FAT CRYSTALS I 01 



brown zone which deepens to wine red. The reaction for sperm 

 oil is much as for cod-hver oil. These color reactions with sul- 

 phuric acid are perhaps of little value in the detection of fat adul- 

 terations and admixtures but they will prove helpful aids in the 

 examination of these substances as to identity. Pure concen- 

 trated acid should be used. It must also be kept in mind that the 

 fat impurities which may be present modify the color reactions. 

 Pure samples of fats should be kept on hand for purposes of making 

 check and comparative tests. The Bureau of Animal Industry 

 has suggested a method for distinguishing between fats and oils 

 derived from the animal and the vegetable kingdoms based upon 

 differences in the appearance of the crystals (phytosterol and 

 cholesterol) . 



In addition to the study of fat crystals which are formed spon- 

 taneously in more or less decomposed and aged meat products as 

 above set forth, certain methods for testing fat crystals isolated 

 in the pure state by chemical methods are now generally carried 

 out in meat inspection and food laboratories. These tests com- 

 bine the use of the compound microscope and should therefore 

 be carried out by the micro-analyst or bacteriologist and for that 

 reason are hereby included. R. H. Kerr of the Biochemic Divi- 

 sion of the Bureau of Animal Industry has worked out a method 

 for detecting vegetable fats in mixtures of animal and vegetable 

 fats and vice versa, the method will also serve to demonstrate the 

 presence of animal fats in supposedly pure vegetable fats. The 

 method is a slight modification of several methods which have been 

 in use for some time and which are described in various text-books, 

 and it is hereby given in full as it appears in Circular No. 212 (May 

 10, 1913) of the Bureau of Animal Industry. 



The Detection of Phytosterol in Mixtures of Animal and 



Vegetable Fats 



Sample. — The amount of sample used depends on the amount of material avail- 

 able. From 200 to 300 grams is the amount usually taken. The test is seldom 



