6 



glass cooled with a piece of ice, or with a condenser the lower end of which is closed with a 

 piece of rubber dam. Or the ether extract (or its solution in gasoline) may be transferred 

 into the tube a, as shown in the accompanying figure, the ether or gasoline removed by a 

 gentle current of air, the tube placed in a vacuum desiccator till its contents are thoroughly 

 dry, and the residue sublimed at the temperature of 250 C., the sublimate being collected 

 in tube 6. During the sublimation, air is drawn very slowly through the apparatus (a wash 

 bottle is used to gauge the speed of the current) to insure the volatilized benzoic acid pass- 

 ing into tube 6. The joint between the two tubes is preferably made by means of a cork 

 stopper. The most satisfactory results are obtained by placing the tube a inside of an oven 



FIG. 1. Apparatus for the determination of benzoic acid. 



the temperature of which is raised gradually until it reaches 250 C. The bulb of the tube 

 5 should be just outside of the oven, in order that the crystals may form therein. By means 

 of this apparatus considerably higher results were obtained than by subliming on a watch 

 glass, as described above. 



The sublimate of benzoic acid collected in tube b may be removed by solution in alcohol, 

 and the amount confirmed by titration. Before applying the method to any class of foods, 

 blank experiments should be made to determine whether a sublimate is obtained under the 

 same conditions from the ether extract of that class of foods. 



3. SACCHARIN, 

 (a) QUALITATIVE DETECTION. 



Extract with ether (after maceration and exhaustion with water if necessary), as described 

 under salicylic acid. Allow the ether extract to evaporate spontaneously and note the 

 taste of the residue. The presence of saccharin to the amount of 20 milligrams per liter 

 is indicated by an intense sweetness. This may be confirmed by heating with sodium 

 hydroxid, as described below, and detecting the salicylic acid formed thereby. Results by 

 this method indicating the presence of a faint trace of saccharin in wines which did not con- 

 tain it have been frequently obtained, owing to the presence in wine of so-called " false 

 saccharin." 



Acidify 50 cc of a liquid food (or the aqueous extract of 50 grams of a solid or semisolid, 

 prepared as directed on page 3) and extract with ether. Test the extracted matter in the 

 usual way for salicylic acid, return the gasoline extract to the dish containing the residue, 

 dilute the whole to about 10 cc volume, and add 2 cc of sulphuric acid (1:3). Bring the solu- 

 tion to the boiling point and add a 5 per cent solution of potassium permanganate, drop by 

 drop, to slight excess; partly cool the solution, dissolve in it a piece of sodium hydroxid, and 

 filter the mixture into a silver dish (silver crucible lids are well adapted to the purpose); 

 evaporate to dryness and heat for twenty minutes at 210 to 215 C. Dissolve the residue 

 in water, acidify and extract with ether, evaporate the ether and test the residue with two 



