The decomposition of both liquid cyclotrimethylenetrinitramine (cyclonite) and cyclotetramethylenetetranitramine follows the unimolecular equation, the Arrhenius frequency factors being very large. The unimolecular uncatalysed decomposition of cyclonite in dilute solution in dicyclohexyl phthalate and trinitrotoluene has a frequency factor approaching the normal value. A more concentrated solution of cyclonite decomposes faster than the dilute solutions ; this fact and the anomalous frequency factor for the pure liquid are explained in terms of a chain reaction of short length with a temperature dependent chain length. Analyses of the gaseous products are given, which with the kinetic data show trinitrotoluene to behave effectively as an inert solvent with respect to cyclonite.

The decomposition of nitroglycerin and ammonium nitrate follows the unimolecular equation. That of pentaerythritol tetranitrate shows slight autocatalysis and ethylenediamine dinitrate shows considerable autocatalysis. Normal Arrhenius expressions for the decomposition rate were obtained for the two nitrates, but the frequency factor for the two nitric esters is extremely large. With pentaerythritol tetranitrate a significant diminution of the frequency factor in dilute solution was ascribed to reaction chains having a short length dependent on temperature. Analyses of the gaseous products were made including the use of a flow method with pentaerythritol tetranitrate.

The interaction of water with the clean Fe(111) surface and that surface modified by small coverages of Ga has been investigated. Both thermal energy atom scattering and Auger electron spectroscopy have been used to probe this interaction. Water adsorption occurs via a molecular precursor state on these surfaces, and a passivated overlayer is formed on the clean surface exposed to water at 423 K. Small amounts of Ga precoverage, from the decomposition of triethyl gallium, strongly affect the subsequent water adsorption. Preadsorbed gallium reduces the molecular water sticking coefficient and inhibits water dissociation. This effect is proportional to the Ga precoverage. Electron beam irradiation during Auger measurement also strongly affects the water adsorption on the clean and Ga modified surface, and this effect is discussed.

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The instability of z : 4 : 6-trinitrotcluene (TNT.) at high temperatures, as exemplified by its spontaneous explosion, is well known, but few detailed observations of the thermal decomposition and vaporisation preceding the explosion are to be found in the literature. Such data are, however, of some interest in the fundamental study of the thermal sensitiveness of explosives. Experimental.Material.-A commercial TNT., m.p. 80-5O c., containing approximately g g yo of a-TNT, was used for the decomposition and ignition experiments. a-TNT. was prepared from this by repeated recrystallisation from conc. H,SO,.Measurement of Decomposition Rate .-The decomposition preceding explosion was examined in Pyrex glass reaction bulbs, nitrogen, hydrogen or air being present at atmospheric pressure to reduce distillation of the liquid from the hot zone. The methods for rapid heating of the sample of explosive and for recording rapid pressure changes were those described previous1y.l Measurement of Boiling-point .-The induction period before the explosion of TNT. a t its boiling point is sufficiently long (about 20 sec.) t o enable a direct measurement of the b.p. t o be made before the explosion. The sample of TNT. was introduced by an electromagnetic arrangement into a vertical Pyrex tube 1-5 cm. internal diam. immersed to a depth of 2-3 cm. in a bath of fused nitrates maintained a t a temperature usually about 30" c. above that of the boiling point to be measured, and containing air or nitrogen a t the required pressure. The hot junction of a platinum-platinum-rhodium thermocouple was fixed about 3 mm. above the surface of the TNT. to measure the temperature of the condensing vapour. This particular thermocouple has no catalytic effect on the decomposition of TNT. The E.M.F. was measured with a potentiometer and shortperiod galvanometer, the thermocouple being calibrated by direct immersion in a nitrate bath, and the resulting curve checked a t four points by determining the boiling points of benzoic acid, phthalic anhydride, benzophenone and anthracene by the method used with the TNT., the values found being within ri0 c.of the accepted values. The b.p. of benzoic acid was also found a t 12 cm. pressure and a value obtained in close agreement with the vapour pressure 1 Larger quantities than 50 mg. were then required for explosion.