12 THE FAT OF MILK. 



In the first stage, sodium ethoxide and fat form sodium glycer- 

 oxide and ethyl salts (esters). 



In the second, the glyceroxide is decomposed by the water 

 present into glycerol and sodium hydroxide ; while, in the third, 

 the esters are hydrolysed by the hydroxide into alcohol and 

 sodium salts of the fatty acids (soaps). 



The action between the sodium hydroxide and the alcohol is 

 never complete, and it is probable that the formation of esters 

 is only partial ; evidence of the formation of ethyl butyrate can 

 be obtained by warming a little of the fat with alcoholic soda, 

 when the characteristic pine-apple odour of ethyl butyrate is at 

 once developed. By carefully avoiding any excess of alkali and 

 distilling the ethyl butyrate as soon as possible, Wanklyn and 

 Fox have succeeded in obtaining about 3 per cent, of volatile 

 acid (probably chiefly butyric) in the form of ester. 



It is probable that the equation (ii.) may not represent the 

 way in which sodium glyceroxide acts on the substances present ; 

 a portion may follow this equation 



(iv. ) C 3 H 5 (ONa) 3 + 3C. 2 H 5 OH = C 3 H 5 (OH) 3 + 3C 2 H 5 ONa. 



The glyceroxide may act on alcohol forming ethoxide, instead 

 of on water forming hydroxide. 



Allen and Homfrey 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 in 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 be 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. Milk 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 hydrogen, 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. 



