60 COMPOSITION OF AMERICAN WINES. 



2 to 3 cc of strong sulphuric acid and heated until white fumes appear. 

 By this means benzoic acid is converted into sulphobenzoic acid. A 

 few crystals of potassium nitrate are added and the heating continued 

 until the solution is almost or quite colorless. This causes the forma- 

 tion of metadinitrobenzoic acid. When cool the acid is poured into 

 water and ammonia added in excess, followed by a drop or two of 

 ammonium sulphid. The nitro compound becomes converted into 

 ammonium metadiamidobenzoate, which possesses a peculiar reddish- 

 brown color. This reaction takes place immediately and is seen at the 

 surface of the liquid without stirring. Salicylic acid will sometimes 

 give the same reaction, but only after waiting some minutes. The 

 benzoic acid must first be separated in a state of .approximate purity 

 before this test can be applied. Half a milligram of the acid can be 

 detected in the absence of interfering bodies. This reaction is also 

 given b}^ saccharin. 



Pet^s method. 1 For this method the wine is extracted by shaking 

 with chloroform in a separately funnel after acidifying with 5 cc of 

 1-3 sulphuric acid. The chloroform is allowed to evaporate to dryness 

 in a small porcelain dish. When benzoic acid is present in consider- 

 able quantities the crystalline character of the residue f requently indi- 

 cates its presence. The dish containing the residue is placed in a ves 

 sel of ice water, a few cubic centimeters of strong sulphuric acid are 

 added, and the contents are then stirred until the residue is dissolved. 

 Barium peroxid is then gradually dusted into the dish, with continual 

 stirring, until the liquid begins to foam, after which a few cubic centi- 

 meters of commercial hydrogen peroxid are added drop by drop. The 

 dish is then taken from the water, and its contents are diluted with 

 water to convenient bulk, the barium sulphate is removed by filtration, 

 and the filtrate, which should still be acid, shaken with chloroform. 

 The chloroform extract is then tested for salicylic acid as directed in the 

 method for the detection of salicylic acid. Dr. Peter also suggests 

 that persulphate of ammonium affects this oxidization. 



The presence of benzoic acid may be confirmed by neutralizing the 

 aqueous solution of the extracted benzoic acid with sodium hydroxid, 

 evaporating to a very small volume, and acidifying with sulphuric 

 acid, when the presence of a large amount of benzoic acid is indicated 

 by the formation of a white flocculent precipitate. The concentrated 

 solution of the sodium salt may be further tested by making it exactly 

 neutral and adding a drop of a dilute ferric chlorid solution, when 

 ferric benzoate is precipitated in the presence of a large amount of 

 benzoic acid. The appearance of ferric benzoate is markedly different 

 from that of ferric hydroxid, in that it is almost white when viewed 

 by transmitted light, whereas ferric hydroxid has a brown color under 

 the same conditions. 



1 Unpublished. Inserted here by courtesy of the author, Dr. A. M. Peter. 



