NATURE [APRIL 9, 1932 Having for Comparison a Standard Benzene Bulb

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546 NATURE [APRIL 9, 1932 having for comparison a standard benzene bulb. filter transmitting 250-280 p.p. was used in these ex• The powder was then melted, and recrystallised by periments. The effect was shown to have its origin heating the bulb in an electric heater to about 270° C. in the phosphine molecule, but in view of the fact and very slowly cooling it. After noting the defl.exion that phosphine itself does not absorb in the region due to the bulb with the resolidified bismuth, that of 250-280 p.p., it would seem that the incidental presence the container alone was determined by breaking it of mercury vapour resulted in the phosphine being open and dissolving out the metal with nitric acid. decomposed by excited mercury atoms into hydrogen Experiments with similar bulbs and bismuth regulus atoms and probably PH or PH2 radicals, which pro• showed no change of defl.exion after heat treatment. duce the Hinshelwood-Clusius effect. Hinshelwood But when bismuth powder was melted and recrystal• and Clusius concluded that the active material was lised, the diamagnetic susceptibility rose nearly to the present in the gas phase, but on repeating their ex• regulus value. Many samples of colloidal bismuth periment by exposing the mixture in one tube and gave similar results. determining the explosion pressure immediately after These observations indicate that the fall in the in another similar tube, the effect was not observed. susceptibility value with reduction of particle size in That is, the effect is most probably a wall phenomenon, the case of bismuth is a genuine effect. Full details the illumination of the mixture producing a molecule of this investigation will be published elsewhere. or radical which is afterwards adsorbed on the walls ; S. RAMACHANDRA RAO. the latter are thereby enabled to reflect the chains more Annamalai University, efficiently, thus decreasing the explosion pressure. Annamalainagar, Jan. 28. It has also been found that pretreatment of the walls 1 Ind. J. Phys. 5, 559 ; 1930. with atomic hydrogen results in a decreased explosion ' Ind. Chern. Soc., 7, 975; 1930. pressure. H. W. MELVlLLE. ' Ind. J. Phys., 6, 241 ; 1931. Chemistry Department, The University, Edinburgh, Feb. 25. Photochemical Decomposition of Phosphine 1 Sitzungsber. Preuss. Akad., p. 746; 1911. IT is rather surprisipg to find that, although the ' Cf. Dalton and Hinshelwood, Proc. Roy. Soc., A, 125, 294; 1929. photochemistry of ammonia has attracted consider• ' Proc. Roy. Soc., A, 129, 589; 1930. able attention since Warburg's 1 work, no corre• sponding experiments have been carried out with the Structure of the Third Positive Group of equally simple molecule of phosphine. Such experi• CO Bands ments have now been in progress in this laboratory THE third positive group of CO bands has been for some time. studied often before, but no satisfactory analysis of The absorption spectrum of phosphine consists of a the bands seems to have resulted from it. Therefore region of continuous absorption beginning at about we have photographed the bands in the second and 220 p.p. and continuing to 185 p.p., the limit of the spectro• third order of a 21-ft. concave grating with 20,000 lines graph used. Preceding this continuous band there per inch. So far, we have studied the bands ().....+0 to are three diffuse bands in the region 220-230 p.p.. No ().....+4with heads at 2833,2977,3134,3305, and 3493A. fine structure is exhibited by these bands. The The bands are due to a transition. The triplet spectrum, like that of ammonia, would appear to be separation of the state is unnoticeable for J <20. of the predissociation type. Under these conditions we must expect 15 branches Light from zinc or aluminium sparks readily de• if the resultant spin is not yet completely coupled to composes the phosphine into hydrogen and phos• the rotational axis (transition from case a to case b). phorus, which is deposited as the red variety on the We found 13 of these branches arid traces of the walls of the insolation tube. The experiments on remaining two, which are too faint to be observed the direct photochemical decomposition have not yet among the strong main branches. The five heads been completed. The mercury photosensitised re• which are characteristic for the bands under low dis• action has, however, been investigated in some detail. persion are the heads of the 0 3, 0 2, P 3, P 2, and P 1 The rate of decomposition is about ten times that of branches (in the simplified notation of case b). The ammonia under the same conditions. It is dependent initial level shows very strong perturbations from on the diameter of the reaction tube ; for, as the about K = 16 on, and slight irregularities also for very diameter is decreased-that is, the surface volume small K values. This fact makes an analysis of the ratio increased-there is a decrease in the rate of de• higher lines of the bands much more difficult, and composition. For example, in tubes of 2 em., I em., we have not yet completed this part entirely. The and 0·5 em. diameter, the rates are in the ratio moment of inertia for the final state is 16·5 x 10·40, 2·5: 1·5: I. This would indicate that recombination of and for the initial state approximately 14·3 x 10·40, the products of dissociation occurs at the walls of the The character of the A.-doubling and the number of reaction tube. Argon has no effect on the velocity. missing lines near the origin identifies the final elec• On the other hand, oxygen increases the rate of de• tronic state as a regular 3II state. composition as much as five times (PPH, = 0·05 mm. ; Our results are not in agreement with the analysis p 0 , = 0·05 mm)., while the subsequent addition of of Asundi,l who classified these bands as transi• argon (0·1 mm.) still further increases this rate. tions. The fact, however, that the observed structure These observations are most plausibly explained if agrees perfectly with the theoretical expectation that it is assumed that oxygen attacks the products of practically all lines in the region investigated can be dissociation, thus preventing their recombination. arranged into those branches, that all combination The resulting oxide molecules then initiate a stable relations are fulfilled within the limits of experimental chain reaction between the undecomposed phosphine errors, and that the perturbations of equivalent lines and the oxygen.2 are identical in the sixty branches in which they occur, These results partly explain an interesting observa• seems to us a strong argument in favour of the correct• tion of Hinshelwood and Clusius,a who found that on ness of our analysis. Complete details will be found elsewhere. illuminating a PH3 - 0 2 mixture below the lower critical explosion pressure, the pressure to which the G. H. DIEKE. mixture had to be compressed in order to obtain J. W. MAUCHLY. explosion was lower than that of the unilluminated The Johns Hopkins University, Jan. 21. gases. A mercury lamp with a chlorine-bromine 1 Proc. Roy. Soc., A, 125, 277 ; 1929. No. 3258, VoL. 129]