MILK FAT. 307 



The following table gives the results of analyses of butter fat 

 and of " margarine" and suet" : 



Good butter. Poor butter. Margarine. Suet. 



Butyric acid ... 5*3 to 6*1 4-6 to 5'1 0*5 0'27 



Caproic acid ... 3-2 to 3-7 2-8 to 3-1 0-3 0-17 



Total volatile acids ... 8*6 to 9'7 7'2 to 8-8 0'8 0-44 



Solid non-volatile acids 82-3 to 82-9 83'8 to 84-6 93'4 91-12 



Blyth and Robertson f have separated butter into a solid 

 crystalline fat and an oil in the proportions of about 45 -5 of 

 butter oil to 54*5 of butter crystals. They ascribe the for- 



fC 4 H 7 o 2 



mula C 3 H 6 -I C lf ,H 31 2 to the solid crystalline body and conclude 



I C ls H 34 2 t 



that butter is mainly made up of compound and not of simple 

 triglycerides. 



All the acids, with the exception of the oleic acid, are 

 saturated compounds of the general formula C n H 2n+1 .COOH. 

 Acids of low molecular weight are liquids soluble in w r ater and 

 volatile in steam ; such are butyric acid, C 3 H 7 COOH, caproic 

 acid, C 5 H n COOH, and caprylic acid, C 7 H 5 COOH, whilst capric 

 and lauric acids are very slightly soluble and volatile. 



The acids of higher molecular weight are solid, insoluble in 

 water, and non-volatile. 



Milk fat, in addition to the above, contains traces of choles- 

 terol, CJHtfOH, lecithin, C 8 H 5 .(C 1H H 35 2 ) 2 .[HP0 4 .N(CH 3 ) 3 C 2 H 4 

 (OH)] (not more than -5% of the fat), and a colouring 

 substance of unknown composition, which has been called 

 . " lac to-chrome." Milk fat is a variable mixture of chemical 

 compounds and therefore liable to considerable variation in 

 properties. Moreover its physical constants, e.g., melting 

 point, are not sharply denned. It is insoluble in water, 

 though capable of dissolving about -g-J n of its weight of water. 

 It is non-volatile at 100, but in contact with air absorbs 

 oxygen and thus increases in weight ; this, no doubt, is 

 because of the unsaturated fatty acids (oleic acid, &c.) present. 

 It melts between 29 '5 and 33 C. (Eichmond) and is therefore 



* Viollette, J.C.S. 1891, abst. 869. t Proc. Chern. Soc. 1889, 5. 



{ So given in the " Proceedings"; probably oleic acid radical, CigH-^O-j, is meant. 



x 2 



