10 



BULLETIN 98, XT. S. DEPARTMENT OF AGRICULTURE. 



SPECIFIC GRAVITY OF MILK AND CREAM. 



Table ILT covers the specific gravity of milk and cream determined 

 at 68° F. (20° C.) in terms of water at the same temperature as unity. 



Table III. — Specific gravity of milk and cream corresponding to various percentages of 



butter fat at 68° F. 



Per- 

 centage 

 of fat. 



Specific 



gravity. 



Per- 

 centage 

 of fat. 



Specific 

 gravity. 



Per- 

 centage 

 of fat. 



Specific 

 gravity. 



Per- 

 centage 

 of fat. 



Specific 

 gravity. 



0.025 

 1 

 2 



3 

 4 

 5 

 6 

 7 

 8 

 9 

 10 



1.037 

 1.036 

 1.035 

 1.034 

 1.032 

 1.031 

 1.030 

 1.029 

 1.027 

 1.026 

 1.025 



11 

 12 

 13 

 14 

 15 

 16 

 17 

 18 

 19 

 20 



1.024 

 1.022 

 1.020 

 1.019 

 1.018 

 1.017 

 1.016 

 1.015 

 1.014 

 1.013 



21 

 22 

 23 

 24 

 25 

 26 

 27 

 28 

 29 

 30 



1.012 

 1.011 



1.010 

 1.009 

 1.008 

 1.008 

 1.007 

 1.006 

 1.005 

 1.004 



31 

 32 



33 

 34 

 35 

 36 

 37 

 38 

 39 

 40 



1.003 



1.002 



1.001 



1.000 



.999 



.999 



.998 



.997 



.996 



.995 



FREEZING POINT OF MILK. 



The freezing point of milk depends upon its composition, but is 

 always lower than that of water. The freezing point of market milk 

 generally varies from 31° to 29° F. The addition of water to milk 

 serves to raise the freezing point toward that of pure water, 32° F., 

 while, on the other hand, the addition of fats, solids, etc., tends to 

 lower the freezing point, as does also the increase in acidity. Upon 

 these variations in the freezing point is based the cryoscopical method 

 of determining the addition of water to milk. 



EFFFECT OF FREEZING ON MILK. 



While the action of cold on milk at a temperature above the freezing 

 point has no other effect than that of varying the density and vis- 

 cosity, at a temperature below the freezing point it changes the 

 chemical and physical composition. 



According to Kasdorf, 1 when raw milk which was partly frozen 

 at a temperature of 10.5° F., in the ordinary container, during trans- 

 portation, it was found that ice first formed around the sides and at 

 the bottom of the can; the central core contained most of the casein, 

 sugar, and other mineral ingredients, while most of the fat was found 

 in the top layer of the liquid portion. 



■When milk has been frozen gradually, without agitation, and thawed 

 out clots will be found floating in the liquid, composed mostly of 

 albumen and fat, which may be dissolved by cooking; on the other 

 hand, if the milk is preserved in a frozen condition for three or four 

 weeks these clots will be very hard to dissolve, and the difficulty 

 experienced in dissolving them increases as the length of time the 



i Kasdorf, Otto. Eis und Kalte in Molkereibetrieb. Leipzig, 1904, p. 20. 



