20 MILK ANALYSIS 



Strong Sodium Hydroxid Solution. 500 grams should be 

 added to 500 c.c. of water, the mixture allowed to stand until 

 the undissolved matter settles, the clear liquor decanted and 

 kept in a stoppered bottle. It will be an advantage to de- 

 termine approximately the quantity of this solution required 

 to neutralize 20 c.c. of the strong sulfuric acid. 



Indicator. Cochineal solution is recommended by the A. 

 O. A. C., but methyl-orange is satisfactory. Phenolphthalein 

 is not well adapted to titration of ammonium compounds. 



Digestion Flasks. Pear-shaped round-bottomed flasks of 

 hard, moderately thick, well-annealed glass, about 22 cm. 

 long, maximum diameter of 6 cm., tapering gradually to a 

 long neck, 2 cm. in diameter at the narrowest part, and slightly 

 flared at the mouth. 



Distillation Flasks. Jena-glass flasks of about 550 c.c. ca- 

 pacity. A copper flask, such as sometimes used in the manu- 

 facture of oxygen, may be substituted. 



Combined Digestion and Distillation Flasks. Jena- glass 

 round-bottomed flasks with a bulb 12.5 cm. long and 9 cm. in 

 diameter, the neck cylindrical, 15 cm. long and 3 cm. in di- 

 ameter, flared slightly at the mouth. 



Process. 5 c.c. of the sample are placed in a digestion flask, 

 10 grams of powdered potassium sulfate and 15 to 25 c.c. 

 (ordinarily about 20 c.c.) of the strong sulfuric acid are added 

 and the digestion conducted as follows: The flask is placed 

 in an inclined position and heated below the boiling-point of 

 the acid for from five to fifteen minutes, or until frothing has 

 ceased. Excessive frothing may be prevented by the addi- 

 tion of a small piece of paraffin. The heat is raised until the 

 acid boils briskly. A small, short-stemmed funnel may be 

 placed in the mouth of the flask to restrict the circulation of 

 air. No further attention is required until the liquid has 

 become clear and colorless, or not deeper than a pale straw. 



When Kjeldahl operations are carried out in limited number, 



