CHANGES ON KEEPING. 357 



Vieth has examined a butter which had been kept more than 

 ten years ; the fat then yielded the following Reichert-Wollny 

 figures — 26'2, '2b'6, 25'7, and 21"2 c.c. on difierent portions. 

 He has also examined butter fat which had been kept for eighteen 

 months. 



The results were : — 



Fresh, . . 29-2 c.c. 29-9 c.o. 



Old, . . 30-4 c.c. 29-5 c.c. (determined by the author). 



Another example of butter fat well protected from the light 



N 

 gave in July, 1888, from 31'6 to 32 "1 c.c. of j^ alkali. In — 



October, 1888, it gave 31-8 c.o. 



January, 1889, „ 32-1 „ 



May, 1889, „ 32-1 ,, 



September, 1889, „ 31-8 „ 



December, 1889, „ 32-2 „ 



April, 1890, „ 320 „ 



July, 1893, „ 33 '9 „ 



The last figure was determined by the author ; the others by 

 Vieth. 



It is seen from the figures quoted above that the analysis of 

 butter which has been kept for any length of time is a matter of 

 considerable difficulty. Though in butter fat the volatile acids 

 do not show any diminution, but rather an increase (due pos- 

 sibly tij the oxidation of the glycerol), in butter the reverse is 

 usually the case. It is by no means improbable that, besides 

 the. solubility of these in the water contained in the butter, a 

 portion is destroyed by the action of micro-organisms. The 

 most reliable datum would seem to be the determination of the 

 volatile acids on the butter itself without separation of the fat, 

 subsequent determination of the fat, and calculation of the 

 Reichert figure on the actual fat present. The potash absorption 

 does not appear to undergo much change. 



The phytosteryl acetate test may be applied to rancid butters. 



Detection of Rancidity in Butter. — The amount of free fatty 



N 

 acids in fresh butter does not exceed 5 c.c. — acid per 100 grammes, 



any higher figure indicates partial hydrolysis. Soltsien recom- 

 mends that the fat be steam distilled, treated with alkali in 

 excess, and again steam distiUed. WeUmann's reagent is added 

 to the distillate, and ammonia in excess ; and a blue colouration 

 in from half to one minute indicates rancidity. 



Buttermilk. — Definition. — The term buttermilk is appUed 

 to the aqueous portion left after churning. It differs only 

 slightly in composition from skim milk. As the cream used 



