160 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVESacid layer is transferred to a special tank while that of the product goes to another
tank (for example direct for washing if it is an end product, or to another nitrator
if it is to be nitrated further). To make practicable the transport of the two layers
to different locations the discharge pipe should be equipped with a sight glass,
through which the partition boundary of the phases can be seen.
An advantage of discharge by means of compressed air is that the whole plant
can be located in a low building. If the nitrator is emptied through an outlet in
its base a high building is necessary. This is of particular importance when under-
ground plant is to be constructed, for the cost rises considerably as the depth in-
FIG. 34. Flow diagram, nitration, the discharge of the nitrator through
the bottom: 1 - nitrator; 2 - separator; 3 - pressure-egg.creases. A drawback associated with the use of compressed air for discharging the
nitrator contents is the risk of damage and the operatives being burned consequent
on breakage of the sight glass.
Discharging the nitrator through an outlet has the further drawback that it
makes the reactor more difficult to construct.
In the case of substances that solidify (for example, TNT) all pipes and valves
should be provided with heating jackets. If the nitration product solidifies at a