74 MILK PRODUCTS. 



melted fat is of value in this connection, but the dis- 

 tinction between butter and its substitutes is not so 

 sharp as with the distillation method. The same re- 

 mark applies to the iodin absorption figure and to the 

 refractive index. The latter can be accurately meas- 

 ured by means of an instrument called the oleo-refrac- 

 tometer. 



Considerable use has been made of a method based 

 upon the detection of crystalline structure by examin- 

 ation with polarized light. Such condition indicates 

 however, merely that the sample has been previously 

 melted. By churning oleo-oil with cream, a material 

 is obtained which shows no crystalline structure when 

 examined in this way. 



Commercial forms of oleomargarin and butter exhibit 

 characteristic differences on heating, which may be 

 utilized for rapidly sorting a collection of samples. 

 When butter is heated in a small tin dish directly 

 over a gas flame, it melts quietly, foams and may run 

 over the dish. Oleomargarin, under the same condi- 

 tions, sputters noisily as soon as heated and foams but 

 little. Even mixtures of butter and other fats show 

 this sputtering action to a considerable extent. The 

 effect depends upon the condition in which the ad- 

 mixed water exists, and the test is not applicable to 

 butter which has been melted and reworked. 



An alcoholic solution of sodium hydroxid heated 

 for a moment with butter and then emptied into cold 

 water, gives a distinct odor of pineapples (due to ethyl 



