PROPERTIES OF MILK. 13 



is explained by the fact that milk-sugar undergoes incipient decomposi- 

 tion, producing small quantities of yellow and brown substances (lacto- 

 caramel 1). Continuous heating affects the fineness of the state of division 

 of the fat of the milk. The microscopically small fatty globules become 

 partly dissolved and run together, forming large drops of fat easily visible 

 to the naked eye. The boiling point of milk is a fraction of a degree 

 higher, and the freezing point a fraction of a degree lower, than the 

 boiling and freezing points of water. The maximum density point of 

 milk is not 4*08 C., as is the case with water, but - -3 C. Possibly these 

 conditions vary with the percentage of solids in the milk, especially of fat, 

 but no 'experiments have been made on this point. The behaviour of 

 milk under the influence of the electric current also requires investigation. 

 The question of how far electricity might be beneficially applied in dairy- 

 ing still awaits investigation. 



The coefficient of expansion of milk increases with the temperature, 

 as well as with the percentage of total solids, and, between the tempera- 

 tures of 5 and 15 C., is undoubtedly greater than that of water. It 

 follows from this that milk loses more and more of its limpidity as the 

 temperature is reduced, and at temperatures below 10 C. it assumes a 

 slightly viscous condition, and maintains this viscosity on its surface. 

 According to experiments by the author, the variation in the volume of 

 ordinary cows' milk (of a specific gravity 1-0315 at 15 C.) at different 

 temperatures is as f ollows : 



1,000,000 volumes at C. 



1,000,030 1 C. 



1,000,391 4 C. 



1,001,273 10 C. 



1,002,134 15 C. 



1,003,800 20 C. 



1,006,414 30 C. 



1,014,277 50 C. 



1,019,243 60 C. 



The absorptive capacity of milk for heat (latent heat) is not a constant 

 quantity, but depends, according to experiments carried out by the author 

 in 1874, on the quantity of total solids. For milk of ordinary chemical 

 composition it may be stated at *847, water being taken as 1 '000. 



When exposed to the action of frost the larger portion of the milk 

 is frozen, a small portion only remaining liquid. The portion remaining 

 liquid is richer in solid matter than the portion frozen. 



When milk is subjected to dialysis only a portion of the mineral mattei 

 and the milk-sugar diffuse through, and possibly also a trace of nitrogenous 

 matter. 



