MICROSCOPIC TECHNIQUE AND REAGENTS. 771 



almost any size desired. And it will be found that these isolated 

 crystals may be quite as easily prepared as the aggregates which 

 seem so characteristic to- the average student. Special methods, 

 however, may be necessary to obtain such isolated crystals. For 

 instance, single crystals of menthol (Fig. 126) are obtained by 



FIG. 424- Piperine: monoclinic crystals, mostly on the clinopinacoid, showing the oblique 

 terminations, obtained from hot alcoholic solution. 



means of sublimation rather than from solutions. Cumarin 

 crystals are easily obtained by controlling the temperature of the 

 melted mass, etc. 



The interest in these crystalline substances is becoming greater 

 as foods and drugs and technical products are subject to stand- 

 ards of purity. Most of the crystalline constituents common to 



