II 



BUTTER 



I S9 



impossible to distinguish one from the other without a chemical 

 or physical examination. The chemical difference consists 

 naturally in the absence of volatile fatty acids, except the 

 unimportant quantity which comes from the churning with 

 milk or cream. 



1. Determination of the Refractive Index of the Fat. 



The figures which Wollny gives as limits between which the 

 refractive index of natural butter varies are, as has previously 

 been mentioned, 49'5-54'0 divisions of the butter refractometer 

 at 25 C., and 40'5-44'4 at 40 C. Later investigations have, 

 however, shown that these limits are too narrow, for the 

 refractive index can sometimes rise to 47 divisions at 40 C. 

 Such exceptionally high refractive indices are usually found in 

 connection with very low Reichert-Meissl numbers. The limits 

 in the case of margarine fat are 58'6-66'4 at 25 C., and 

 48-52 at 40 C. An addition of margarine to butter may 

 therefore be detected by a raising of the normal refractometer 

 figure, provided that the adulteration is not so small that the 

 refractive index of the mixture falls within the boundary of 

 that for pure butter fat. If the number shown on the 

 refractometer exceeds the maximum for butter, then the 

 sample must be regarded as very suspicious. An examina- 

 tion with the refractometer cannot, however, be taken as a 

 sufficient proof of falsification, but rather as an indication that 

 a chemical examination ought to be made. 



In the following are shown the maximum number of scale 

 divisions between 45 and 25 C. that are permissible for 

 pure butter. 



Highest Allowable Refractometer Readings for Pure Butter at 

 Different Temperatures. 



