nitrogen and oxygen combine to form nitric oxid. This unites directly with more oxygen forming nitrogen dioxid, which when dissolved in water gives a mixture of nitric and nitrous acids. A very high temperature is necessary to cause the first union of nitrogen and oxygen, and at this temperature equilibrium is established when less than two per cent, of the nitrogen is oxidized. At a somewhat lower temperature the nitric oxid is decomposed into nitrogen and oxygen, so that it is no simple matter to cool this nitric oxid from the temperature at which it is formed, without having it completely decomposed in the process. This has, however, now been successfully accomplished at Notodden, where I was given an opportunity of inspecting the plant. A peculiar form of electric furnace is used, in which a flaming arc is driven back and forth along copper electrodes by electro-magnets. Through this arc air is blown, and in its passage a small proportion is converted into nitric oxid. It passes so quickly that very little of that which has been formed is decomposed, but on the contrary it is by the excess of air present converted into the dioxid.
The gases coming from the furnaces are cooled by passing through pipes in boilers, and thus incidentally furnish more steam than is needed for the whole plant, completely eliminating the item of coal, usually such an important part of the cost of manufacture in all industrial plants. The gases are then passed up large towers filled with broken quartz, down which water trickles. The oxid of nitrogen is absorbed, furnishing a dilute nitric acid. This is then pumped to large
