20 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



II. EDIBLE OILS AND FATS. 



By L. M. TOLMAN, 

 Bureau of Chemistry, United States Department of Agriculture. 



1. GENERAL DISCUSSION. 



In working with oils and fats the same methods of examination largely apply, 

 except in preparation of the sample. 



The solid fats should first be melted, thoroughly mixed, and then filtered by means 

 of a hot- water funnel or similar apparatus. Samples for the different determinations 

 are taken from this melted homogeneous mass. The specific gravity must be taken 

 at some temperature above the melting point of the fat. The boiling point of water 

 has been largely used, and, although there are inherent errors in such a method, a 

 it probably gives the most satisfactory results for practical work. 



In the Maumene test, fats require a higher initial temperature than oils. 



With oils in most cases the sample for analysis requires no preliminary treatment, 

 except that in case of impurities the oil should be filtered. 



Oil and fat should always be kept in a cool place, otherwise they will soon become 

 rancid, which will affect more or less the physical and chemical constants. b The iodin 

 number decreases with rancidity, while specific gravity, index of refraction, and 

 acetyl value increase. Too much confidence must not be placed in negative results 

 obtained in a single determination, but only upon making a complete quantitative as 

 well as qualitative examination can a reliable judgment of purity be made. 



Oils and fats being variable mixtures of glycerids of the fatty acids, their phys- 

 ical and chemical constants vary within limits fairly well established from analytical 

 data. However, too much dependence must not be placed upon the more common 

 determinations, as it is easy to make such mixtures of either fats or oils as will satisfy 

 the ordinary requirements as to specific gravity, index of refraction, heat with sul- 

 phuric acid, iodin absorption, and saponification value. 



The melting point of the fats and the fatty acids is difficult to determine, because 

 they are mixtures of glycerids or acids, substances which have widely varying melt- 

 ing points. A wide difference has resulted from the varied usage of different analysts, 

 and results obtained by exactly the same method are the only ones that are strictly 

 comparable. For fats Wiley's method of determining melting point has been adopted 

 by the Association of Official Agricultural Chemists. 



For the free fatty acids obviously this will not do, and the capillary tube was 

 chosen as being a method most generally used and giving the most satisfactory 

 results. 



2. DETERMINATION OF SPECIFIC GRAVITY. c 



(a) DETERMINATION AT 15.5 0. 



Determine the specific gravity of oils at 15.5 C. by the use of a pycnometer, West- 

 phal balance, d or accurately graduated hydrometer. e 



If determined at room temperature, the following formula may be used to calcu- 

 late the specific gravity at 15.5 C. : f 



G=G / +-00064 (T-15.5 C.). 



G=sp. gr. at 15.5. 



G'=sp. gr. at T. 



0.00064= mean correction for 1 C. 



E. E. Ewell, U. S. Dept. Agr., Div. Chem., Bui. 62, p. 125. 



E.Spaeth, Ztschr. anal. Chem., 1896, 35, 471-493; C. A. Browne, Jour. Am. Chem.Soc., 1899,21, 989-994. 

 c See appendix, p. 149. 



d C. A. Crampton, U. S. Dept. of Agr., Div. of Chem., Bui. 13, pt. 4, p. 438. 



Accurately made hydrometers reading from sp. gr. 0.900 to 0.940 at 15.5 C. will satisfy every require- 

 ment of accuracy and speed. 



'Allen, Com. Org. Anal., 3d ed., vol. 2, pt. 1, p. 33: Winton, Conn. Expt. Sta. Kept., pt, 2, 1900, p. 149. 



