DETEKMINATIONS OF CITRIC ACID. 17 



While still hot the solution is titrated with decinormal alkali, using 

 phenolphthalein as indicator. To the number of cubic centimeters of 

 alkali used must be added 1.5 cc for the potassium bitartrate remain- 

 ing dissolved in the solution. One cubic centimeter of - decinormal 

 alkali equals 0.0150 gram of tartaric acid. 



DETERMINATION OF CITRIC ACID.* 



Fif t}^ cc of the fruit solution are evaporated to sirupy consistency on 

 the water bath. To this residue add 95 per cent alcohol until no further 

 precipitation is formed, pouring very slowly at first and stirring con- 

 stantly. From TO cc to 80 cc are generally sufficient. Filter and 

 wash the residue with alcohol of approximately 95 per cent. Evapo- 

 rate the filtrate to eliminate 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 then drop by drop a saturated solution of lead acetate. The pres- 

 ence of citric acid is shown by the appearance of a precipitate which 

 disappears on heating and reappears on cooling. In order to separate 

 the citric acid from other acids, heat to boiling, filter and wash with 

 boiling water, then allow to cool, and the precipitate of lead citrate 

 will reform. This lead precipitate may be filtered, washed with dilute 

 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 this error can be avoided by adding 

 enough decinormal potash to exactly neutralize the amount of tartaric 

 acid present before adding the alcohol. 



DETERMINATION OF NITROGEN. 



Use 5 grams of jelly or other fruit product or 10 grams of juice or 

 fresh fruit for the determination of nitrogen according to either the 

 Gunning or the Kjeldahl method. Express results as protein (nitro- 

 gen multiplied by 6.25). 



DETERMINATION OF ALCOHOL. 



Transfer 50 grams of the original material to an Erlenmeyer flask 

 of from 250 to 300 cc capacity and increase the volume of the liquid 

 to 150 cc. Attach to a vertical condenser by means of a bent tube and 

 distill 100 cc. Determine the specific gravity of the distillate and cal- 

 culate the percentage of alcohol from a suitable table.'* Unless the 

 specific gravit}^ is taken at 15.6° the temperature correction ma}^ be 

 made according to Table III, Bulletin 59, p. 95. Determinations 

 should be made, however, at as nearly the standard temperature as 

 practicable. 



*M(Jslinger, Ztschr. Unter. Nahr. u. Genus8. 1899, 2, 93. 

 "U. S. Dept. of Agr., Div. of Chem. Bui. 59, p. 65. 



17673— No. 66—02 2 



