MILK. 293 



found in the milk they exist in the combinations from which 

 they are most readily assimilated. , 



The Colostrum. This is the milk secreted before and for 

 a few days after parturition, and is characterized by higher 

 specific gravity and content of solids. It contains a large 

 amount of coagulable proteins and therefore thickens on boil- 

 ing. Some idea of the general composition is given by the 

 following figures which represent the means of a number of 

 analyses : 



Per Cent 



Water 74-O5 



Casein 4-66 



Albumin 13.62 



Fat 3-43 



Sugar 2.66 



Salts 1.58 



Whey is the fluid left after separation of the larger part of the fat and 

 casein in the cheese industry or by analogous coagulation. The sugar and 

 salts remain practically unchanged, while the fat and casein are reduced to 

 traces. The lactalbumin left averages about 0.5 per cent. 



Buttermilk differs from ordinary milk essentially in its lower content 

 of fat. It is usually sour because of being separated from ripened cream, 

 and contains therefore an appreciable amount of lactic acid formed at the 

 expense of some of the sugar. 



Skimmed milk is in composition similar to buttermilk but is usually 

 sweet. In the modern methods of separation by centrifugal machines the 

 fat may be reduced to less than half of one per cent; the protein is also 

 somewhat reduced. 



SOME EXPERIMENTS WITH MILK. 



A few simple tests may be made to illustrate the composi- 

 tion of milk. 



THE TEST FOR FAT. Pour about 20 cc. of milk in a porcelain dish, add 

 an equal volume of clean, dry quartz sand and evaporate, with frequent 

 stirring, about an hour on the water-bath. Then loosen the dry mass as 

 well as possible by means of a spatula, or glass rod, and pour over it 25 cc. 

 of light benzine. Stir up well and cover with a sheet of paper and allow 

 to stand 15 minutes. Then pour the liquid through a small, dry filter into 

 a small, dry beaker, and place this in hot water to volatilize the benzine. 



A residue of fat will be left. Do not attempt to evaporate the benzine 

 over a flame, or on a water-bath under which a lamp is burning. Heat the 

 water, then extinguish the flame and immerse the vessel containing the 

 benzine in the hot water. 



