then extract color from fuller's earth with hot alcohol, and apply 

 tests for identifying the color. 



(3) Shake gasoline solution of colored oil or fat with very weak 

 potassium hyclroxid solution (Leed's method). 



(4) Shake the oil or melted fat with boiling 90 per cent alcohol for 

 several minutes. Cool with ice about one hour, then filter through a 



' O 



filter wet with alcohol. Reduce the volume of the alcohol solution 

 about one-third on the water bath and decant or filter from any oil 

 which separates on cooling. The color may be separated from this 

 oil by the method under (1). Color tests may now be applied to the 

 alcoholic solution of the color or to the dry color obtained by its 

 evaporation. This alcoholic solution would, of course, also contain 

 any free fatty acids, cholesterol, or phytosterol in the oil or fat. 



DETECTION OF MIXED COLORS. 



(1) Macroscopic or microscopic examination of dry color. 



(2) One of the best ways for testing mechanically mixed, dry 

 colors is by sprinkling the powdered color on the surface of sulphuric 

 acid in a broad shallow dish, such as a petri culture dish, and noticing 

 any difference in the colored spots formed. A similar method with 

 water is commonly used, and it is recommended that this test be 

 carried out as follows: 



Fill a 500 cc Griffin beaker to the depth of about 4 inches with 

 water, or in some cases preferably with dilute alcohol. On the sur- 

 face sprinkle the powdered color. The streaks of color formed in the 

 liquid as the particles fall to the bottom of the beaker will generally 

 indicate plainly whether one or more colors are present. 



(3) Capillarity test. (Allen, Commercial Organic Analysis, vol. 3, 

 pt. 1, p. 478.) 



(4) Fractional dyeing. (Allen, loc. cit., p. 479.) 



(5) Treatment of dry color with various solvents, or extraction of 

 aqueous solution with immiscible. solvents, and making comparative 

 dyeing tests with extracted color and residual color in aqueous 

 solution. 



NATURAL COLORING MATTERS. 



It is generally very difficult to isolate natural coloring matters in a 

 state of purity, and the task of identifying them with certainty is 

 still more complicated. They can best be separated by extraction 

 with an immiscible solvent, or by dyeing on wool, mordanted with 

 alum, tin, or chromium. Special tests have also been devised for 

 the more common natural coloring matters, which can be found in 

 any standard work on food analysis. Caramel is extensively used 

 as a coloring matter in food products, and its detection is important, 

 especially in vanilla extracts and liquors. In case of a brown-colored 



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