72 



An approximate determination of the solubility of benzoic acid in a saturated solu- 

 tion of sodium chlorid was made by P. B. Dunbar. In duplicate tests 0.260 and 

 0.259 gram of benzoic acid were dissolved in 500 cc of saturated solution of sodium 

 chlorid. In another duplicate determination 0.274 and 0.277 gram of benzoic acid 

 were found to be soluble in 500 grams of saturated solution of sodium chlorid to which 

 5 grams of sulphuric acid (1 to 5) had been added. No special precautions were taken 

 with respect to the temperature of solutions or the purity of the sodium chlorid 

 employed. 



It is apparent therefore that a larger amount of benzoate of soda than 0.27 gram 

 can probably not be determined by this method. The fact that a slightly higher 

 amount is reported in some determinations may probably be explained by slightly 

 higher temperature, or slightly lower concentration of the sodium chlorid solution 

 employed. 



It is obviously important that the method be so modified as to permit the deter- 

 mination of a larger amount of benzoate of soda. Attempts were made to extract 

 the benzoic acid from the ketchup by means of water, filtering, and saturating an 

 aliquot part of the filtrate with sodium chlorid. The results obtained were not alto- 

 gether satisfactory, although the amount of work done was not sufficient to permit of 

 definite conclusions. It is probable that by extracting in this manner or with a satu- 

 rated sodium chlorid solution, previously made slightly alkaline with sodium hy- 

 droxid, the method can be so modified as to permit of its application to samples 

 carrying a much higher percentage of benzoate of soda, and at the same time it will 

 be possible to extract a smaller volume of the salt solution. 



PRECIPITATION WITH COPPER BENZOATE (METHOD III). 



Mr. C. S. Ash, of the California Wine Association, and Mr. F. W. Liepsner, of the 

 Division of Foods of the Bureau of Chemistry, studied the determination of benzoic 

 acid by means of precipitation as copper benzoate from the residue left by the evapo- 

 ration of the solvent. It was hoped that this method might afford a means for deter- 

 mining benzoic acid either alone or in the presence of salicylic acid, but preliminary 

 work showed that while copper acetate is a satisfactory precipitant for benzoic acid 

 when present alone, no precipitate is formed in the presence of salicylic acid in con- 

 siderable quantity, owing probably to the formation of a soluble double salt. 



A series of precipitations of benzoic acid were made in alcoholic solutions of various 

 strengths from to 100 per cent and the curve established, giving the per cent of 

 benzoic acid present that may be precipitated as copper benzoate in various strengths 

 of alcohol. The results are as follows: 



Precipitation of benzoic acid with varying strengths of alcohol. 



It appears that the amount of benzoic acid precipitated is somewhat increased by 

 the presence of alcohol up to 20 per cent of the latter. The increase in strength of 

 the alcohol beyond this point decreases the amount of benzoic acid precipitated, at 

 first slowly and then rapidly, the copper benzoate being completely soluble in strong 

 alcohol. All precipitations were therefore made in a solution containing 20 per cent 

 of alcohol by volume. 



