840 



BOTANY AND PHARMACOGNOSY. 



Menthol (C^qHsoO). 



Occurrence: See pp. 631, 632. 



Menthol, CgHg.CHg.OH.CaH^ (i, 3, 4), occurs in peppermint 

 oil only in the Isevorotatory modification.* It melts at about 42 

 C. and on cooling crystallizes in aggregates composed of fine 

 needles ( Fig. 337, B ) . Upon sublimation short rods are obtained 

 (Fig. 337, A) ; and if a slide of the aggregates is covered with an- 

 other slide large needles may be formed. Menthol is very soluble 

 in alcohol, ether and chloroform and sparingly soluble in water. 

 It separates from peppermint oil upon cooling. 



i 



Fig. 337. Menthol: A, individual crystals obtained by sublimation; B, the commonly 

 occurring aggregates of very fine needles. 



Menthol. 



Orthorhombic. 



Habit : Crystals appear as long needles without terminations. 



Optical properties : The long dimension of the crystal is 

 uniformly the direction of least refractive index. This is con- 

 firmed by the interference figure which may be seen in certain 

 aspects and shows that the axial plane is parallel to the long 

 dimension. If this long dimension is called the vertical axis we 

 therefore have l=c. 



* Gildemeister and Hofifmann, Die Aetherischen Oele. 



