NITRATES FROM ATMOSPHERE ^SCOTT. 



373 



a yard. At each half-period of the alternating current a fresh arc 

 forms, so that the result is the equivalent of a triangular sheet of 

 flame. 



An important feature is that the wall which divides the two parts 

 of the furnace is hollow, and gas and air which has been through tlie 

 furnace previously and been cooled is blown tlirough this central 

 passage. As will be no- 



CetiiAirSurnf' 



C93 4 M)r.0ot1et 



ticed from figure 5, this 

 cool gas and air strikes into 

 the top of the arc flame, 

 and it serves to cool the 

 gases which have just been 

 formed. The two arcs are 

 in series, and the furnaces 

 work in sets of three — one 

 to each phase. Each fur- 

 n a c e , therefore, receives 

 single-phase current at 

 6,000 volts, 50 periods per 

 second. 



At Gelsenkirchen there are 

 24 suchfurnaceSjeachtaking 

 400 kilowatts at 4,000 volts. 



The arcs are started by 

 means of copper starting knives, which can be approached to within 

 a few millimeters at the bottom, when the two horns come together. 

 When the arc has been started, these starting knives are withdrawn, 

 and the larger space between the electrodes is then sufficient to let 

 the hot air from the tuyere pass through freely. The starting knives 

 last 20 hours, whereas the main electrodes, which are of steel and 

 water cooled, last 200 hours. 



The works of La Xitrogene Cie, at La Roche-de-RamCj Hautes 

 Alpes, France, have nine Pauling horn-arrester furnaces of 600 horse- 

 power each in operation, and nine more, of 1,000 horsepower each, are 

 being added. 



The general layout of the plant is shown in figure 6, and it will 

 be noted that the furnaces are arranged in sets of three— one furnace 

 to each phase. 



The fresh air for the furnaces is supplied by a 250-horsepower 

 turbo-compressor, running at 3,000 revolutions, and before it gets 

 to the furnace tuyeres it passes through a preheater. The air travels 

 through the furnace at 1,200 feet per second. 



When the gases come from the furnaces their temperature is about 

 1,000° C, and the nitric-oxide content 1.15 to 1.5 per cent. They 

 first pass through the preheater, and give up some of their heat to 

 the fresh air going to the furnaces. 



