224 Testing Milk and Its Products. 



the watery solution of ammonia sutfate 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^ 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.^ 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 oo. of milk (aa obtained in deter- 

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

 ard HCl 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. J^ 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 ce. semi-normal HCl-solution corresponds to 

 7 milligrams or .007 gram of nitrogen; 4.67 cc. -^ HCl 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 xi go_^g3g ^^^ ^^^^^ ^^ nitrogen, and 

 . 635X6. 25;=3. 97 per cent, of casein and albumen. 



' 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). 



