294 



ELEMENTARY CHEMICAL MICROSCOPY 



clamp open when removing or changing the object slide serving 

 as a cover. 



Instead of holding the watch glass and cover, at the edges, 

 between the thumb and finger as described above, the clamp 

 shown in Fig. 154 may be used, or two watch glasses with ground 



FIG. 154. 



edges selected to fit edge to edge may be clamped together. In 

 certain instances either one of these watch glass methods may 

 prove to be more practicable than the crucible. In all cases, 

 however, the clamp support is far superior to the fingers. 



Although the device just described may be satisfactorily 

 applied to the fractional distillation of small amounts of volatile 

 liquids, small distilling tubes will be found in certain cases to be 

 somewhat safer for very volatile substances. These are readily 

 made from small glass tubing of thin wall as shown in Fig. 155. 

 The finished distilling tube is shown in A. To introduce the 

 liquid to be distilled a rubber pipette cap r is slipped over the 

 large end of the tube (Fig. 155 B) ; the tube is inverted as shown, 

 the drawn-out end of the tube is dipped into the liquid to be 

 distilled and the rubber bulb is compressed just enough so that 

 when released the liquid will rise into the bulb in sufficient 

 volume to not quite half fill it. The tube is then again turned 

 to the position A, the bulb surrounded by ice and the drawn-out 

 tube sealed off in the flame of a blast lamp or blow pipe. The 

 bulb is removed from the ice, wiped dry and the apparatus 

 arranged as shown in Fig. 155 C. The liquid may now be heated 



