9 8 



CHEMICAL FERTILIZERS 



arc is produced inside an iron tube of comparatively small 

 diameter. The air is given a rotary motion, so that the arc 



H 



L 



A 

 P 



EE 



FIG. 3. Nitric acid furnace. Scott-Pauling three-phase type. 



is the jet by which air is delivered into the furnace. 



is the wire conveying the pilot sparks which maintain the arc in action. 



The electric current is of very high tension from some kind of coil, 

 are two out of the three electrodes which supply the main current, and 

 are so placed that the arc which is formed at their nearest points is in 

 close proximity to the pilot sparks points, allowing the current of air 

 to drive the arc up into the furnace, 

 is the furnace, which is merely an empty space, allowing room for the 



flame to form. 



is the tubular steam boiler which generates steam from the hot flame 

 of the nitrogen below. The hot gases then pass upwards from the 

 boiler. 

 is the pre-heater which heats the water supply for the boiler by the 



gases which have passed through the tubes of the boiler B. 

 is the exit of nitrogen oxide, which passes away to the absorption 

 apparatus. 



