PHYSICAL AND CHEMICAL EXAMINATION OF MILK 181 



phosphate are dissolved in dilute hydrochloric acid and the iron 

 determined colorimetrically as sulphid, ferrocyanid, or thiocyanate. 



"To estimate the alkalies, another portion of the milk is 

 ignited and the ash dissolved in dilute hydrochloric acid and 

 boiled. A few drops of barium chlorid solution are added to make 

 0.1 gram per 100 grams of milk and boiling continued for some 

 minutes. After some hours the precipitate of barium sulphate is 

 filtered off, ignited, and weighed. The weight multiplied by 

 0.34335 gives the sulphuric anhydrid in milk. Ferric chlorid 

 solution is added to color the solution brown and the filtrate made 

 alkaline with ammonia. The precipitate is well washed and the 

 filtrate evaporated and cautiously ignited. The weight gives the 

 alkaline chlorids. The residue is redissolved in water, and if the 

 solution is not quite clear, ammonium carbonate is added, the 

 liquid evaporated to dryness, and the residue cautiously ignited. 

 The residue is again taken up with water, filtered, and evaporated; 

 the residue is cautiously ignited and weighed. 



"Chlorin is titrated with standard silver nitrate solution with 

 potassium chromate as indicator. The potassium and sodium 

 are calculated as follows: 



"W. = weight of alkaline chlorids. 



"C. = weight of chlorin therein. 



"Weight of sodium = 2.997 C. 1.4254 W. 



"Weight of potassium = 2.4254 W. 3.997 C. 



"Potassium is directly estimated by evaporating the solution 

 of alkaline chlorids with excess of platinum tetrachlorid solution 

 almost to dryness. The pasty residue is treated with 80 per cent, 

 alcohol containing 5 per cent, ether and washed repeatedly with 

 this mixture. The alcohol is passed through a weighed filter or 

 a Gooch crucible, and the precipitate finally transferred to this 

 and washed with ether. It is then dried at 100 C. and weighed. 

 The weight multiplied by 0.3056 gives potassium chlorid; this sub- 

 tracted from the weight of the alkaline chlorids gives sodium 

 chlorid. 



"Potassium chlorid multiplied by 0.5244 gives potassium, and 

 by 0.6314, potash. Sodium chlorid multiplied by 0.3932 gives 

 sodium, and by 0.5299, soda. 



"Magnesia Mixture. 100 grams magnesium chlorid are dis- 

 solved in water and ammonia added until the solution smells 

 strongly of ammonia. Then enough ammonium chlorid is added 

 to dissolve the precipitate and the volume made up to 1 liter." 



DETERMINATION OF PROTEINS 



Determination of Total Nitrogen. The total nitrogen is best 

 determined by the Gunning method, which is carried out as fol- 



