HANDLING SMALL AMOUNTS OF MATERIAL: DISTILLATION 293 



thumb and forefinger, place a cooling drop of water upon the top 

 of the slide and heat the watch glass gently over a micro-flame 

 (Fig. 152) until vapors begin to con- _ 

 dense upon the object slide. Heating 

 to violent boiling must be avoided. 

 The cooling drop upon the upper sur- 

 face of the object slide is removed, 

 the slide raised from the watch glass 

 and turned over with a quick move- 

 ment. The proper reagents for dis- FlG - T 5 2 - Watch-glass Method 



,1 r ,1 .*. f Distillation. 



closing the presence of the constituent 



being sought are added and the resulting preparation examined 



with the microscope. 



The method just described is applicable only to easily vola- 

 tilized substances and where prolonged heating is unnecessary, 

 but even in expelling ammonia, the fingers become uncomfort- 

 ably hot. To avoid this discomfort the distilling device shown in 

 Figs. 153 and 154 may be employed. It consists of a tiny glass 



FIG. 153. Apparatus for Microchemical Distillations. (Slightly Enlarged.) 



crucible C, whose upper edge is ground smooth and true, a sup- 

 porting clamp made of spring brass wire W and an ordinary 

 short object slide O. The component parts are shown in Fig. 

 154, and the apparatus in use in Fig. 153. Just as in the watch 

 glass method fibrous asbestos or glass wool is employed as an 

 absorbent, an acidulated or alkaline drop serves to retain the 

 volatile constituent and a cooling drop is placed upon the upper 

 surface of the condensing slide. A lever L serves to keep the 



