46 



THE PRODUCTION AND USE OF LIGHT 



open the gas cock, letting the gas pressure into the manometer. With 

 the ruler read accurately the difference in the level of the water in 

 the two arms of the manometer. If convenient, permit the manome- 

 ter to remain in position so that you can quickly determine the pres- 

 sure several times each day for several days. Read often and record 

 the reading together with the data and the hour. If the pressure 

 varies considerably at different hours of the day, how do you account 

 for it? 



57. Gas Burners. Illuminating gas may be burned in open 

 jets or in incandescent burners, that is, within mantles. The 

 incandescent gas lamp is constructed on exactly the same 

 principles as the incandescent gasoline lamp. The gas is 



FIG. 27. Device for 

 determining gas pres- 

 sure. 



FIG. 28. Automatic 

 device for regulating 

 gas pressure, 



FIG. 29. An inverted 

 illuminating gas lamp. 



mixed with air in a tube below the burner. This tube is 

 therefore the MIXER. The mixture of gas and air passes 

 through a wire gauze at the top of the mixer and is burned 

 within the mantle, there producing a blue, or non-luminous, 

 flame but much heat. What, then, is the source of the light? 

 All burners are supplied with some device for regulating the 

 gas and air supply. Some burners are also supplied with an 

 automatic device for regulating the gas pressure (Fig. 28). 

 Recently several forms of inverted mantle gas lamps have 

 come into common use (Fig. 29). 



