urbaf2

494 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

with metals, since in the molten state it forms picrates which may initiate explosion.

This depends largely on the metal: lead, iron, copper should be considered as par-

ticularly dangerous.

It was unexpected to find that picric acid does not decompose when exposed

to sunlight. Ciamician and Silber [59] found that an alcoholic solution of picric

acid when exposed to sun rays for many months does not show any change in

its properties. The fact that picric acid turns slightly yellowish when exposed to

light may be ascribed, according to Stepanov [60], to the formation of traces of

ammonium picrate on the irradiated area.

EXPLOSIVE PROPERTIES

Picric acid decomposes according to the equation (Kast [40]):

16C 6 H 3 O(NO 2 ) 3 = 32CO 2 + 40CO + 4CH 4 + 2H 2 O + 3C 2 H 2 + 3HCN +

+ 4.5H 2 + 21.5N 2 + 2NH 4 HCO 3 + 9C (10)

Its heat of explosion is 1000 kcal/kg, the volume of gases produced Ve = 675 l./kg

and temperature t = 3230°C.

Schmidt [61] has derived a number of equations for the decomposition of picric

acid at various densities. For example, at ∆ = 1.39 the equation derived for 1000 g

(i.e. 4.36 moles) of the substance is:

4.36C 6 H 3 O(NO 2 ) 3 = 6.14CO 2 + 14.37CO + 3.94H 2 O + 1.33H 2 O + 0.16CH 4 +

• 0.07CmHn + 0.15HCN + 0.54NH 3 + 6.12N 2 + 5.1C (11)

The heat of explosion = 960 kcal/kg, the volume of gases V 0 = 737 l./kg, t
= 3530°C.
R. Robertson and Garner [62] found the heat of explosion to be 910-935 kcal/kg,

and the volume of gases V. = 725 l./kg.

The impact sensitivity of picric acid is higher than that of TNT. In many coun-

tries the value of 100 has been taken for the sensitiveness of picric acid, sensitiveness

of other explosives being expressed in terms of that of picric acid. Thus the

value for tetryl will be 70 and that for TNT - 115-275, according to various
authors.
The sensitiveness of picric acid to friction is low, but slightly higher than that
of TNT.
The expansion produced in the lead block, as reported by various authors is

250-350 ml. Taking the value for TNT as 100, that for picric acid will be 102-120.
In the mortar test picric acid gives a value of 110-120, and in the sand test 104,
relative to TNT = 100.
The rate of detonation of picric acid, as measured by various workers, is given

in round numbers in Table 116.