82 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



according to some relation of the proportionals or equivalents of the elements, could 

 be discovered. The proto compounds only, amongst those just referred to, were de- 

 composable ; and on referring to the substances quoted to illustrate the force and 

 generality of the law of conduction and decomposition which I discovered (402.), it 

 will be found that all the oxides, chlorides, and iodides subject to it, except the chlo- 

 ride of antimony and the periodide of mercury, (to which may now perhaps be added 

 corrosive sublimate,) are also decomposable, whilst many per compounds of the same 

 elements, not subject to the law, were not so (405. 406.). 



680. The substances which appeared to form the strongest exceptions to this ge- 

 geral result were such bodies as the sulphuric, phosphoric, nitric, arsenic, and other 

 acids. 



681. On experimenting with sulphuric acid, I found no reason to believe that it 

 was by itself a conductor of, or decomposable by, electricity, although I had pre- 

 viously been of that opinion (552.). When very strong it is a much worse conductor 

 than if diluted*. If then subjected to the action of a powerful battery, oxygen 

 appears at the anode, or positive electrode, although much is absorbed (728.), and hy- 

 drogen and sulphur appear at the cathode, or negative electrode. Now the hydrogen 

 has with me always been pure, not sulphuretted, and has been deficient in proportion 

 to the sulphur present, so that it is evident that when decomposition occurred water 

 must have been decomposed. I endeavoured to make the experiment with anhydrous 

 sulphuric acid. It appeared to me that in that state, when fused, sulphuric acid was 

 not a conductor, nor decomposed ; but I had not enough of the dry acid in my pos- 

 session to allow me to decide the point satisfactorily. My belief is, that when sul- 

 phur appears by the action of the pile on sulphuric acid, it is the result of a 

 secondary action, and that the acid itself is not electrolyzable (757.)' 



682. Phosphoric acid is, I believe, also in the same condition ; but I have found it 

 impossible to decide the point, because of the difficulty of operating on fused anhy- 

 drous phosphoric acid. Phosphoric acid which has once obtained water cannot be 

 deprived of it by heat alone. When heated, the hydrated acid volatilizes. Upon sub- 

 jecting phosphoric acid, fused upon the ring end of a wire (401.), to the action of the 

 voltaic apparatus, it conducted, and was decomposed ; but gas, which I believe to be 

 hydrogen, was always evolved at the negative electrode, and the wire was not affected 

 as would have happened had phosphorus been separated. Gas was also evolved at 

 the positive electrode. From all the facts, I conclude it was the water and not the 

 acid which was decomposed. 



683. Arsenic acid. This substance conducted, and was decomposed ; but it con- 

 tained water, and I was unable at the time to press the investigation so as to ascertain 

 whether a fusible anhydrous arsenic acid could be obtained. It forms, therefore, at 

 present no exception to the general result. 



684. Nitrous acid, obtained by distilling nitrate of lead, and keeping it in contact 



* Db lk Rivb. 



