69 



mil acids, and other interfering substances. The use of ether is also a source of danger 

 because of its great inflammability. 



Chloroform has always been found inapplicable to the extraction of benzoic acid 

 becuii-e of tin- incompleteness of the extraction so effected. Of the solvents studied, 

 however, it ,-tand- -econd to ether in its power of dissolving benzoic acid. A study 

 wa- therefore made of the efficiency of chloroform in extracting benzoic acid in a sat- 

 urated sodium chlorid .-nlution, and the extraction was found to be practically com- 

 plete. 



In onlrr to determine the efficiency of chloroform with respact to the extraction of 

 interfering -instances, 500 cc of saturated sodium chlorid solution were acidified with 

 5 cc of sulphuric acid (1 to 5), and extracted with four portions of chloroform con- 

 taining 100, 50, 50, and 25 cc, respectively. Each portion of chloroform was removed 

 as completely as possible from the solution, the four portions mixed and distilled on a 

 ht plate toa low volume, the last being removed at ordinary temperature inacurrent 

 of dry air. The residue left by evaporating the chloroform was not weighable. It 

 wa- di. olved in water and titrated with tenth-normal alkali. Duplicate determina- 

 tion- re<|iiire<l 0.03 and 0.04 cc of tenth-normal alkali for neutralization, thus indi- 

 cating that the error, owing to the extraction of mineral acids under the conditions 

 noted, is not greater than iu; mi: "f -odium ben/oate. 



One-half gram of tannin \va- then dissolved in 500 cc of saturated salt solution and 

 ted with chloroform as just described. The residue left by evaporating the 

 chloroform was not wei-hable, but required in the duplicate determinations 0.02 and 

 0.04 cc of tenth-normal alkali for neutrali/.ation, which is equivalent to 0.5 mg of 

 solium ben/oate. < Hie-half gram of tannin and 5 cc of sulphuric acid (1 to 5) were 

 then added to 500 cc of saturated -odium chlorid solution and extracted with chloro- 

 form as described. The re-idue obtained 'by extracting with chloroform was not 

 weighable. duplicate determinations requiring 0.05 and 0.07 cc of alkali, respectively, 

 for their neutrali/ation, equivalent to 0.9 mg of sodium benzoate. 



Tin- presence of acetic arid in the ketchups did not appear to cause any inaccuracy. 

 In order to determine whether a large amount of acetic acid would lead to erroneous 

 re-uli-. I cc of 99.5 per cent acetic acid was dissolved in 200 cc of chloroform and 

 variou- portion-dried, as in the case of the chloroform extract from the samples of ketch- 

 up, and the re-idu. 1. Ten cubic centimeters of the chloroform solution 

 without evaporation require 9 cc of tenth-normal alkali to neutralize it, equiva- 

 lent in <> <>",_> -ram <>t acetic acid, or to o.l 11 gram of sodium benzoate. Ten cubic 

 rentim.-t.-r portion- of the -olution were evaporated before an air blast until no liquid 

 was vi-ible. and HI CC oi \\at.-r were added to the dish and titrated. An alkaline 

 reaction was secured on the addition of O.'J cc of one-hundredth-normal alkali. 

 When Mice jM.rtion- were evaporate* I in the same way and 10 cc of neutral water added 

 to the di-h i) .-_' cc of one-hundredth-normal alkali were required to give an alkaline 

 reaction to phenolphthalein. When 10 cc portions were evaporated until the chloro- 

 form had apparently di-appear -d but a few drops of liquid remained. The odor of 

 ic acid was very apparent and the residue required 0.2 cc of tenth-normal alkali 

 for neutrali/ation. Ten cubic centimeter portions were evaporated until the chloro- 

 form had apparently disappeared, but still contained a slight amount of liquid with a 

 strong odor of acetic acid. The residue was placed overnight in a sulphuric acid 

 desiccator, 10 cc of water were added to the dish and titrated as above, requiring 0.1 

 cc of one-hundredth-normal alkali to give an alkaline reaction. It is apparent that 

 while acetic acid will be extracted by the chloroform, no error is occasioned if care 

 be taken to dry the residue either in a current of air or in a desiccator. It was also 

 found that no appreciable error was caused by the presence of tartaric or citric acid. 

 Lactic acid, when present, was extracted to a considerable extent by chloroform, but 

 after bein- evaporated to dry ness before an air-blast the error amounted to only 0.02 

 per cent. 



