446 



NA TURE 



[August 30, 1906 



It is interesting to note that the flame, considering 

 its liigh electrical power, is not particularly luminous, 

 as it is quite possible to look directly at it with the 

 naked eye at a distance of about i yard, and it is not 

 easy to snapshot it. 



The alternating-current disc flame is enclosed in 

 special furnaces which are lined with firebrick and 

 enclosed with metal casing. The fire-chamber of the 

 furnace is narrow in the direction of the lines of 

 force — from 5 cm. to 15 cm. wide — and made partly of 

 perforated firebrick, the air being conveyed to the 

 flame in an evenly distributed supply through the 

 walls. The magnetic system is composed of two 

 powerful electromagnets, the extremities of which are 

 turned in towards the fire-chamber. The air is driven 

 into the central region on both sides of the flame by 

 gentle pressure from a Roots blower ; it must not be 

 blown too rapidly, otherwise the flame is extinguished. 

 Fig. 4 shows three of the furnaces, each furnace 

 taking 500 kilowatts. The volume, of air at present 

 treated is 75,000 litres per minute, w'hich after passing 

 through the furnace contains about i per cent, of 

 nitric oxide. The gases leave the furnace at a tem- 

 perature of 600° to 700° C, and are first passed 

 through a steam boiler, the steam from which is em- 



calcium nitrite obtained from the fifth tower and to 

 convert unchanged lime into nitrate. The oxides of 

 nitrogen produced by the decomposition of the nitrite 

 are carried back to the system of towers. The solu- 

 tion resulting is run, together with the rest of the 

 stored-up acid, into another series of granite tanks, 

 where it reacts with limestone, thus producing neutral 

 calcium nitrate. This solution is evaporated down 

 until the temperature rises to 145°, answering to a 

 concentration of 75 to 80 per cent, of calcium nitrate. 

 The solution is then run into 200-litre drums, where it 

 solidifies, and it appears on the market in this form. 

 It is, however, found that for fertilising purposes it 

 is better to use the basic nitrate owing to the 

 extremely hygroscopic properties of the neutral salt. 

 The ground-up basic nitrate can, as it is not hygro- 

 scopic, be readily scattered with a sowing machine. 



Numerous manuring experiments have been made 

 with calcium nitrate at different agricultural institutes. 

 The results show that lime saltpetre is quite as good 

 as Chili saltpetre, and on a sandy soil is even superior. 



The yield of anhydrous nitric acid by the Birke- 

 land-Eyde process is between 500 and 600 kilograms 

 per kilowatt year. The cost of calcium nitrate con- 

 taining I3'2 per cent, of nitrogen is about 4?. per ton. 



Fig. 3. — Photograph of electric arc flame, shewing i 



f-cooled electrodes. 



ployed in the further manufacture of calcium nitrate. 

 .\fter passing from the boiler the temperature is about 

 200°, and by passage through a cooling arrangement 

 the temperature is reduced to 50°. 



The gases now pass into two large oxidising 

 chambers with acid-proof lining, where the oxidation 

 of the nitric oxide formed in the furnaces takes place 

 with production of nitrogen peroxide. It is then con- 

 ducted into an absorption system consisting of five 

 towers, two being of granite and two of sandstone, 

 filled with broken quartz over which water trickles, 

 nitric acid thus being produced. The fifth tower is 

 filled with broken bricks over which milk of lime 

 trickles and which absorbs the now rarefied nitrous 

 gases with formation of calcium nitrate and nitrite. 

 In the plant at Notodden there are two such series of 

 towers. The liquids from the fourth tower, which 

 consist of 5 per cent, nitric acid, are raised to the top 

 •of the third tower by compressed air, those from the 

 third to the second, and from the second to the first. 

 The acid, on leaving the third tower, is of 15 per 

 cent, strength, on leaving the second 25 per cent., and 

 it leaves the fourth tower with a strength of 50 per 

 cent. 



Some of the acid produced is used to decompose the 



NO. 1922, VOL. 74] 



Fig. 4. — Photograph of three 5oo-ki!owatt furnaces at Notodden. 



and the selling price about 8L per ton. New works 

 of 30,000 h.p. are now nearly completed, and it 

 is hoped that the new factory will be very shortly in 

 active operation. To an Englishman it is of interest 

 to notice that a\\ the pioneer work was carried out 

 in this country. In this connection it should be 

 remarked that even if the final stage — the application 

 of the flame electric arc — had been tried in this 

 country, it could not have been a commercial 

 success. To be a commercial success it is absolutely 

 essential that very cheap power should be at the dis- 

 posal of the manufacturers. At present we have not 

 this cheap power, and it is very improbable that we 

 shall have it in the near future; unless, indeed, some 

 engineer can show us how to harness the tides. But 

 if we cannot manufacture nitric acid from the atmo- 

 sphere there is a problem, probably a very difficult pro- 

 blem, the elucidation of which would be of almost 

 untold value, and that is the fixation or utilisation of 

 the nitrogen in sewage, which at present is almost 

 entirely thrown with happy abandonment into the sea. 

 As a consequence, the mouths of rivers are polluted, 

 fish are destroyed, and, what is perhaps more serious, 

 disease is often disseminated. 



F. MoLLWo Pkrkin. 



