56 ANALYSIS AND ADULTERATIONS OF BUTTER. 



Beaker, filter, and fatty acids (2 hours) ... 24-4642 



(2J ) ... 24-4500 



(3 ) ... 244505 



Fatty acids 2-8703 



Fatty acids, 87 -42 per cent. 



It is to "be borne in mind that the fat acids are compara- 

 tively unstable compounds, not as unalterable by keeping or 

 exposure to the air as are the majority of the substances 

 obtained in mineral analysis. It cannot, therefore, be won- 

 dered at, that the weight of these acids does not keep abso- 

 lutely constant on heating to the boiling point of water, but 

 that it varies to some extent, according to the time they are 

 exposed in a fused state to the action of oxygen. This 

 change, however, takes place very gradually, and does not by 

 any means prevent accurate determination, as will be seen 

 from the following figures : 



Beaker and fatty acids after 2 hours' drying ... 24*4642 



2J C ... 24-4500 



3 ... 24-4505 



3J ... 24-4504 



4J ... 24-4504 



6 ... 24-4517 



7 ... 24-4556 

 11 ,.. 24-4553 

 17 ... 24-4526 



After 7 hours' drying at 100 C., the fatty acids kept de- 

 creasing slowly, and after 22 hours they again weighed as 

 much as after 2 J hours. After two days the decrease became 

 much more marked, the fatty acids turning deep brown, and 

 emitting a highly rancid odour. It will be noticed that there 

 is no difficulty in obtaining the correct weight, as the changes 

 are but very gradual and slow. The increase which first 



