44 



INTRODUCTORY — THE CONSTITUENTS OF MILK. 



The glyceroxide may act on alcohol forming ethoxide, instead 

 of on water forming hydroxide. 



Allen and Homfray have shown that by the action of a very 

 small quantity of caustic soda on acetin (glyceryl tri-acetate), 

 in the presence of alcohol, a very large proportion of ethyl acetate 

 is formed, many molecules of ethyl acetate being produced by 

 each molecule of sodium ethoxide ; this can only be explained 

 by the action shown iu equation (iv.). 



Duffy has shown that ethyl and amyl stearate may be pro- 

 duced from glyceryl stearate and sodium ethoxide and amoxide 

 respectively. 



The action of sodium ethoxide on milk fat has a practical 

 bearing on butter analysis, owing to the volatility of ethyl buty- 

 rate, which, unless precautions are taken, is liable to cause loss 

 of butyric acid on saponification. 



From their sodium salts the acids may be set at liberty by the 

 addition of a mineral acid. 



Properties. — ililk fat is insoluble in water, but dissolves about 

 0'2 per cent, of this substance. It is not volatile, though when 

 heated to 100° C. a loss of weight is noticed owing to the dis- 

 solved water being volatilised. On further heating at this tem- 

 perature, in a current of hydrogeil, no change is noticed ; but if 

 oxygen be allowed access a gradual increase of weight, due to 

 oxidation, is found ; if the heating be prolonged, say for a week, 

 the weight again decreases, and profound changes, the nature 

 of which has not been elucidated, take place. 



Solid and Liquid Portions. — The fat of milk being ■ an 

 undoubted mixture has no sharply defined melting point. If 

 rapidly cooled to a low temperature it becomes solid, and melts 

 on warming at from 29 '5° to 33° C. By slow cooling it does not 

 solidify as a whole, but behaves as a solution of fat of a high 

 melting point in fat of a low melting point. 



The author obtained the following figures (Table II.) by 

 allowing a sample to cool down gradually to about 25° C, and 

 separating the liquid portion from the deposited solid : — 



TABLE II. — Properties of ^Iilk Fat (Rickviond). 



