Discussion

J. C. Cain, F. E. E. Lamplough, F. E. Weston, G. Senter, E. Feilmann, N. T. M. Wilsmore, V. H. Veley
1909 Transactions of the Faraday Society  
regarded the omission of a thermometer in the reacting liquid in Mr. Lamplough's experiments as a very serious error, which lie considered to throw great doubt on the whole of the results recorded by that author. He questioned the value of a blank experiment where temperature was concerned, especially in measuring velocity constants which varied enormously with temperature. The speaker also pointed out that the decomposition of a diazo-salt was an exothermic reaction, aiid in his own
more » ... his own experiments he had always observed that the heat evolved (in the experiments carried out at the higher temperatures) was sufficient to raise the temperature of the solution by 2" or 3O. A consideration of this fact, together with the method recorded by Mr. Lamplough of heating the diazo-solution "one or two degrees higher " than the temperature of the bath might well account for the higher values of the velocity constants obtained. Assuming his own value of the constant in the case of diazobenzene chloride at 50" to be correct, Mr. Lamplough's value would correspond with a temperature of 53.9. Although h h . Lamplough had questioned the riglit of Cain and Nicoll to conclude that their experiments confirmed previous observations on the unimolecular nature of the reaction, he doubted whether better agreeing numbers were to be found in the literature for any other uniinolecular reaction, and an examination of the figures in the " worst" experiments of Cain and Nicoll and of Lamplough showed that the difference between the highest and lowest values was of the same order in each case, Mr. F. E. E. Lamplough said that it was difficult to satisfy the last speaker. Dr. Cain, who had stated that the experimental difficulties due to the high velocities of decomposition of diazo salts had prevented him from working at 67O, criticised the fact that one value of the velocity constant obtained in an experiment at this temperature by the speaker (Proc. Camb. Phil. SOC., 14, 588) was not in close agreement with the other values for the same experiment, whilst in the experiment at the lowest temperature Dr. Cain seemed to imply that manipulation had been resorted to in order to obtain the closely agreeing values given. To such an implication there could be no reply. The speaker had never at any time attributed the continuous regular variations of the velocity constants shown in the work of Cain and Nicoll to experimental error, but to the inherent untrustworthiness of the method. After dealing with the experiniental justification of his method of determining the temperature of the reacting solutions (Zoc. cit., p. 590), Mr. Lamplough briefly described how he had arrived at the values for the degree of supersaturation obtained during his experiments on the decomposition of diazobeiizene chloride. Two experiments had been made in the same vessel, with solutions of the same composition at the same temperature. One esperiment, in which the solution had been thoroughly agitated by stirring to avoid supersaturation, measured the gas actually formed by the reaction. The other experiment without agitation was a measure of the evolution of gas when no precautions had heen taken to prevent its retention. The difference bctwecn the aniounts of gas evolved during a given time was therefore the volunie of gas retained by the liquid in the second experiment. In other experimcnts the still liquid was suddenly agitated at an carly stage, and the retained gas was then given off and mcssured. By these esperiments degrees of saturation up to IOO had been measured. He called particnlar attention to the fact that in the expcrinient wifh agitation of the solution there was no cvidencc of any departure from the uiiimolecular law ;
doi:10.1039/tf9090500010 fatcat:s3higzvwpjepblt6loq6z7w6oa