INCANDESCENT MANTLE LAMPS 97 



burner is about 80. The preparation of the gas is seldom 

 free from objectionable smell, but with good forms of 

 automatic generators and pure carbide this is very much 

 reduced, and no trouble or danger need be anticipated. 

 It is a good plan to have a " purifier " connected up be- 

 tween the generator and jet, as it materially increases the 

 brightness of the light. The purifier is merely a box con- 

 taining pieces of asbestos on which water is deposited 



Fig. 29 



INCANDESCENT GAS LAMP 



from the gas ; it may form part of the tray which carries 

 the jet. 



Incandescent Gas. Incandescent gas is probably the 

 most largely used of any illuminant, and possesses many 

 advantages as regards simplicity and convenience. The 

 chief objection to it is the difficulty of getting critical 

 illumination without the formation of an image of the 

 mantle. For work other than critical it is quite efficient, 

 although not very intense ; the inverted form is generally 

 to be preferred. Fig. 29 illustrates a convenient vertical 



