MILK, BLOOD AND URINE 21 5 



Analysis of American milk by the Vermont Experiment 

 Station in 1890 gave the f oho wing results: 



Total solids, p. c. . 11. 35 ii-77 12.21 12.75 i3-i7 i3-7i I4-2S 14-77 I5-I7 iS-83 



Fat, p. c 3-20 3.36 3.60 3.82 4.09 4.46 4.87 5.20 5. 47 5.88 



Protein, p. c. . . . 2.99 3.03 3.10 3.29 3.40 3.48 3.65 3.87 4-07 426 



Sugar and ash, p. c. . 5.16 5.38 5.51 5.64 5.68 5.77 5.73 5.70 5.63 5.69 



Analysis 



The determination of the specific gravity and the composi- 

 tion of milk is usually carried out by different methods in the 

 chemical laboratory and in the dairy or creamery. The specific 

 gravity is the weight of a volume of milk compared with the 

 weight of an equal volume of water both at the same tempera- 

 ture or at definitely stated temperatures for each. In the 

 laboratory this is determined by direct weighing. In the dairy, 

 and also in the laboratory, it is usually made by the use of an 

 hydrometer spindle graduated especially for use with milk. 

 Such a hydrometer is called a lactometer. It may also be deter- 

 mined by means of a Westphal balance. 



The total solids in milk are determined by evaporation and 

 then weighing the dry residue. As the specific gravity varies 

 with the total solids it is possible to calculate the latter from 

 the former if the fat content is also known. A formula that 

 has been worked out for use with direct Quevenne lactometer 

 readings is as follows : 



rr. . 1 ^'^ lactometer reading , / .. r <t 4.\ 



Total solids = s + (1.2 X fat per cent) 



4 



The ash is determined by incinerating the dry residue or 

 total solids at a low red heat and weighing the remaining ash. 

 The proteins are determined by means of the Kjeldahl method 

 for nitrogen as given under proteins (p. 93). A creamery 

 method by means of the centrifuge has also been devised by 

 Hart for determining milk casein. Fats are determined by 

 extraction or by the Babcock method, as stated under milk 

 fats. The determination of milk sugar may be made in the 



