EXAMINATION OF EXTRACTS. 55 



ficial extracts by shaking and observing the color of the resulting foam 

 :i ft er a moment's standing. The foam of pure extract^ is colorless. 

 If caramel is present a color persists at the points of contact between 

 the bubbles until the last bubble has disappeared. The test with 

 fullers' earth given for caramel in vinegar (p. 48) is also very sati- 

 factory, but of course requires the loss of the sample used for the t< -t . 



Examination of the resin. If pure vanilla extract be evaporated to 

 about one-third its volume the resins become insoluble and settle to the 

 bottom of the dish. Artificial extracts remain clear under the same 

 conditions. In examining vanilla extract the character of these resins 

 is studied. For this purpose a dish containing about an ounce of the 

 extract is placed on a teakettle or other vessel of boiling water until 

 the liquid evaporates to about one-third or less of its volume. Owing 

 to the evaporation of the alcohol the resins will then be insoluble. 

 Water may be added to restore the liquid to approximate!}^ its original 

 volume. The resin will then separate out as a brown nocculent pre'- 

 cipitate. A few drops of hydrochloric acid may be added and the 

 liquid stirred and the insoluble matter allowed to settle. It is then 

 filtered and the resin on the filter paper washed with water. The resin 

 is then dissolved in a little alcohol, and to one portion of this solution 

 is added a small particle of ferric alum and to another portion a few 

 drops of hydrochloric acid. If the resin be that of the vanilla bean, 

 neither ferric alum nor hydrochloric acid will produce more than 

 a slight change of color. With resins from most other sources, how- 

 ever, one or both of these substances yield a distinct color change. 



For filtering, a piece of filter paper should be folded once through 

 the middle, and again at right angles to the first fold. It may now be 

 opened with one fold on one side and three on the other and fitted into 

 a glass funnel. When the paper is folded in this manner the precipi- 

 tated resins may be readily washed with water. When the washing is 

 completed the resins may be dissolved by pouring alcohol through the 

 filter. This work with the resins will require some practice before it 

 can be successfully performed. It is of considerable value, however, 



judging of the purity of vanilla extract. 



LEMON EXTRACT. 



By lemon extract is understood a solution of lemon oil in strong 

 ilcohol. In order to contain as much lemon oil as is supposed to be 

 found in high-grade extracts the alcohol should constitute about 80 

 per cent of the sample. The alcohol is therefore the most valuable 

 constituent of lemon extract, and manufacturers who turn out a 

 low-grade product usually do so because of their economy of alcohol 

 rather than of lemon oil. Owing to the fact that lemon extract is 

 practically a saturated solution of oil of lemon in strong alcohol the 

 sample may be examined by simple dilution with water. A teaspoon- 



