108 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



was decomposed by the electric current, and precisely the same quantity of hydrogen 

 set free at the cathodes of the three solutions. 



808. The experiment was made thus. Portions of the dilute sulphuric acid were 

 put into three basins. Three volta-electrometer tubes, of the form figg. 5, 7- were filled 

 with the same acid, and one inverted in each basin (707.)- A zinc plate, connected 

 with the positive end of a voltaic battery, was dipped into the first basin, forming" the 

 positive electrode there, the hydrogen, which was abundantly evolved from it by the 

 direct action of the acid, being allowed to escape. A copper plate, which dipped into 

 the acid of the second basin, was connected with the negative electrode of the Jirst 

 basin ; and a platina plate, which dipped into the acid of the third basin, was con- 

 nected with the negative electrode of the second basin. The negative electrode of the 

 third basin was connected with a volta-electrometer (711-)j and that with the nega- 

 tive end of the voltaic battery. 



809. Immediately that the circuit was complete, the electro-chemical action com- 

 menced in all the vessels. The hydrogen still rose in, apparently, undiminished 

 quantities from the positive zinc electrode in the first basin. No oxygen was evolved 

 at the positive copper electrode in the second basin, but a sulphate of copper was 

 formed there ; whilst in the third basin the positive platina electrode evolved pure 

 oxygen gas, and was itself unaffected. But in all the basins the hydrogen liberated 

 at the negative platina electrodes was the same in quantity, and the same with the 

 volume of hydrogen evolved in the volta-electrometer, showing that in all the vessels 

 the current had decomposed an equal quantity of water. In this trying case, there- 

 fore, the chemical action of electricity proved to be perfectly definite. 



810. A similar experiment was made with muriatic acid diluted with its bulk of 

 water. The three positive electrodes were zinc, silver, and platina ; the first being 

 able to separate and combine with the chlorine without the aid of the current ; the 

 second combining with the chlorine only after the current had set it free ; and the 

 third rejecting almost the whole of it. The three negative electrodes were, as before, 

 platina plates fixed within glass tubes. In this experiment, as in the former, the 

 quantity of hydrogen evolved at the cathodes was the same for all, and the same as 

 the hydrogen evolved in the volta-electrometer. I have already given my reasons for 

 believing that in these experiments it is the muriatic acid which is directly decomposed 

 by the electricity (764.) ; and the results prove that the quantities so decomposed are 

 'perfectly definite and proportionate to the quantity of electricity which has passed. 



811. In this experiment the chloride of silver formed in the second basin retarded 

 the passage of the current of electricity, by virtue of the law of conduction before 

 described (394.), so that it had to be cleaned off four or five times during the course 

 of the experiment ; but this caused no difference between the results of that vessel 

 and the others. 



812. Charcoal was used as the positive electrode in both salphuric and muriatic acids 

 (808. 810.) ; but this change produced no variation of the results. A zinc positive 



