No. 6. DEPARTMENT OF AGRICULTURE. 418 



anj other. For it is a question of how much gas can actually come 

 in contact with the flame in a given time and be heated to the re- 

 quired temperature. The oven in which this arc-flame is generated 

 has the shape of a cheese standing on edge, and is of considerable 

 size, since the flame", formed bj the electric current already men- 

 tioned, is six feet in diameter. On the other hand the flame is ex- 

 tremely thin (only a couple centimeters thick) so that while the inner 

 chamber is a little over six feet one way, it is only a couple inches 

 the other way. Around the flame is firebrick containing air chan- 

 nels and perforations through which the air current is forced into 

 the flame, and is again collected into an outlet located close to the 

 inlet opening. The air as it leaves the oven is highly colored on ac- 

 count of the nitrogen tetroxide (NO2) fumes which are formed when 

 the air leaves the oven. This thin arc flame has a temperature of 

 about 3,000°C., but the gases as they leave the oven have a temper- 

 ature of about 700°C. Air passes through the oven at the rate of 

 25,000 liters a minute, that is, in the three ovens at Notodden 75,000 

 liters (about 75,000 quarts) air are treated each minute. 



At 3,200 degrees, absolute temperature, according to "Nernst," 

 the formation of 5 per cent, nitric oxide (NO), by volume, should be 

 possible. These ovens were tested with the following results: Dur- 

 ing several consecutive days and nights the gases leaving the oven 

 were found to have a temperature of 700° C, and the nitric acid 

 (ILNO3) obtained per liter gas, reduced to 0° and 760 m.m. pressure, 

 was 30 milligrams. This corresponds to 1.06 per cent, nitric oxide 

 by volume in the gas, which is equivalent to 4.58 per cent, nitric 

 oxide (NO) by volume in the gas while it is exposed to the arc 

 flame. 



At the high temperature of the arc flame only nitric oxide is form- 

 ed, the temperature is too high for nitrogen tetroxide (NO2), and 

 the nitrogen trioxide (N^O.j) to exist. The nitric oxide which is 

 formed and is present in the air as it leaves the oven must be oxi- 

 dized to higher oxides. This oxidation takes place of its own ac- 

 cord in the presence of air (N0+0=N02), and the nitrogen tetrox- 

 ide in the presence of water is changed into nitric and nitric acids, 

 as shown by the following equation: 2 NOo+HoO=HN03+HN02. 

 At the existing high temperature the nitrous acid is decomposed 

 into nitric tetroxide, nitric oxide and water thus: 2HN02=N02+N0 

 +H2O, and these residual gases must again be changed into nitric 

 acid. A residue of gases is therefore always present. 



Method of Changing the Nitric Oxide (NO) into the Marketable 

 Products. — When the gas mixture leaves the oven it has a tempera- 

 ture of between 600 and 700° C. The hot gases, in order to utilize 

 the heat they carry, are conducted through a steam boiler generat- 

 ing steam to be used later in the process. Here the gases are cooled 

 down to about 200° C, and are next led through a cooling apparatus 

 where they are reduced in temperature to about 50° C. From this 

 cooling apparatus the gases enter a large iron tower or cylinder, 

 called "oxidation cylindw," which is coated on the inside with a 

 paint preparation which resists the acid. This cylinder holds about 

 12 cubic meters (about 15 cubic yards) and therefore gives the air a 

 little time to oxidize; it being changed about 6 times a minute. 

 Next the gas mixture passes in the absorption system which is com- 

 posed of stone towers 2X2X10 meters inside diameter. There are 



