In the course of a specific heat investigation at the National Physical Laboratory the need arose for an accurate knowledge of the heat of formation of nitrous oxide and since the published values of this constant differed widely it was decided to make a new determination.The work was undertaken by both the Physics and Engineering Departments of the National Physical Laboratory, and, whereas the former used a con tinuous flame method* involving combustion at constant pressure, the latter adopted the explosion method and a constant volume reaction.I t is the purpose of this paper to give an account of the results obtained by the explosion method.The mode of attack is already familiar and consisted, in this investigation, in exploding mixtures of the approximate composition 3C0 -j-2N20 and 3CO -j-0 2 and ascribing the difference in their heats of reaction to the splitting up of the 2NaO into 2N2 and 0 2. Subsequently a series of experiments was made on the mixture 3H2 -(-2N20 and its heat of reaction was compared with th at of the calibration mixture 3H 2 + 0 2. The result confirmed the value already obtained from the CO experiments.A reference has just been made to the calibration mixture and it should be pointed out at once th at the heat capacity of the calorimeter was determined by exploding 3H2 -f-0 2 mixtures in it, and hence the values given for the heats of formation of N 20 and C 0 2 are based on the heat of formation of H 20 (liquid) which has been taken as 68,320 gm. cal.i3° a t constant pressure and at 25° C.The accuracy with which the required heat of formation can be determined depends on the precision with which measurements can be made of the masses of the gases taking part in the reaction and the quantities of heat evolved. For the measurement of the latter the bomb calorimeter shown in fig.
For many years work has been in progress in the Engineering Department of the National Physical Laboratory on problems involving the explosion of gaseous mixtures in a closed vessel or bomb (Fenning 1924, 1925, 1926; Fenning and Tizard 1927). The experience gained and the technique developed were considered to warrant a new attack being made on the measurement of the specific heats of gases at high temperatures, particularly of those gases which comprise the working substance of the internal combustion engine. The work was therefore put in hand and carried out for the Department of Scientific and Industrial Research. At the time the investigation was started a considerable amount of data, based on explosion experiments, was available, and this was being supplemented by values of the specific heat obtained from the analysis of the band spectra of the gases concerned. Activity in this latter field has continued and values are now available for a considerable number of gases over a wide temperature range as will be seen from a summary by Lewis and von Elbe (1935
a
) published about three years ago.
During the past five years a programme of research involving air-fuel explosions in a closed vessel has been in progress at the National Physical Laboratory for the Engineering Research Board of the Department of Scientific and Industrial Research. Among the experimental results obtained, those relating to Carbon Monoxide and Methane were considered likely to be of interest to the Society, and form the subject of the present communication.Of the two investigations described, the first gives experimental data on the respective influences of hydrogen-air and water vapour on a carbon monoxide-air explosion, and the second relates to explosions of methane and air over a comparatively wide range of initial temperature and pressure.Part I.-Carbon Monoxide-Air E xplosions in a Closed Vessel, with SpecialReference to the E ffect of Additions of (a) H ydrogen-Air and ( ) Water Vapour.When Bone and H award published their interesting experiments* showing, inter alia, the marked influence of a small proportion of H 2-air on a CO-air explosion at an initial pressure of 50 atmospheres and at atmospheric initial temperature, it was suggested by the Engine Sub-Committee of the Aeronautical Research Committee th at a similar series of experiments, at initial pressures corresponding to engine con ditions, should be put in hand at the National Physical Laboratory. Mr. H. T. Tizard made the further suggestion that, at the same time, the effect of water vapour additions to a CO-air mixture should be investigated.In carrying out these suggestions three series of explosions were performed at an initial pressure of 76-8 lbs. per square inch (absolute), and at an initial temperature of 50° C., a pressure-time record being obtained of each explosion.The mixtures in the respective series were :-2 (mH2 -f-wCO) -j-0 2 -j-3*8N2, where m and n are variable, but + n = 1 ; water vapour content less than 1 in 2000.
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