NITRIC OXIDE ' 7
stantially complete, the velocity of the air current being
greater than that of the flame gases. The flame is preferably
spread out so as to form a larger surface.
In order to obtain a higher yield of nitric oxide, many pro-
cesses have been described for heating the nitrogen and oxygen
together under high pressures. One method of carrying this
out is by utilizing explosion pressures.
Hausser x explodes coal gas and air under pressure, and
maintains the explosion pressure as long as possible. The
products contain in this case 1-3-1-7 per cent, of nitric oxide.
Haber 2 states that when a flame is burnt under 8-10 atmo-
spheres pressure, oxides of nitrogen are produced, and a 10
per cent, solution of nitric acid may be obtained by burning
hydrogen in an equimolecular mixture of oxygen and nitrogen.
The question of the production of oxides of nitrogen in
explosions in which excess of air is present is discussed by
Dobbelstein,3 and in particular the use of coke oven gas for
this purpose.
Using an illuminating gas of the following composition,
H2 ^44% * Na=l%
CH4 =25% 02 -8%
CO = 14% Unsatd. hydrocarbons = 4%
C02 ^3%
he obtained a yield of 125 grams of nitric acid per cub. metre
at 5 atmos. pressure.
Increase in the yield of nitric oxide can be effected in two
ways :—
(a) By increase in pressure.
(b) By increase in the proportion of oxygen up to the theo-
retical value required for nitric oxide.
The oxidation of nitrogen has also been successfully
attempted by the use of catalysts, e.g. the calcined oxides
of such metals as cobalt, chromium, nickel, platinum, palla-
dium, barium, magnesium, lead, etc.
The action of the electric arc, hot flames, etc., is usually
considered to be purely thermal, but Warburg4 and others
1 Fr. Pat. 420,112, 1910; J. Soc. Chem. Ind., 1911, 30, 360.
2 Zeitsch. angew. Chem., 1910, 23, 684.
3 Stahl u. Eisen, 1912, 32, 1571; J. Soc. Chem. Ind., 1912, 31, 981.
4 Zeitsch. Mektrochem., 1906, 12, 540.