IV. On the action of electricity on gases.—II. On the electric decomposition of carbonic-acid gas

Abstract

At a very early period of the investigation on the action of electricity upon oxygen, which formed the subject of my previous memoir, the idea occurred to me that although but a small and limited proportion of the total oxygen passed through the induction-tube was converted into ozone (which proportion could not be exceeded by any modification I had been able to effect in the conditions of the experiment), it might be practicable to replace that portion of the oxygen which was unaffected by the action of electricity by an indifferent gas, and thus effect the total conversion of oxygen into ozone, or even the actual isolation of the ozone by the subsequent removal of the gas by which it was diluted. Thus, for example, by the passage of 100 cub. centims. of oxygen through the induction-tube, a gas can readily be obtained of which the iodinetitre is 5 cub. centims. This corresponds, according to my previous experiments, to an absorption by hyposulphite of soda of 10 cub. centims. of a gas containing in that space the matter of 15 cub. centims. of oxygen. If, therefore, we were to mix 15 cub. centims. of oxygen with 85 cub. centims. of an indifferent gas which should be unaffected by the action of the electricity, and pass the mixed gases through the induction-tube (assuming the same proportion of ozone to be still formed as in the case of the passage through the tube of pure oxygen), the total amount of oxygen in the gas would be con­verted into ozone, and be removed in that form by passing the gas though a solution of hyposulphite of soda. With the view of testing this idea by a critical experiment, I passed such a mixture of carbonic-acid gas and oxygen through the induction-tube. The formation of ozone was at once apparent, and was rendered evident by the action of the gas issuing from the induction-tube upon a neutral solution of iodide of potassium. But on examining the composition of the gas I soon discovered that the proportion of oxygen in it had actually increased, owing to the decomposition in the induction-tube of the carbonic-acid gas into oxygen and carbonic oxide. I did not publish this experiment; but the apparatus by which it was effected long stood upon my laboratory table, and, together with the results, has repeatedly been explained by me to other chemists. Since that time, as appears from the pages of the 'Comptes Rendus,’ this decomposition of carbonic-acid gas under the influence of electricity has been cited as a novel discovery. So far as the bare fact of the decomposition of carbonic-acid gas, under the influence of electricity, in the induction-tube into oxygen and carbonic oxide is concerned, the results of this experiment might, even at the time it was made by me, have reasonably been anticipated, not only from the circumstance that carbonic-acid gas is, as is well known, decomposed by the passage of the electric spark, but also that Plücker had already observed (although I was unaware of the observation) that when the electric discharge was passed through rarefied carbonic-acid gas, the spectrum of the gas after a short time changed into the spectrum of carbonic oxide, and from this circumstance had inferred the decomposition of the gas. But the observations of this eminent investigator were made under very different circumstances to mine; and he was not cognizant of the forma­tion of ozone, which was the critical point of my experiment, and a result which could not have been ascertained by his method of observation. The experiment having failed in its immediate object was for a time laid aside by me. Subsequently, however, I reverted to it under a somewhat modified form. It occurred to me, instead of mixing oxygen with carbonic acid, to endeavour to generate in the very atmosphere of the carbonic acid itself, by the electric decomposition of the gas, the requisite amount of oxygen. I passed, therefore, pure and dry carbonic acid through the induction-tube, and examined the gases resulting from its decomposition, estimating the ozone by the titre of the gas, and also the oxygen and carbonic oxide formed. This examination at once convinced me of the importance of the experiment in reference to the problem of the isolation of ozone, and became the foundation of the following research, which has gradually been extended in more than one direction.