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356 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

nitrators for continuous nitration are as a rule smaller for a given output. More

dangerous reactions are also carried out in nitrators of smaller size.

Cast iron was the material most often used for the construction of nitrators,

and forged sheet iron less so. Now stainless sheet steel is generally used. Stainless

steel sheet must be welded by modern methods (under a hydrogen atmosphere),

since otherwise the seam would be a site relatively easily corroded. Formerly before

reliable methods of welding had been developed, metal sheets were riveted to fabri-

FIG. 29. Diagram of the construction of nitrator.

cate nitrators. In certain cases sheet lead was widely used, e.g. for the nitration

of glycerol. For certain substances easy to nitrate (phenols) earthenware vessels

may be used or iron nitrators with an inner lining of an acid resistant ceramic

material.

HEAT EXCHANGE DEVICES

If a nitrator is equipped only with a cooling or heating jacket, the ratio of the

heat exchange area to the nitrator capacity depends on the latter. When the capa-
city is cubed the surface area is squared. Thus, when the dimensions of a nitrator

are increased, the heat exchange area may no longer be adequate. Then, a
stainless steel coil or a lead coil must be mounted inside the nitrator.

STIRRERS

The influence of stirring on the nitration rate and the safety of the operation

has already been emphasized. It is evident that special attention must be paid to

the stirring equipment provided in a nitrator. Various types of stirrers are used.
Horseshoe stirrers, the shape of which fits well into the inside of a nitrator,

are the simplest type (Fig. 29).