42 



INTRODUCTORY — THE CONSTITUENTS OF MILK. 



The fat consists of a mixture of glycerides — i.e., ethereal salts 

 of glycerol. It appears most probable that there are three acid 

 radicles in combination with each glycerol residue, thus — 



C,H-, 



C4HTO2 

 C,„H,,02 



which represents glyceryl butyro-oleo-stearate. This view has 

 been formed from the following facts : — (1) Were the fat a 

 mixture of glyceryl tributyrate with other glycerides, it would 

 be possible to dissolve out the glyceryl tributyrate by means of 

 alcohol, leaving nearly the whole of the other glycerides behind. 

 This is not the case. The portion soluble in alcohol contains 

 a notable quantity of the higher glycerides. 



(2) If glyceryl tributyrate existed as such in milk fat it should 

 be possible to distil it off under reduced pressure, but this cannot 

 he done. 



We know nothing of the way in which the fatty acids are 

 combined with glycerol ; it is convenient, however, to state the 

 composition as if each glyceride existed separately. 



Composition. — The average composition of the fat of milk 

 appears to be, from the mean results obtained by different 

 observers, as follows : — 



Biitj'rin, 

 Caproin, 

 Caprylin, 

 Caprin, 

 Laurin, 

 Myristin, 20-2 

 Palmitin, 25-7 

 Stearin, 1 '8 

 01eiii,&c., .35-0 



3'85 percent, j'ielding 3 



3-60 



0-55 



1-9 



7-4 



3 

 

 1 

 6 



19 



•2i 



I 



33 



43 % Fattj' acids and 1 



25 



51 



1' 



Total, 100-00 



Insoluble, 87 '65 

 Total, 94-84 



94 

 14 



48 

 72 

 60 



17 % Glycerol. 



86 



10 



31 



07 



53 



91 



19 



39 



Total, 12-53 



C. A. Browne states that TO per cent, of dioxystearic acid 

 occurs in butter, and 0-1 per cent, of unsaponifiable matter. 



In this table, butyric, caproic, and caprylic acids have been 

 classed as soluble in water, and the others insoluble ; this is not, 

 strictly speaking, correct, as capric and, probably, lauric acids 

 are also slightly soluble ; on the other hand, caprylic acid pos- 

 sesses so slight a solubility in water that it probably is not wholly 

 dissolved. 



The figure 87-65 per cent, is, however, a near approximation 

 to the mean found for the insoluble fatty acids. The figure 

 for the total amount of glycerol 12-53 also agrees with that 

 found. 



