 per cent, of casein and albumen. 



1 Sutton, Volumetric Analysis, 4th edition, p. 31. 

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

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



