THE CHEMICAL COMPOSITION OF MILK 



33 



compared with serum obtained from whey which had been 

 obtained from another portion of the same milk by treatment 

 with rennet-extract. In the second experiment, serum direct 

 from fresh milk was compared with (a) serum obtained from 

 another portion of the same milk after souring, and (b) serum 

 obtained from another portion of the same milk to which some 

 formaldehyde solution had been added. Albumin was deter- 

 mined in each case by boiling after addition of acetic acid, 

 following the details given in the provisional method of the 

 Association of Official Agricultural Chemists. The results of 

 the experiments are given below. 



First Experiment 



Albumin per 100 C.C. 



Albumin op Milk Re- 

 covered in Serum 



Fresh milk 



Serum, from fresh milk . . . 

 Serum from whey . . . . 



Second Experiment 



Fresh milk 



Serum from fresh milk ... 

 Serum from sour milk 

 Serum from milk plus formalde- 

 hyde 



grams 



0.312 

 0.143 

 0.187 



0.266 

 0.148 

 0.253 



0.245 



/ 



per ct. 



45.83 

 59.94 



55.64 

 95.11 



92.21 



In the first experiment it is seen that when casein is precipi- 

 tated by rennet solution the curd (the precipitated casein or 

 para-casein) carries down part of the albumin with it; the 

 amount thus carried down is approximately equal in this case 

 to that retained along with the casein on the external surface 

 of the Pasteur-Chamberland filtering tube, when whole milk 

 is filtered through such a filter. 



In the second experiment we see that when the casein is pre- 

 cipitated with acid, as in the case of natural souring, the ad- 



