404 
NATURE 
[JuLy 4, 1912 
direct current flows round the coils to produce the | and the gas becomes permanently fixed. The nitric 
magnetic field. 
When an arc is struck between the electrodes it 
is at once deflected in a direction perpendicular to 
the lines of force, and the necessity of having alter- 
nating current applied to the electrodes will be 
appreciated from the fact that with direct current the 
arc would be deflected to one side only. As each 
electrode is alternatively positive and negative, the arc 
is projected outwards first to one side and then to 
the other, thus giving a disc of flame about 6 ft. 
in diameter. The speed at which the arc moves out- 
ward is extremely rapid, and as the formation of a 
new arc is practically instantaneous, it appears to the 
eye as a Sheet of flame. 
An inductive resistance is a very necessary piece of 
apparatus to have in series with the arc, because its 
self-induction automatically effects 
a displacement of phase according 
to the currents flowing, thus 
enabling the are to burn steadily. 
The writer assisted Mr. Howles 
with some experiments in fixation 
of nitrogen about thirteen years 
ago, and the necessity of having 
wer, an induction coil in circuit was 
then noted. Without it the arc 
could not be maintained steady. 
It should be noted that any 
furnace working with alternating 
current has necessarily a consider- 
able phase difference. In other 
words, the power factor is low, 
and therefore, in estimating the 
sizes of dynamos and cables, due 
allowance has to be made. This, 
of course, raises the cost of elec- 
tric energy. For ordinary power 
supply, a power factor of 0°85 is 
quite usual, but with fixation of 
nitrogen furnaces the power factor 
is only about 06. 
rer Flow 
<—_S 
Schonherr Furnace. 
This furnace was invented by Dr. 
Schonherr, of the Badische Anilin 
und Soda Fabrik, of Germany. 
As installed at Christiansand, it 
consists of a long iron tube fixed 
* vertically, through the centre of 
which an arc 16 ft. long is main- 
tained. Alternating current at 
4200 volts, fifty periods, is used, 
and each furnace takes 600 horse- 
Fic. 3.—The Schonherr power. Air blown through this 
furs for fixation of tube with a whirling motion keeps 
Pear the are in the centre. The elec- 
trode at the bottom consists of an 
iron rod which passes through a copper water-cooled 
tube. The iron rod is pushed upwards, as it burns 
away to ferric-oxide, and fresh rods are screwed on as 
required, so that the process does not stop. At the top 
of the tube there is the water-cooler, and it is inside 
here that the are ends by striking across from the 
centre to the side of the tube. 
As will be seen from the arrows in Fig. 3, the in- 
coming air passes through annular tubes, on each 
side of which there are the hot gases from the 
furnace. The air is thus heated to about 500° C. 
before it reaches the arc. After passing through the 
arc, where some of it is heated to about 3000° C., 
it reaches the water-cooler, where its temperature is 
then suddenly reduced. At this point there is a 
rapid mixing of the highly heated nitric oxide next 
to the arc with the cooler air that is whirling past, 
NO. 2227, VOL. 89] 
oxide and air leave the top of the cooler at about 
1200° C. 
The plant at Christiansand is entirely occupied in 
making sodium nitrite for the production of aniline 
dyes, &c. Previously, sodium nitrite had been made 
by the reduction of Chile nitrate with lead, but this 
method of production has now practically ceased. 
Calcium Nitrate. 
As carried out at Notodden, the method of making 
calcium nitrate is as follows:—The nitric oxide gas 
and air pass from each furnace into two fireproof- 
lined gas-collecting pipes, about 6 ft. in diameter, 
lined with fire-brick. These pipes convey the gas to 
four steam boilers, the heat given off by the gases 
being used to raise steam for concentrating the pro- 
ducts and for driving the air compressors for pump- 
ing acids, soda, &c. The gases then go through 
tubes in the evaporating tanks, after which the 
temperature is down to about 250° C. The tempera- 
ture is lowered still further, to 50° C., by passing 
it through a number of aluminium tubes over which 
cold water is flowing. The gas then enters the 
oxidation tanks, which are large vertical iron 
cylinders having acid-proof linings. Here it con- 
tinues to take up oxygen to form nitrogen peroxide, 
the percentages being now about 098 air and 2 
nitrogen peroxide. 
The nitrogen peroxide is brought into contact with 
water to form nitric acid in two series of four towers. 
These towers are built of granite and are filled with 
broken quartz, this substance and the granite being 
chosen because they are not affected by acid. Each 
tower measures 2 metres square by to metres high, 
and it has been found that they will give an absorp- 
tion of 3-3 kilograms of nitric acid per cubic metre 
of space per twenty-four hours. 
When the liquid reaches the bottom of the first 
tower it contains about 4o per cent. nitric acid. 
Recently some very remarkable results have been 
obtained by improving the material with which these 
towers are filled. By using special forms of earthen- 
ware instead of quartz, the towers can be reduced in 
size considerably, and as the cost of the towers is 
usually about four times the cost of the filling 
material, this means much cheaper towers. 
The nitric acid of 40 per cent. solution is sprayed 
on to calcium carbonate, and the carbon dioxide gas 
is driven off, leaving calcium nitrate, 
2HNO, + CaCO,=CO, + H,0 + Ca(NO,),. 
The solution is then pumped into solidification 
pans, under which cold air is circulated to accelerate 
cooling, and the nitrate of lime stiffens into a brittle, 
crystalline mass. This is broken up into pieces 
suited for ball crushing-mills, where they are reduced 
to a granular state. The coarse powder is then raised 
by an elevator into a hopper, from the bottom of 
which it falls into barrels which hold 2 cwt. These 
barrels are lined with paper to guard against damp. 
With the Birkeland-Eyde process, one kw.-year 
gives 500 to 550 kilograms of nitric acid, or 853 to 
938 kilograms of nitrate of lime. The latter usually 
contains 13 per cent. of nitrogen, which corresponds 
to 111 to 122 kilograms of combined nitrogen. It is 
guaranteed to contain 12$ per cent. of nitrogen. 
The best result at Notodden has been goo kilo- 
grams of nitric acid per kw.-year measured at the 
are terminals and allowing for 100 per cent. nitric 
acid. 
The percentages of nitrogen and approximate com- 
parative prices of the various artificial manures are 
| about as follows :— : 
