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The preparation of tree radicals from lead tetraethyl and tetramethyl has been described by Paneth and Hofeditz* and, having fully confirmed their work with the former compounds we sought, at the commencement of this investigation, to apply a simi1ar technique to an analogous problem : the preparation of atomic hydrogen by the thermal dissociation of metallic hydrides. preliminary experiments on the dissociation of certain of the more accessible hydrides showed, however, that those of sulphur, selenium, tellurium, arsenic, antimony and tin, under the conditions employed, failed to yield hydrogen which was capable of removing even the most sensitive metallic mirror—such a mirror, we had been able to show, disappears quickly and completely when atomic hydrogen is present. It is really not surprising that the hydrogen from these compounds is inactive since the accepted accommodation coefficients of the elements involved are relatively low. In this respect, the hydrides of lead and bismuth promised greater success. Hitherto, the hydrides of lead and bismuth have been obtained only in minute quantities, and have been characterized entirely by circumstantial evidence, hence it was necessary to discover means whereby they might be prepared on a larger scale. Bismuth hydride, as it proved, did not present much difficulty ; the yields from the dissolution of a magnesium-bismuth alloy in acid, although email, sufficed for our purposes. On the other hand, the results accruing from the whole of our work on the lead compound are so meagre, and so dependent on inexplicable circumstances, as to leave a sense of uncertainty regarding the nature of the traces of lead-carrying body produced in the operations, Neither the dissolution of the magnesium alloy, nor the reduction of lead salts by magnesium gave the hydride, whilst a change of the alloying metal to lithium, the use of which in these preparations is new, resulted in the merest trace of a very impure, volatile lead compound from 20 gm. of the alloy, and was without promise of yielding either a pure product or a sufficient quantity. About fifty experiments with the oscillating are, sometimes in its original form* and sometimes, modified so as to reduce the by products contaminating the lead-containing condensate, agreed down to the minutest detail with the recorded observations of Paneth and Norring, but, incidentally, gave uselessly small fields, they found the presence of carbon to be a condition essential to the appearance of lead in the effluent gases, and of this there can be no question. That our lithium contained carbon, whereas our magnesium was practically free from it is also significant in this connection.

THE formation of unimolecular films on solid surfaces has been demonstrated by Langmuir1 for gases and by Carver2 for toluene, but others employing different materials have obtained results interpreted as indicating an adsorbed layer of multi-molecular character. At the moment the position is such that “definite agreement about the validity of direct experimental evidence is hardly reached”3 and for this reason it may be of value to record the discovery of two unimolecular films made during our most recent work on the combination of hydrogen with sulphur in Pyrex glass. For the first time, so far as we are aware, this reaction has now been studied at low hydrogen pressures of the order of 3 mm. at the temperature employed, namely, 343° C. In the light of previous experience5, the most rigid precautions were taken to ensure the absence of oxygen or moisture from the reactants.

BODENSTEIN1 studied this reaction in sealed bulbs containing excess of sulphur, and found a temperature coefficient of 1.34 between 234° and 283°, and 1.77 between 310° and 356°. His work was criticised, by Norrish and Rideal2, as possibly vitiated by the hydrogen sulphide liberated on the solidification of the residual sulphur, and as leaving uncertain, in view of the variable temperature coefficient, the part played by the walls of the bulbs. These workers employed a dynamic method, and showed that the logarithms of the total reaction velocity—always, however, measured in the presence of nitrogen—when plotted against absolute temperature yielded a curved line. The differences in the velocities obtained, using hydrogen at partial pressures of O.810 atm. and 0.304 atm., respectively, when suitably plotted gave a straight line which was interpreted as belonging to the gaseous reaction alone, since the surface reaction, common to each series, was assumed, and reasonably so, to be independent of pressure. The velocity of the composite reaction was also shown experimentally to be increased by increasing the glass surface, to which it was stated to be proportional; and to be independent of the amount of sulphur present. Knowing the contribution of the gaseous reaction, data for the surface were deduced, and thus the temperature coefficient of each reaction was obtained: homogeneous 2.19, heterogeneous 1.48.

WE are able to report the isolation of copper carbonyl, which we obtained from the reaction of carbon monoxide with heated cuprous oxide. It is a white, readily sublimable solid, the vapour of which is dissociated at a higher temperature with the consequent deposition of metallic copper. Only small quantities are formed, but enough has been collected to afford a preliminary analysis indicating Cu(CO)3 as the empirical formula. A polymeric form would be expected in the case of copper, and its properties suggest that it is very possibly dimeric.

RECENTLY1 we described a volatile compound, traces of which were formed when a variety of specimens of cuprous oxide were heated in carbon monoxide, as a carbonyl of copper. Further experiments have shown that the phenomena observed resulted from adventitious halide present in the oxides used.

IN the course of an investigation of the oxides of rhenium in progress in these laboratories, we have sought to repeat the preparation of the highest oxide described by I. and W. Noddack,1 Re2O8, which was obtained by them on heating the heptoxide below 150° in a stream of oxygen. The yellow heptoxide used in the Noddacks' preparations melted at 220° and gave rise to a white sublimate at 150° described as Re2O8 and possessing the property of decolorising acidified potassium permanganate. The melting point of our specimens of heptoxide has invariably been about 300°,2 and this material failed to give any evidence of a white sublimate when heated in a stream of oxygen to temperatures below its melting point. Moreover, quantitative experiments repeatedly showed that its formation was unattended by any increase in weight. The sublimate was identical in crystalline form with the heptoxide, was decidedly yellow, and melted to a yellow solid, also indistinguishable from the heptoxide.