1 76 Dr. Faraday's Experimental Researches in Electricity. 



fore in contact with the fluid by a much smaller surface, and 

 for a much shorter time than those at the plates; hence less 

 solution and a greater collection. 



719. There was also another effect produced, especially by 

 the use of large electrodes, which was both a consequence 

 and a proof of the solution of part of the gas evolved there. 

 The collected gas, when examined, was found to contain small 

 portions of nitrogen. This I attribute to the presence of air 

 dissolved in the acid used for decomposition. It is a well- 

 known fact, that when bubbles of a gas but slightly soluble in 

 water or solutions pass through them, the portion of this gas 

 which is dissolved displaces a portion of that previously in 

 union with the liquid: and so, in the decompositions under 

 consideration, as the oxygen dissolves, it displaces a part of 

 the air, or at least of the nitrogen, previously united to the 

 acid ; and this proceeds most extensively with large plates, be- 

 cause the gas evolved at them is in the most favourable condi- 

 tion for solution. 



720. With the intention of avoiding this solubility of the 

 gases as much as possible, I arranged the decomposing plates 

 in a vertical position (707. 708.), that the bubbles might 

 quickly escape upwards, and that the downward currents in 

 the fluid should not meet ascending currents of gas. This 

 precaution I found to assist greatly in producing constant re- 

 sults, and especially in experiments to be hereafter referred 

 to, in which other liquids than dilute sulphuric acid, as for in- 

 stance solution of potash, were used. 



721. The irregularities in the indications of the measurer 

 proposed, arising from the solubility just referred to, are but 

 small, and may be very nearly corrected by comparing the 

 results of two or three experiments. They may also be al- 

 most entirely avoided by selecting that solution which is found 

 to favour them in the least degree (728.) ; and still further un- 

 collecting the hydrogen only, and using that as the indicating- 

 gas ; for being much less soluble than oxygen, being evolved 

 with twice the rapidity and in larger bubbles (717.), it can be 

 collected more perfectly and in greater purity. 



722. From the foregoing and many other experiments, it 

 results that variation in the size of the electrodes causes no va- 

 riation in the chemical action of a given quantity of electricity 

 upon water. 



723. The next point in regard to which the principle of 

 constant electro-chemical action was tested, was variation of 

 intensity. In the first place, the preceding experiments were 

 repeated, using batteries of an equal number of plates, strongly 

 and weakly charged ; but the results were alike. They were 



