74 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



tion of the oil. In such case wash the "solid residue" from 10 cc of sample with 

 three portions of 5 cc each of ether to remove waxy and fatty matters; dry and weigh 

 residue of cane sugar, deducting 0.38 from the reading for each 0.1 per cent of sugar 

 so found. 



(b) BY PRECIPITATION. 



Pipette 20 cc of the extract into a Babcock milk flask; add 1 cc dilute hydrochloric 

 acid (1:1); add 25 to 28 cc of water previously warmed to 60 C. ; mix and stand in 

 water at 60 for five minutes; whirl in centrifuge for five minutes; fill with warm 

 water to bring the oil into the graduated neck of the flask; repeat whirling for two 

 minutes; stand in water at 60 for a few minutes and read the per cent of oil by . 

 volume. Where the oil of lemon is present in amounts over 2 per cent add to the 

 percentage of oil found 0.4 per cent to correct for the oil retained in solution. Where 

 less than 2 per cent and more than 1 per cent is present, add 0.3 per cent for 

 correction. 



Save the precipitated oil for the determination of refraction. 



When the extract is made in accordance with the United States Pharmacopoeia 

 the results by the two methods just given should agree within 0.2 per cent. 



To obtain per cent by weight from per cent by volume, as found by either of the 

 above methods, multiply the volume percentage by .980 and divide the result by the 

 specific gravity of the original extract. 



8. DETERMINATION OF REFRACTION OF PRECIPITATED OIL. 



(a) Determine the refractive index of the precipitated oil as directed under Edible 

 Oils and Fats on page 22. Compare with similar precipitated oil from standard 

 extract. Or, 



(?>) Place a few drops of the oil obtained above in a Zeiss butyro-refractometer at 

 a temperature of 30. Normal oil when treated under these conditions will have a 

 refraction of 67 to 72 and a dispersion of 2. 



Limonene and most commercial adulterants give a higher reading, with the excep- 

 tion of citronella aldehyde and oil of turpentine. !l 



9. DETECTION OF COLORING MATTERS. 



Follow directions given under coloring materials (p. 111*). For Arata's test (see 

 page 112) the ' ' total residue ' ' may be used after the solution in water. Upon the addi- 

 tion of hydrochloric acid in the determination of oil by precipitation, valuable indi- 

 cations as to the color are frequently given. Tartrazin, napthol yellows, and curcuma 

 retain their color, a pink or red coloration indicates a tropaeolin, while Martius' 

 yellow and salts of di-nitrocresol are precipitated with decolorization of the extract. 



XIII. FRUITS AND FRUIT PRODUCTS. 



By L. S. MUNSON and L. M. TOLMAN, 

 Bureau of Chemistry, U. S. Department of Agriculture. 



1. GENERAL DISCUSSION. 



In the examination of fruits and fruit products, much depends upon the object in 

 view; and the preparation of samples, and the determinations made will depend 

 largely upon the judgment of the analyst. For example, in the determination of 

 heavy metals in canned fruits, one would not be justified in using the liquor, but 

 should work on the pulped contents of the can, while for the detection of glucose, 



Jour. Amor. Chein. Soc., 1899, 21, 1132. 



