80 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



this calculate the citric acid. Again evaporate the filtrate to about 20 cc and add 3 

 volumes of 96 per cent alcohol by volume, which will throw down the calcium salt 

 of tartaric acid held in solution, the rest of the citrate, and the malateand succinate. 

 Filter this off, ignite, titrate,, and calculate as malic acid, after subtracting the tartaric 

 acid present, as the amount of citric and succinic acid present is very small. 



18. DETERMINATION OP TARTARIC ACID. a 



To 100 cc of the fruit juice add 2 cc of glacial acetic acid, 2 or 3 drops of a 20 per 

 cent potassium acetate solution and 15 grams of pure finely powdered potassium chlo- 

 rid, dissolve this by shaking, and then add 20 cc of 96 per cent alcohol. Then stir 

 vigorously for one minute, rubbing the walls of the beaker with the glass stirring rod 

 to start the crystallization of the potassium bitartrate. Allow to stand 15 hours at 

 room temperature. Filter and wash the precipitate onto a Gooch crucible with a 

 thin asbestos felt, using the vacuum pump. Wash with a mixture of 15 grams of 

 potassium chlorid, 20 cc alcohol, and 100 cc water. The beaker is rinsed three 

 times with a few cubic centimeters of this solution. The precipitate is also washed 

 with a few cubic centimeters, but so that not more than 20 cc in all of the wash solu- 

 tion is used. The precipitate and asbestos filter are washed back into the beaker 

 and heated to boiling. While still hot the solution is titrated with decinormal 

 alkali, using phenolphthalein as indicator. To the amount of alkali used must be 

 added 15 cc for the potassium bitartrate remaining dissolved in the solution. One 

 cubic centimeter of decinormal alkali is equivalent to .0150 grams potassium bitartrate. 



19. DETERMINATION OF CITRIC Acm. b 



Fifty cubic centimeters of the fruit solution is evaporated on the water bath to a 

 sirupy condition. To the residue add, very slowly at first, stirring constantly, 95 per 

 cent alcohol until no further precipitate is formed; 70 to 80 cc are generally enough. 

 Filter and wash the residue with 95 per cent alcohol. Evaporate the filtrate to elim- 

 inate the alcohol, take up the residue with a little water and transfer to a graduated 

 cylinder, making up to 10 cc. To 5 cc of this solution add half a cubic centimeter of 

 glacial acetic acid, and to this add, drop by drop, a saturated solution of lead acetate. 

 The presence of citric acid is shown by the appearance of a precipitate which pos- 

 sesses the property of disappearing on being heated and reappearing on cooling. In 

 order to separate the citric acicl from other acids, heat to boiling, filter, and wash 

 with boiling water; then allow to cool and the precipitate of lead citrate will re-form. 

 This lead precipitate may be filtered off, washed into weak alcohol, dried, weighed, 

 and the citric acid calculated. It is necessary that there shall be no tartaric acid 

 present. If the tartaric acid has been estimated, any error on this account may be 

 avoided by adding enough decinormal potash to neutralize the tartaric acid before the 

 alcohol is added. 



20. DETECTION OF PRESERVATIVES. 



Dissolve about 25 grams of the sample in water, acidify, and extract with ether. 

 Remove the ether layer and allow it to evaporate spontaneously. Take up the residue, 

 which may contain salicylic and benzpic acids and saccharin, with water. For 

 detecting preservatives so senarated, and to test further for preservatives, use methods 

 described by the referee on that subject (p. 107). 



21. DETECTION OF COLORING MATTER. 

 Follow directions given on pages 111 and following. 



22. DETECTION OF ARTIFICIAL SWEETENING MATERIALS. 

 Follow directions given on page 89. 



Halenke & Moslingcr, Ztschr. anal. Chem., 1895, 34, 283. 

 bMoslinger, Ztschr. Untcr. Nahr. u. Genuss., 1899, 2: 93. 



