76 



higher than those given by titration, whereas the amounts determined by precipita- 

 tion as silver benzoate are almost identical with the amount obtained by titrating 

 the chloroform residue. This method is evidently worthy of further study. It is 

 much more tedious than Method II, but is of value for the purpose of checking the 

 results obtained by that method when a further confirmation seems desirable. 



Determination of betizoic acid in commercial samples of tomato hichup by precipitation 

 as silver salt from chloroform extract. 



These samples were treated according to Method II, given on page 70. The residue 

 obtained by the evaporation of the chloroform extract was first weighed, then dissolved 

 in about 5 cc of neutral alcohol, the solution so obtained diluted with water and 

 titrated with saturated alkali solution. This solution when exactly neutralized is 

 evaporated to dryness, after which the benzoic acid was determined by precipitation 

 as silver benzoate. 



THE DISTILLATION OF BENZOIC ACID FROM SULPHURIC ACID SOLUTION (METHOD V). 



This method was suggested and elaborated by Mr. R. M. West," and depends on 

 the distillation of benzoic acid with steam after the addition of sufficient concentrated 

 sulphuric acid to insure the complete charring of vegetable tissue and prevent vola- 

 tilization of coloring matter and oil. The distillation is conducted by means of a flask 

 shown on page 21, the procedure being as follows: 



About 10 grams of the sample are weighed into the inner flask of the apparatus, 

 1.5 to 2 grams of paraffin added, and the flask connected with the condenser. Ten 

 cubic centimeters of strong sulphuric acid are added through a drop funnel at a rate 

 sufficient to complete the addition at from two to three minutes, the flask is gently 

 agitated, to mix the contents thoroughly, and allowed to stand from five to ten minutes 

 after all apparent action of the sulphuric acid has ceased. About 150 cc of distilled 

 water are placed in the outer flask of the apparatus and the water slowly brought to a 

 boil and the boiling continued until 100 cc of the distillate have been collected. 

 The stopcock in the outer flask is left open until the water has heated sufficiently to 

 prevent the contents of the inner flask being drawn into the outer flask. 



The distillate is filtered into a separatory funnel and the original receiver and filter 

 are washed with two portions of water of about 10 cc each. The distillate is then 

 extracted with three portions of ether of 50, 30, and 20 cc, respectively. The com- 

 bined ether extracts are washed repeatedly with water until a 25 cc portion requires 

 not more than 0.10 cc of decinormal alkali for neutralization. The ether extract is 

 then distilled to small volume, after which it is evaporated before a blast of air, dried 

 in a desiccator to constant weight and weighed. The residue is also dissolved in 

 neutral alkali, using phenolphthalein as indicator. 



The results obtained by titration agree closely with those obtained by weighing. 

 Excessive foaming is likely to occur when the steam begins to pass into the inner 

 flask. This may be caused by distilling too soon after the addition of the acid, by an 

 insufficient amount of paraffin, or by an unusual amount of sugar in the ketchup. 

 Care must be exercised to prevent the foam passing into the condenser. 



J. Ind. and Eng. Chem., 1909, 1: 190. 



