490 
NATURE, 
isis: “ris nome 
THE MANUFACTURE OF NITRATES FROM 
THE ATMOSPHERE.* 
Pauling Furnace. 
“THIS furnace was invented by Mr. H. Pauling, of 
Gelsenkirchen, and he took the idea from the 
well-known horn-break lightning arrester (see Fig. 4). 
It has two hollow iron electrodes, arranged to form a 
Fic. 4.—Arc flame between horn electrodes. From photograph by Mr. Lustgarten of Manchester. 
V, which at the lowest point is about 4 cm. across, as 
shown in Fig. 5. At this point there are two 
lighting Iknives, which can be approached to within 
a few millimetres, and are readily adjustable. The 
are strikes across and runs up the diverging elec- 
trodes by reason of the natural convection currents 
1 Abridged from a paper sead before the Royal Society of Arts on May 15 
by Ernest Kilburn Scott. Continued from p. 465. 
NO. 2228, VoL. 89] 
and the repelling action of its own magnetic field, 
ut principally because of a blast of heated air from 
an air-duct immediately below. The are diverges as 
it follows the shape of the electrodes, and it attains 
a length of about a yard. At each half-period of 
the alternating current a fresh are 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 fur- 
nace is hollow, and gas 
and air which has _ been 
through the furnace pre- 
viously and been cooled is 
blown through this central 
passage. As_ will be 
noticed from Fig. 5, this 
mixture of cool gas and air 
strikes into the top of the 
arc flame, and 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 furnace, therefore, 
receives single-phase cur- 
rent at 6000 volts, fifty 
periods per second. 
At Gelsenkirchen there 
are twenty-four such fur- 
naces, each taking 4oo kw. 
at 4000 volts. 
The arcs are started by 
means of copper starting- 
knives, which can be ap- 
proached to within a few 
millimetres at the bottom, 
where the two horns come 
together. When the arc 
has been started, these 
starting-knives are with- 
drawn, and the larger 
space between the  elec- 
trodes is then sufficient to 
let the hot air from the 
tuyere pass through freely. 
The | starting-kknives last 
twenty hours, whereas the 
main electrodes, which are 
of steel and water-cooled, 
last 200 hours. 
The works of La Nitro- 
géne Cie., at La Roche-de- 
Rame, Hautes Alpes, 
France,, have nine Pauling 
horn-arrester furnaces of 
600 horse-power each in 
operation, and nine more 
of 1000 horse-power each 
are being added. 
The general lay-out of 
the plant is shown in 
Fig. 6, and it will be noted 
that the furnaces are ar- 
ranged in sets of three, 
one furnace to each phase. 
The fresh air for the furnaces is supplied by a 
250 horse-power turbo-compressor running at 3000 
revolutions, and before it gets to the furnace tuyéres, 
it passes through a preheater. The air travels 
through the furnace at 1200 ft. per second. 
When the gases come from the furnaces their 
temperature is about 1000° C., and the nitric oxide 
content 1-15 to 15 per cent. They first pass through 
