94S Journal of Agricultural Research vol. vi, No. 24 



mum, from which point it begins to decrease. It is also very clear from 

 the control experiment given in Table XIX that the change in the com- 

 position of the air inclosed in the material is not caused by decomposi- 

 tion of the lactic acid itself or to any action of this acid upon the par- 

 ticles of pumice. 



It has already been shown in this paper that the acidity of the cream 

 from which the butter is made has a direct influence on the change, 

 during storage at a temperature of o° F., in the composition of the air 

 incorporated into the butter at the time of its manufacture. It has 

 also been shown that but a slight change is to be observed in the com- 

 position of the air from a tube containing a small quantity of pure butter 

 fat exposed to the action of a large and confined surface of air while 

 the fat was kept at a temperature of 32 ° F. It has likewise been demon- 

 strated that practically no change in the composition of the air occurs 

 when pure butter fat is exposed to the action of about the same amount 

 of air as is usually present in normal butter while it is stored at a tem- 

 perature of o° F. As it has been proved by an analysis of the air from 

 a sample of sweet-cream butter made from cream of low acidity that 

 this kind of butter suffers very little, if any, measurable decomposition 

 during a period of six months in storage at a temperature of o° F., and 

 having also proved by other experiments that a decomposition of the 

 fat of whole butter stored at a temperature of o° F. for the same length 

 of time is practically excluded, it is a logical conclusion that the particles 

 of buttermilk inclosed in a sample of sweet-cream butter made from 

 cream of low acidity likewise suffers little, if any, measurable decompo- 

 sition when the butter is stored at a temperature of o° F. It was de- 

 cided, however, to settle this point definitely by experiment. 



For this purpose the pumice of a third lot of tubes was impregnated 

 with buttermilk from sweet-cream butter made from pasteurized cream 

 having an acidity of 0.108 per cent (calculated as lactic acid). The 

 acidity of the cream in this case was practically the same as that of the 

 cream from which the foregoing sample of sweet-cream butter was made. 

 This last lot of tubes containing the sweet-cream buttermilk was kept 

 at a temperature of o° F. (Table XX). 



Table XX. — Oxidation of sweet-cream buttermilk exposed to the action of a large surface 



of air at 0° F. 



Period at o° F. 



Days. 



35 



65 



270 



Oxygen. 



Per cent. 

 20. 92 

 20.93 

 20. 25 



Carbon dioxid. 



Per cent. 



That the sweet-cream buttermilk underwent practically no change in 

 storage at a temperature of o° F. is shown by the foregoing data. 



