342 ODOIIOGRAPHIA. 



at the same time becoming somewlmt heated and assuming an 

 emerald o-reen colour. As soon as this reaction has ceased, the 

 liquid must be gently distilled. Salicyl aldehyde then passes over 

 and condenses in the receiver in the form of a heavy oil, its 

 formation being accompanied by the evolution of carbonic anhydride 

 and formic acid. The distillation is continued until the condensed 

 water is no longer milky, and passes over quite clear. If the 

 distillation be continued too long, furfural passes over, and all 

 preparations made from the aldehyde then become intensely red- 

 coloured on standing. The oily portion is then separated from the 

 water and the portion which remains dissolved in the water may 

 be extracted by agitation with ether and evaporation of the ether. 

 The residue in the retort is chrome alum, on the surface of which 

 there usually floats a resinous matter resulting from the decompo- 

 sition of part of the salicyl aldehyde. 250 grams, of salicin thus 

 treated, yield about 60 grams of salicyl aldehyde. 



The aqueous extract of willow bark may also be used instead of 

 pure salicin. The aldehyde thus obtain is purified by combining it 

 with an alkali, concentrating the solution and distilling it with 

 dilute sulphuric acid. 



Salicyl aldehyde was at first mistaken for an acid (spiroeic acid 

 or salicylous acid), because it is at once an aldehyde and a phenol 

 and therefore forms salts. 



Salicyl aldehyde also occurs in the sap of various plants 

 belonging to the genus Spircea ; in the stem and root of Crepis 

 fcetida,* and in the krvai of chrysomela pojndi, which lives on 

 willows and poplars and possesses small openings along the body 

 from which salicyl aldehyde may be pressed out in oily drops.f 

 Enz also obtained it by distilling the beetle with water. J 



Salicyl aldehyde is a liquid with a pleasant aromatic odour and 

 a burning, spice-like taste ; it boils at 196^-5 C, solidifies at 20° 

 C. to large crystals, and has a sp. gr. of 1"1731 at IS^'o. Its 

 aqueous solution, even when very dilute, is coloured violet by 

 ferric chloride and yellow by alkalies. It does not reduce 

 Fehling's solution^ and forms difficultly soluble compounds with 



* Ann. Cheni. Pharm., xci., p. 374. 

 t Jahresber. Chem., 1850, p. 583. 

 ::: Ann. Chem. Pharm., 1859, p. 312. 

 § Ber. Deutsch. Chem. Ges., ix., p. 824. 



