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490 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

sulphuric acid, it absorbed 1.9% of water under the same conditions, while at 0.16%

S0 3 , ca. 5% of water was taken up.

Density. The specific gravity of picric acid is 1.813, and that of molten product

1.589 at 124°C and 1.513 at 170°C. The apparent weight of the crystalline substance

is 0.9-l .0.

The density of pressed picric acid depends on the pressure applied (Dautriche [49]).

Pressure, kg/cm^2 Average density, g/cm^3

275 1.315

685 1.480

1375 1.614

2060 1.672

2750 1.714

3435 1.731

4125 1.740

Kast found the density at 4000 kg/cm^2 to be 1.63 g/cm^3 and at 4500 kg/cm^2

1.74 g/cm^3. In practice, on account of the risk involved, pressures higher than

2000 kg/cm^2 are seldom applied.

Molten picric acid solidifies, when cooled slowly, to a substance of an average

density of 1.66 g/cm^3. On rapid cooling a density of 1.70 g/cm^3 may be attained

(Kast [40)].

THERMOCHEMICAL PROPERTIES

The specific heat of picric acid, as measured by C. A. Taylor and Rinkenbach

[50], is:

Temperature, °C Specific heat, Cal/g

0 0.234

20 0.250

40 0.266

60 0.282

80 0.300

100 0.318

120 0.337

The heat of solidification of picric acid is, according to Gamer and Abemethy

[51], 4.30 Cal/mole. Rinkenbach [52] reported it to be 4.66 Cal/mole.

Heat of combustion and heat of formation of picric acid and of other nitrophenols.

The heat of combustion of picric acid at constant volume (corrected for the nitric

acid formed) is 621.2 kcal/mole and the heat of formation is 63.3 kcal/mole or

276.4 kcal/kg (Gamer and Abemethy [51]).

According to other authors, the heat of formation of picric acid ranges from

46.8-50.9 kcal/mole.

Garner and Abemethy have given the following values for heats of formation

of other nitrophenols:

o- nitrophenol +63.4 kcal/mole

p- nitrophenol +66.3 kcal/mole

2,4-dinitrophenol +69.9 kcal/mole