II. CHEMISTRY 



467 



(c) Crystal Structure. The detailed crystal structure of nicotinamide has 

 been investigated by Keenan,^^ by McCrone and Cook/^ and b,v Wright 

 and King.^- Keenan reported that nicotinamide crystallized in colorless 

 small rods which exhibited both parallel and obliciue extinction. He gives 

 the follo\\ing values for the refractive indices: a equal to 1.485 ± 0.002 

 and 7 greater than 1.734. McCrone and Cook encountered considerable 

 difficulty m preparing crystals suitable for microscopic examination but 



TABLE V 



Some Esters of Nicotinic Acid (adapted from Badgett el ul.^^) 



finally obtained crystals from ethylene glycol on a microscopic slide, as 

 shown in Fig. 3. In addition they found any one of four polymorphic forms 

 when nicotinamide was crystalhzed from a melt, two of which are shown 

 in Fig. 3. Nicotinamide I recrystallized from common solvents appeared 

 as long, prismatic monoclinic rods showing well-developed prisms and 

 domes. McCrone and Cook present the various measurements of the crystal 

 morphology and crystal optics of nicotinamide I. The density was 1.401 ± 

 0.002 (g. cm.~'^) as determined by a buoyancy method using carbon tetra- 

 chloride and petroleum ether. 



" W. C. McCrone, Jr., and J. W. Cook, The Frontier 10, 12-23 (1947,). 



