XXII. DAIRY PRODUCTS. 



MILK. 



1 SOLIDS.— OFFICIAL. 



Heat 3-5 grams of the milk at the temperature of boiling water until it ceases 

 to lose weight, using a tared, flat-bottomed dish of not less than 5 cm. diameter. 

 If desired, previously place 15-20 grams of pure, dry sand in the dish. Cool in a 

 desiccator and weigh rapidly to avoid absorption of h3'groscopic moisture. 



2 ASH.— OFFICLAL. 



Weigh about 20 grams of the milk in a tared dish, add 6 cc. of nitric acid, evap- 

 orate to dryness and ignite at a temperature just below redness until the ash is free 

 from carbon. 



3 TOTAL NITROGEN.-OFFICL/^L. 



Place about 5 grams of the milk in a Kjeldahl digestion flask and proceed, without 

 evaporation, as directed under I, 18, 21 or 23. Multiply the percentage of nitro- 

 gen by 6.38 to obtain the equivalent percentage of nitrogen compounds. 



CASEIN. 



(This determination should be made while the milk is fresh, or nearly so. 



When it is not practicable to make this determination within 



24 hours, add 1 part of formaldehyde to 2500 



parts of milk and keep in a cool place.) 



4 Method I.— Official. 



Place 10 grams of the milk in a beaker with 90 cc. of water at 40°-42°C. and add 

 at once 1.5 cc. of 10% acetic acid. Stir and let stand 3-5 minutes. Then decant 

 on a filter, wash by decantation 2-3 times with cold water and transfer the precipi- 

 tate to the filter. Wash once or twice on the filter. The filtrate should be clear, 

 or very nearly so. If the first portions of the filtrate are not clear, repeat the fil- 

 tration, after which complete the washing of the precipitate. Determine nitrogen 

 in the washed precipitate and filter paper as directed under I, 18, 21 or 23, mul- 

 tiply by 6.3S and calculate the percentage of casein. 



In samples of milk which have been preserved, the acetic acid should be added 

 in small portions, a few drops at a time, with stirring, and the addition continued 

 until the liquid above the precipitate becomes clear, or very nearly so. 



5 Method II.— Official. 



To 10 grams of the milk add 50 cc. of water at 40°C., then 2 cc. of alum solution 

 saturated at 40°C., or higher. Allow the precipitate to settle, transfer to a filter 

 and wash with cold water.' Determine nitrogen in the precipitate and filter paper 

 as directed under I, 18, 21 or 23, multiply by 6. .38 and calculate the percent- 

 age of casein. 



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