246 



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. 131 may be used, or two watch glasses with ground 



FIG. 131. 



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 of the form suggested by Behrens 1 

 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. 132; the different steps in 

 the preparation are indicated in i, 2, 3, 4 and 5. The finished 

 distilling tube is shown in A. To introduce the liquid to be dis- 

 tilled into one of the tiny bulbs, fuse the end of one of the project- 

 ing tubes, cool thoroughly and introduce the end of the open tube 

 into the drop of liquid, warm the upper bulb to drive out air and 

 allow to cool with the tube still dipping into the liquid. If an 

 insufficient quantity of the liquid enters, heat again just enough 

 to drive out all but a trace of liquid, then dip the end below the 

 liquid to be tested and heat the lower bulb until the contents are 



1 Anleitung z. mikrochem. Anal. (2 Auf.), p. 140. 



