Conditions of the Constitution of Electrolytes. 167 



and being proportionate to the quantity of elements separated 

 (821.). I may not, however, stop to discuss this point ex- 

 perimentally at present. 



678. When a compound contains such elements as are 

 known to pass towards the opposite extremities of the voltaic 

 pile, still the proportions in which they are present appear to 

 be intimately connected with capability in the compound of 

 suffering or resisting decomposition. Thus, the protochloride 

 of tin readily conducts, and is decomposed (402.), but the 

 perchloride neither conducts nor is decomposed (406.). The 

 protiodide of tin is decomposed when fluid (402.); the per- 

 iodide is not (405.). The periodide of mercury when fused 

 is not decomposed (691.), even though it does conduct. I was 

 unable to contrast it with the protiodide, the latter being con- 

 verted into mercury and periodide by heat. 



679. These important differences induced me to look more 

 closely to certain binary compounds, with a view of ascertain- 

 ing whether a law regulating the decomposability according to 

 some relation of the proportionals or equivalents of the ele- 

 ments, could be discovered. The proto compounds only, 

 amongst those just referred to, were decomposable ; 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, chlo- 

 rides, and iodides subject to it, except the chloride of anti- 

 mony and the periodide of mercury, (to which may now per- 

 haps 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 general result were such bodies as the sul- 

 phuric, 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 de- 

 composable by, electricity, although I had previously 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 posi- 

 tive electrode, although much is absorbed (728.), and hydro- 



fen and sulphur appear at the cathode, or negative electrode. 

 Jow the hydrogen has with me always been pure, not sul- 

 phuretted, and has been deficient in proportion to the sulphur 

 present, so that it is evident that when decomposition oc- 

 curred water must have been decomposed. I endeavoured to 

 make the experiment with anhydrous sulphuric acid. It ap- 



* De la Rive. 



