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510 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

cement and are reinforced from outside by tarred sheet iron tightened by hoops.

The top of the nitrator is partly covered by a Volvic plate equipped with a pipe

connected with the ventilating duct (1). An aluminium plate (2) covers the rest

of the nitrator top.
In the nitrator described batches of 100-150 kg of phenol may be nitrated:

The whole nitration unit is shown in Fig. 116. Nitrators (1) are connected with pro-

portioning tanks for sulphophenol and nitrating acid. Vapours evolving during

the nitration flow to jars (3), (4) and (5), passing on their way through the cooling

coil (6). Here nitric and nitrous acids are condensed. Non-condensed nitrogen oxides

pass to the absorption tower (7), sprayed with water and supplied with air for oxi-

dation. Here the oxides are converted into nitric acid.

FIG. 116. Flow sheet of the nitration of sulphophenol to picric acid

(Pascal [2]).

Next to the nitrator is a wooden double-bottomed tank (8) (the diameter of its

upper parts is 1.15 m, height 1.0 m) for separating picric acid from spent acid and

for washing the product with water. A narrow gauge railway (9) operates for two

lines of nitrators located symmetrically on both its sides.

Similar cylindrical nitrators were in use in Great Britain (Fig. 117).
According to British data, the consumption of raw material for 1 ton of picric
acid is:
British method French method
Phenol 540 kg 538 kg
NaNO 3 1990 kg* 1870 kg
H 2 SO 4 2930 kg 2620 kg

• The nitric acid recovered in absorbers from nitrogen dioxide generated in the nitration process, has not been
  taken into account here. Usually 160 kg of HNO 3 (100%) per 1 ton of picric acid em be recovered.

United States method

During World War I a method of manufacture of picric acid was established

in the United States.

Olsen and Goldstein [6] described the method as follows.

302.2 kg of phenol are sulphonated with 605 kg 93% sulphuric atid at 95-

98°C during 6 hr. The product is composed of 80% phenol-4-sulphonic acid and
20% phenol-2,4-disulphonic acid.