26, 27. SALICYLIC, BENZOIC ACID, ETC. 25 



tinguished by their behaviour to ferric chloride, with which 

 salicylic acid strikes the well-known violet colour. Benzoic acid 

 may be easily sublimed between watch-glasses. Dissolved in a 

 drop of ammonia, the excess of which is allowed to evaporate by 

 exposure to the air, a drop of ferric chloride produces a brownish 

 tinge. 



Cinnamic acid may also be similarly distilled over, and separated 

 from the distillate. It may be distinguished from both the fore- 

 going acids by its behaviour to oxidizing agents such as perman- 

 ganate of potassium, with which an aqueous solution yields on 

 warming oil of bitter almonds, whereas benzoic acid yields the 

 same product when acted upon by a reducing agent such as 

 sodium -amalgam. (See also 38.) 



Any cinnamic acid present might in certain cases have been 

 produced from ethereal salts, such as, for example, styracin 

 {cinnamate of cinnamyl), or cinnamein (cinnamate of benzyl). 

 Both of these compounds are soluble in petroleum spirit, and are 

 resolved, by decomposition with an alkali, into cinnamic acid and 

 the respective alcohol Styracin crystallizes in needles, which, 

 according to Scharling, 1 melt at 44. Cinnamein is liquid at the 

 ordinary temperature. The former has an odour resembling 

 vanilla, the latter a faint smell of balsam of Peru. 



If one of the three acids mentioned has been isolated, special 

 care should be taken to ascertain whether the corresponding 

 aldehyde is also present in the aqueous liquid, viz., salicylic, benzoic 

 {oil of bitter almonds), or cinnamic aldehyde, and whether the acid 

 has not been produced from the aldehyde by absorption of oxygen 

 during or after distillation ( 33). 



27. Physical Properties. The principal part of the oil ob- 

 tained by distillation should be completely freed from moisture, 

 filtered and tested with regard to its consistence. If, on standing 

 some time in a freezing mixture, a crystalline constituent be 

 deposited it should be separated and examined by itself. The 

 action of the oil on polarized light should be observed ( 141), and 

 fluorescence looked for ; if present, it should be ascertained whether 

 warm water will remove a substance fluorescent either alone or on 



1 Annalen d. Chemie u. Pharra. Ixviii. 168. See also Riigheimer Disserta- 

 tion, Tubingen, 1873 ; Kraut, Annalen der Chemie u. Pharm. clii. 129 (1S69) ; 

 <Amer. Journ. Pharm. xlii. 236) ; and Von Miiller, Ber. d. d. chem. Ges. Jg. 

 1876, 274. 



