106 MANAGEMENT OF THE LIME LIGHT [CH. IV 



opens; then the mixed gases burn on emergence from the nozzle 

 (fig. 59). This form of jet gives the greater amount of light but 

 the two gases should be under considerable pressure. The tip of 

 the nozzle (fig. 59 N) makes an angle of 40 or 45 degrees with the 

 lime. This gives a source of light above the tip of the nozzle, and 

 hence there is free passage for the light to the condenser. 



The blow-through jet is usually 10 to 15 mm. (y 2 inch) from the 

 lime while for the mixed jet the nozzle is within about 3 mm. (y% 

 inch) of the lime. 



MANAGEMENT OF THE LIME LIGHT 



159. Connecting the gases with the burner. This is accom- 

 plished by means of rubber tubes of thick walls, and the ends of 

 the tubes should be tied or wired to the supply pipes and to the 

 burner ( i59a). 



It is a great advantage to have the two parts of conducting tubes 

 of the burner of the same color as the gas tanks, viz., red for hydro- 

 gen and black for oxygen, then there will be less liability to error 

 in connecting the gas supply. 



It is only while using the gas that the cylinder valve (fig. 57 V) 

 should be opened. And in opening it care should be taken to open 

 slowly so that the sudden rush of the compressed gas may not injure 

 the pressure gauges or the reducing valve. 



When through with the cylinder at any time the cylinder valve V 

 should be closed. 



The pressure of the two gases should be about equal. This can 

 be arranged by the pressure reducing valve. Set this to give the 

 desired pressure, which ordinarily is equal to a column of water 

 about 28 to 50 cm. high (n to 22 inches) or 2 to 4 cm. of mercury 

 (^4 to 1^2 in. Hg) a pressure of .03 to .06 kilos per sq. cm. (.4 to .8 

 Ibs. per sq. in.). 



160. Lighting the jet. Turn on the hydrogen slightly and 

 light it with a match or a cerium-iron gas lighter, then continue to 



159a. Flexible metallic tubes. There is now available flexible metallic 

 tubing with rubber connections at the ends to use in place of rubber tubes for 

 conducting gases (fig. 60). 



