182 



METHODS OF ANALYSIS. 



ually until it reaches 250 C. The bulb of the tube & should be just outside of 

 the oven, in order that the crystals may form therein. By means of this appa- 

 ratus considerably higher results are obtained than by subliming on a watch 

 glass, as described above. 



PIG. 11. Apparatus for the determination of benzoic acid. 



The sublimate of benzoic acid collected in tube & may be removed by solution 

 in alcohol, and the amount confirmed by titration. A sublimate is sometimes 

 obtained which somewhat resembles benzoic acid in appearance and which has 

 an acid reaction. Before applying the method, therefore, 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 n< 

 sary), as described under salicylic acid. Allow the ether extract to evaporal 

 spontaneously and note the taste of the residue. The presence of saccharin t( 

 the amount of 20 ing per liter is indicated by a sweet taste. This may be con- 

 firmed by henfing with sodium hydroxid, as described below, and detecting tl 

 salicylic acid formed thereby. Results by this method indicating the presem 

 of a. faint trace of saccharin in wines which did not contain it have been fi 

 quently 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 01 

 semisolid, prepared as directed on page 179) and extract with ether. Test tl 

 extracted matter in the usual way for salicylic acid, return the gasoline extrac 

 to the dish containing the residue, dilute the whole to about 10 cc volume, ai 

 add 2 cc of sulphuric acid (1 :3). Bring the solution to the boiling point ai 

 add a 5 per cent solution of potassium permanganate, drop by drop, to slij 

 excess; partly cool the solution, dissolve in it a piece of sodium hydroxid, 

 filter the mixture into a silver dish (silver crucible lids are well adapted to tl 

 purpose) ; evaporate to dryncss and heat for 20 minutes at 210 to 215 C. Dis 

 solve the residue in water, acidify and extract with ether, evaporate the etl 

 and test the residue with two drops of a 2 per cent solution of ferric alum. 

 tliis method all the so-called false saccharin and the salicylic acid naturall 

 present (also added snlicylic aH<l \\lion not present in too large amount) 

 destroyed, while 5 nig of saccharin per liter is detected with certainty. 



