urbaf2

OTHER NITRO DERIVATIVES OF PHENOLS^525

the properties of its potassium salt (as for example the solubility) differ from those

of potassium picrate.

The investigations of the above authors were checked by Desvergnes [3], who

found the melting point of “isopicric acid” to be 119.7°C. Moreover, he was

able to observe that picryl chloride, on boiling in water, alcohol or pyridine also

gives a certain quantity of “isopicric acid”, according to the equation:

(2)

The evidence for the existence of “isopicric acid” is not convincing.

PICRIC ACID SALTS

Metal salts of picric acid may be formed by the action of picric acid on metals,

their oxides or carbonates and in certain cases also on their other salts. They are

crystalline substances, mostly more sensitive to friction, impact and heat, than

picric acid itself. Due to their high sensitivity to stimuli, the explosive properties

of picrates were known long before those of picric acid.

Picrates formed by precipitation from aqueous solutions contain water of crys-

tallization which may desensitize them. For example, the decahydrate of ferric

picrate shows no sensitiveness to friction and impact and cannot be ignited when

in direct contact with a flame, whereas the anhydrous compound is exceptionally

sensitive to these stimuli.

The properties of picrates have been examined by several authors, e.g. Cheltsov

[4], Will [5], Silberrad and Phillips [6], Kast [7], Krauz and Turek [8], Tucholski [9]

and T. Urbanski and Slon [10].

Tucholski determined the dehydration temperatures of picric acid salts hydrates,

their melting points, initiation temperatures and temperatures preceding explosion.

T. Urbanski and Slon determined their sensitiveness to impact and flame.
The results obtained by the above authors are presented in Table 119.
All picrates, especially lead, barium, calcium, iron and nickel picrates, should
be considered as highly undesirable in picric acid. They have caused a great number
of accidents. Among them only potassium picrate has found some practical uses,

viz. in some high explosive and propellant compositions no longer in use at the

present time.

Nowadays the only picrates applied as explosives for military purposes are
ammonium and lead picrates, the latter being an initiating explosive (Vol. III).