346 Cuemicay Tests AND ANALYSES 
increasing the heat gradually until frothing ceases. Digest for a 
time after the mixture is colorless, or nearly so, or until oxidation 
is complete. Do not add either potassium permanganate or 
potassium sulphid. Dilute, neutralize, distil and titrate with stand- 
ard alkah. In neutralizing, it is convenient to add a few drops 
of phenolphthalein indicator, by which one can tell, when the acid 
is completely neutralized, remembering that the pink color, which 
indicates an alkaline reaction, is destroyed by a considerable excess 
of strong fixed alkali. 
Casein and Albumin. 
“(a) Casein.—The determination should be made when the 
milk is fresh, or nearly so. When it is not practicable to make this 
determination within twenty-four hours, add one part of formal- 
dehyde to twenty-five hundred parts of milk and keep in a cool 
place. Place about 10 grams of milk in a beaker with about 90 c.c. 
of water at 40 degrees to 42 degrees C., and add at once 1.5 c.c. of 
a 10 per cent acetic acid solution. Stir with a glass rod and let 
stand from three to five minutes longer. Then decant or filter, wash 
two or three times with cold water by decantation and transfer pre- 
cipitate completely to filter. Wash once or twice on filter. The 
filtrate should be clear, or nearly so. If it be not clear when it first 
runs through, it can generally be made so by two or three repeated 
filtrations, after which the washing of the precipitate can be com- 
pleted. Determine nitrogen in the washed precipitate and filter by 
the Gunning method. ‘To calculate the equivalent amount of casein 
from the nitrogen multiply by 6.38. 
In working with milk which has been kept with preservatives, 
the acetic acid should be added in small proportions, a few drops 
at a time, with stirring, and the addition continued until the liquid 
above the precipitate becomes clear or very nearly so, 
(b) Albumin.—I'xactly neutralize with caustic alkali the fil- 
trate obtained in the preceding operation (a), add 0.3 ¢.c. of a 10 
per cent solution of acetic acid and heat the liquid. to the tempera- 
ture of boiling water until the albumin is completely precipitated, 
collect the precipitate on a filter, wash and determine the nitrogen 
’ 
therein. Nitrogen multiplied by 6.38 equals albumin,” or 
