ADVANCED PHYSIOLOGICAL CHEMISTRY 439 



therefore, can be shown to contain phosphorus. If it be digested with 

 pepsin solution of the usual strength a certain amount of the proteid is 

 split off as peptone, and the sediment which settles down will be found 

 to contain a much higher percentage of phosphorus than the original 

 casein (for detection of this see p. 179). If, on the other hand, a strong 

 pepsin solution be employed, and the digestion be allowed to proceed 

 for several days, all the proteid will become changed into peptone, the 

 phosphorus partly separating as phosphates, and partly remaining in 

 organic combination with the albumoses and peptones which are 

 simultaneously formed. 



The Quantitative Determination of the various Bodies in Milk. 

 The methods here described can be employed for other fluids besides 

 milk. 



(1) The Percentage of Water. A weighed quantity of milk is mixed 

 with a weighed quantity of fine quartz sand, which has been previously 

 heated to redness and then cooled in a desiccator. The weight of the 

 mixture is accurately determined, and it is then placed in a hot air bath 

 heated to 100 C. until all the water has been driven off and the weight 

 is constant. The amount of weight lost corresponds to the amount of 

 water which the sample of milk contains. 



(2) The Percentage of Proteid. Three grs. of milk are diluted with 

 four times its volume of distilled water, a few c.c. of a solution of sodium 

 chloride are added, and then a solution of tannic acid until all the 

 proteid has been precipitated. The precipitate is filtered off through 

 an ash-free filter paper, and thoroughly washed with distilled water. 

 The filter paper with the precipitate is removed to a KjeldahTs com- 

 bustion flask, and the nitrogen estimated as described on p. 242. The 

 result multiplied by 6*37 gives the total amount of proteid contained in 

 the sample of milk. 



(3) The Percentage of Fat. The dietetic value of a milk depends 

 to a large extent on the amount of fat it contains. There are, therefore, 

 numerous methods employed for the quantitative estimation of this, 

 some of which are only approximate. The following method (Adam's) 

 will be found very simple and sufficiently accurate for most purposes : 



Measure 5 c.c. milk and drop it on to a strip of Adam's fat-free 

 porous paper ; l allow this to dry in the air bath at 60 C., then roll it 

 up and place it in the extractor of Soxhlet's apparatus (see p. 432). The 

 weight of the distilling flask is ascertained before beginning the 

 extraction, and then again after the extraction has been allowed to pro- 

 ceed for about one hour and the ether has been- distilled off; the 

 increase of weight g' v r es the amount of fat in 5 c.c. of milk. Sufficient 

 1 The paper can be obtained from any of the dealers. 



