"The constituents of coal or enriched water gas which give it value as a light producer are known collectively as "illuminants". They consist essentially of ethylene and propylene and in the analysis are determined by means of fuming sulphuric acid. This method of determination is very unsatisfactory as it is impossible to ascertain the relative percentages of the two gases, only the total being found. A series of experiments were made, for the purpose of finding a reagent that could be used for separating the members of the illuminating group and while thus engaged, a solution of iodine in potassium iodide was tried for the extraction of the ethylene. The gas combined comparatively slowly but at a rate which was measurable and which seemed to be proportional to the concentration of the ethylene in the mixture. The description and discussion of the experiments bearing on this velocity of combination, it is the object of this thesis to describe" – leaf .