DETECTION OF PRESERVATIVES. 59 



than is the case with the other preservatives, because a small amount 

 of boric acid is normal to wines. It is sometimes a difficult matter 

 to fix the amount which may naturally occur. In order to make this 

 test of practical value, therefore, it is essential that the determination 

 of boric acid should be quantitative. The alkaline fluorides, as well 

 as the alkaline borofluorides and silicofluorides, are coming into some- 



o 



what more general use now as food preservatives, although they have 

 not been frequently reported in wines. 



DETECTION OF SALICYLIC ACID. 



About 75 cc of the sample are acidified with 5 cc of dilute (1-3) sul- 

 phuric acid, and extracted in a separately funnel with ether or chloro- 

 form. If the former solvent be employed the ether is transferred to a 

 porcelain dish and allowed to evaporate spontaneously, and the residue 

 is digested for a short time with a few cubic centimeters of gasoline, 

 which has a boiling point below 60. The gasoline is then transferred 

 to another evaporating dish, and allowed to evaporate spontaneously. 

 The residue is dissolved in 1 to 2 cc of water and tested with a 0.5 per 

 cent solution of ferric chlorid. The presence of salicylic acid is indi- 

 cated by the formation of a marked violet color, which is soluble in 

 water. In case of any turbidity which masks the color, filtration may 

 be resorted to and the color of the filtrate noted. When chloroform 

 is used as the solvent the test may be made directly in the chloroform 

 solution with ferric chlorid. 



DETECTION OP BENZOIC ACID. 



The methods given below are equally applicable to benzoic acid and 

 saccharin, and are only characteristic in the absence of the latter. The 

 methods given under saccharin, however, are not applicable to benzoic 

 acid. In case the two substances occur together, advantage is taken 

 of the fact that benzoic acid is volatile with steam while saccharin is 

 not. In this case about 200 cc of the sample are acidified with 5 cc of 

 a 20 per cent solution of glacial phosphoric acid and distilled almost 

 to dryness. The distillate is made slightly alkaline, evaporated to dry- 

 ness, and the residue treated according to any of the methods given 

 below for the detection of benzoic acid. The benzoic acid can onl} r be 

 completely volatilized, however, by leading a considerable quantity of 

 steam through the distilling flask. 



MoJiler's method. About 200 cc of the sample are made alkaline 

 with a solution of barium hydroxid, evaporated to about one-third of 

 its former volume, and filtered through a folded filter. The filtrate is 

 acidified with sulphuric acid and extracted with ether several times. 

 The ether is transferred to a porcelain dish, allowed to evaporate spon- 

 taneously, and the residue tested for benzoic acid by Mohler's method. 

 The details of this method are as follows: The residue is treated with 



