MICRO-ANALYSIS. 853 



Vanillin, or the methyl ether of protocatechuic aldehyde, 

 CgHs.CHO.OCHg.OHCi, 3, 4), is not found in the plant king- 

 dom as such but appears to be formed as a result of the decom- 

 position of other substances. It is prepared from vanilla pods, 

 potato paring-s and Siam benzoin. The commercial article is 

 prepared synthetically from eugenol, guaiacol and coniferin.* 



The M. P. is 8o-8i C, which serves to distinguish it 

 from cumarin which has a M. P. 67 C. ; acetanilide (M, P. 

 113) ; and benzoic acid (M. P. 120 C). At 80 C. one part 

 of vanillin is soluble in 15 parts of water and very soluble in 

 alcohol, ether, chloroform and glycerin. The individual crystals 

 from hot aqueous solutions vary in length from 0.3 mm. to 4 

 mm. (Fig. 128). 



Vanillin. Crystals from hot aqueous solutions. 



Orthorhombic : a: b = 0.560: i. 



Forms observed: Base (001); brachypinacoid (010); unit 

 prism (no); brachydome (oic) ; and pyramid (iic). These 

 two latter forms are doubtful. 



Angles: Angles iioAiIo = 58 30'. 



Habit: Tabular on the base, elongated along the a axis, the 

 ratio of length to width being 10: i or over. The end of the 

 crystal is terminated by the unit prism, the two faces of which 

 are often unequally developed, one face being sometimes entirely 

 absent so that the termination is oblique. 



Optical properties: The a axis is that of least refractive 

 index for the basal aspect. An interference figure is observed 

 on the base showing that the c axis is a bisectrix, and the axial 

 plane is probably the brachypinacoid. .If this is the case the 

 optical orientation is a = a; tl = b; 1="^. 



* Oesterle, Grundriss der Pharmakochemie, pp. 261-268. 



