ADDITION OF ANTISEPTICS 65 



The alcoholic liquid is neutralized with baryta water 

 and evaporated to about 10 c.c. Dilute sulphuric acid is 

 again added and the liquid is shaken 3 or 4 tunes with a 

 little ether, which is collected each time with a pipette. 

 The ether is evaporated and the benzoic acid remains in 

 almost pure condition. The mass is dissolved in a little 

 warm water and a drop of a solution of sodium acetate 

 and a drop of a neutral solution of ferric chloride are 

 added. If benzoic acid be present, a reddish sediment 

 of benzoate ferric oxide appears (Meissl) ; or a little of 

 the dried mass may be treated with a drop of concen- 

 trated nitric acid, the latter evaporated and the residue 

 mixed with sand and heated to a high temperature in a 

 glass tube. The benzoin is indicated by the odor of 

 bitter almonds (nitrobenzol). 



[The method of Peters, as given by Leffrnann, is as 

 follows: " The material is made slightly acid and ex- 

 tracted with chloroform, which is then evaporated spon- 

 taneously. The vessel containing the residue is placed 

 in melting ice, 2 c.c. of sulphuric acid added, and stirred 

 until the residue is dissolved. Barium dioxide is dusted 

 into the mass, with constant stirring, until the liquid 

 begins to foam, when 3 c.c. of hydrogen dioxide (3 per 

 cent.) are added drop by drop. The dish is then re- 

 moved from the cold bath, the contents diluted with 

 water to convenient bulk, and filtered. The acid filtrate 

 is extracted with chloroform. The benzoic acid will have 

 been converted into salicylic acid by the process and the 

 latter may be detected by dilute solution of ferric 

 chloride or ammonio-ferric sulphate. " L.P.] 



d. Potassium bichromate is used by chemists as a 

 preservative for milk samples. It is seldom used as a 

 preservative of market milk. This poisonous material is 

 easily detected, if one mixes together equal quantities 

 of milk and of a 1 per cent, solution of nitrate of silver. 

 5 



