16 



BUNSEN'S BURNER. 



In one variety the spirit holder is separated from the burner, in 

 the other it surrounds it. The burner, when not in use, must be 

 covered by a cap, otherwise the alcohol evaporates, while water 

 collects in the wick, and renders it difficult to light it again. The 

 ground-glass caps crack very easily, and may be replaced by 

 loosely fitting brass caps. 



The flame of common coal gas deposits soot on objects held into 

 it. A special contrivance, called a Bunsen's burner (figs. 18 and 19), 

 is therefore required if gas is used for heating purposes. It con- 

 sists of a common jet with several fine holes a (fig. 18, I?), which 



(i real size). 



FIG. 18. 



(| real site). 



is surrounded by a tube of metal b b, at the bottom of which are 

 openings for the admission of air, c c. The gas which issues from 

 the jet becomes thus mixed with air, and burns at d with a non- 

 luminous flame, which is without smoke, resembling the flame of a 

 spirit lamp, but much hotter. The gas is supplied through a short 

 horizontal tube, which is connected with a gas pipe by means of a 

 piece of India-rubber tubing. If necessary, the tube may be 

 slipped over a common burner in the manner shown in fig. 20, 

 which prevents the tube from forming a sharp bend. It is con- 

 venient to have a stopcock attached to the horizontal tube. The 

 gas should only burn at d, but never within the tube, at a. If 

 the flame cannot be reduced without receding into the tube, the 



