JULY ay 1972) 
NATURE 
491 
the preheater, and give up some of their heat to the 
fresh air going to the furnaces. 
The gases then pass through the two cooling towers 
which are outside the furnace-house. Each of these 
towers is 16 ft. in diameter and qo ft. high, and filled 
with fire-brick. When the bricks of one tower have 
become hot the gases are switched over to the other 
tower. Fresh air is then drawn through the heated 
tower by means of the chimney (85 ft. high), and the 
brickwork in it is thus cooled. 
The gases are sucked out of the cooling tower by 
a 15 horse-power fan and forced into the oxidation 
tower, which is built of reinforced concrete, and 
measures 33 ft. diameter and 75 ft. high. Here the 
temperature having fallen to 600° C., oxidation to 
NO, goes on rapidly. 
From the oxidation tower there are two pipe-lines, 
and one takes some fixed gas and air back to the 
furnaces, where it is passed through the central 
passage and comes in contact with the freshly fixed 
nitrogen at the top of the arcs. In this way the 
fresh gas is cooled without being diluted. 
A second pipe-line of aluminium takes the re- 
mainder of the gases to the absorption towers, each 
Gas 4AirDutier Gas & Air Outlet 
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FIG. 5. 
of which contains 250 tons of stoneware packings. 
The gases pass from 1 to 5, whilst the water, gradu- 
ally accumulating more and more acid, flows in the 
opposite direction, namely, 5 to 1. . Montejus operated 
by compressed air raise the solution to the top of the 
different towers. 
The gases from No. 5 absorption tower still con- 
tain a small amount of NO and NO,. They are 
passed through an acid filter, in which the last traces 
of acid are condensed, and then pass to the nitrite 
towers. These contain sodium-carbonate solution, and 
the gases react with it to form sodium nitrite, having 
a concentration of 20 per cent. This is submitted to 
evaporation, the hot furnace gases being used for 
the purpose, and white sodium-nitrite crystals are 
obtained containing 95 per cent. of nitrite and 3 per 
cent. of nitrate. 
Some idea of the efficiency of the plant may be 
obtained from the fact that Mr. Pauling guarantees 
60 grams of too per cent. HNO, per kw.-hour of 
electrical energy, measured at the entrance of the 
electric transmission line into the factory, and also 
that the electro-chemical plant proper will cost. about 
120 francs (51.) per kilowatt. 
The Southern Electro-Chemical Co. of Nitrolee, 
NO. 2228, VOL. 89 | 
' South Carolina, in the United States, has a 4000 
horse-power plant on the Pauling system for manu- 
facture of calcium nitrate. Electric energy is 
generated by two water-power plants at Great Forks 
and Rocky Creek. 
Calcium Cyanamide. 
The discovery of calcium cyanamide came about 
as the result of a research by Dr. Franck and Dr. 
Caro, who were following on the lines of some 
previous work of Playfair and Bunsen. Their 
immediate object was to make cyanide of potassium 
for the recovery of gold from tailings, and they 
incidentally found that barium carbide absorbed 
nitrogen to form barium cyanamide. By using 
calcium carbide they obtained a similar reaction 
according to the formula 
CaC, +2N—CaCN,+C. 
It was then found that by treating calcium cyanamide 
with hot water it gave off ammonia according to the 
equation 
CaCN,+3H,O0—CaCo, +2(NH,), 
and this gave rise to the idea of using it as a manure. 
As carried out at the Odda Works, the calcium 
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Fic. 6. —The lay-out of the works by La Nitrogéne Cie, France. 
carbide, broken into pieces, is delivered to crushing 
machines, from which it passes to mills in which it 
is ground fine, the whole of these operations being 
effected automatically in an air-tight plant so as to 
prevent acetylene gas being given off. It is of interest 
to note that the glowing mass from, the calcium 
carbide furnace cannot be used straight away. 
The powder is then filled into electric furnaces, of 
which, in the first installation at Odda, there were 
196, each holding 300 kg. : 
Fig. 7 is a rough sketch of the furnace, and it will 
be noticed that down the centre there is a cardboard 
tube to provide a space for the carbon pencil. After 
the carbide has been filled in, the carbon pencil is 
fixed in position, and the lid fastened down and made 
air-tight. 
Alternating current is now switched on, and the 
temperature is raised to 800° to 1000° C. The card- 
board tube and certain cardboard partitions which 
had been placed in the furnace when the calcium 
carbide was run in, are burnt up, and they leave spaces 
allowing the nitrogen gas, which is there admitted 
under pressure, to circulate freely. Electric current is 
kept on for twenty-five hours, and at the end of thirty- 
five hours all the nitrogen has been absorbed as shown 
by the meter being stationary. 
