56 FOOD ADULTERATION AND METHODS FOB DETECTION. 



ful of the oil in question may be placed in the bottom of an ordinary 

 glass tumbler and 2 or 3 teaspoonfuls of water added. If the sample 

 in question be real lemon extract the lemon oil should be thrown out 

 of solution by reason of its insolubility in the alcohol after its dilution 

 with water. The result is at first a marked turbidity and later the 

 separation of the oil of lemon on the top of the aqueous liquid. If the 

 sample remains perfectly clear after the addition of water, or if a 

 marked turbidity is not produced, it is a low-grade product and con- 

 tains very little, if any, oil of lemon. 



FRUIT PRODUCTS. 



Adulteration of fruit products is practically confined to jellies and 

 jams. Contrary to the general belief, gelatin is never used in making 

 fruit jelly. In the manufacture of the very cheapest grade of jellies 

 starch is sometimes employed. Jellies containing starch, however, 

 are so crude in their appearance that the most superficial inspection is 

 sufficient to demonstrate that they are not pure fruit jellies. From 

 their appearance no one would think it worth while to examine them 

 to determine their purity. 



Natural fruit jellies become liquid on being warmed. A spoonful 

 dissolves readily in warm water, although considerable time is required 

 with those that are especially firm. The small fruits contain practi- 

 cally no starch, as apples do, and the presence of starch in a jelly 

 indicates that some apple juice has probably been used in its prepara- 

 tion. (As stated above, jelly that has been thickened by starch paste 

 will not be mistaken for fruit jelly.) 



DETECTION OF STARCH. 



Dissolve a teaspoonf ul of jelly in a half teacupful of hot water, heat 

 to boiling and add, drop by drop, while stirring with a teaspoon, a 

 solution of potassium permanganate until the solution is almost color- 

 less. Then allow the solution to .-ool and test for starch with tincture 

 of iodin, as directed on page 58. Artificially colored jellies are some- 

 times not decolorized by potassium permanganate. Even without 

 decolorizing, however, the blue color can usually be seen. 



DETECTION OP GLUCOSE. 



For the detection of glucose, a teaspoonful of the jelly may h< dis- 

 solved in a glass tumbler or bottle in '2 or 3 tablospoonfuls of water. 

 The vessel in which the jelly is dissolved may be placed in hot water 

 if necessary to hasten the solution. In case a jam or marmalade is 

 being examined, the mixture is filtered to separate the insoluble mat- 

 ter. The solution is allowed to cool, and an equal volume or a little 

 more of strong alcohol is added. If tin- sample is a pure fruit product 

 the addition of alcohol causes no precipitation, except that a very 



