13 



Sufficient mercury to fill the tube 3 or 4 inches is introduced by the 

 aid of a funnel such as shown in Figure 13, except that the slender 

 stem need be only 2 or 3 inches long. In the absence of such a funnel 

 it is quite as well to employ a small paper cone of the kind commonly 

 used in filtering mercury. The mercury in the tube is then boiled 

 carefully over a good Bunsen burner flame. (See fig. 14.) For this 

 purpose the tube is held easily in the hands and moved continuously 



Figure 13 Figure 14 



Funnel tube and boiling method of filling barometer tubes 



through the flame and rotated so as to avoid undue local heating of 

 the tube. As the heating proceeds the air and moisture vapor first 

 form in minute silvery-white bubbles, giving the tube a frosted ap- 

 pearance. These enlarge, and after actually boiling the mercury for 

 a while all evidence of formation of bubbles on the walls disappears, 

 and further boiling of the mercury takes place with sudden bursts 



