258 Dr. Faraday's Experimental Researches in Electricity. 



which escaped when weak solutions of sulphurous acid were 

 used. 



757. Sulphuric Acid. — I have already given my reasons for 

 concluding that sulphuric acid is not electrolyzable, i. e. not 

 decomposable directly by the electric current, but occasionally 

 suffering by a secondary action at the cathode from the hydro- 

 gen evolved there (681.). In the year 1800, Davy considered 

 the sulphur from sulphuric acid as the result of the action of 

 the nascent hydrogen*. In 1804-, Hisinger and Berzelius 

 stated that it was the direct result of the action of the voltaic 

 pilef ; an opinion which from that time Davy seems to have 

 adopted, and which has since been commonly received by all. 

 The change of my own opinion requires that I should correct 

 what I have already said of the decomposition of sulphuric 

 acid in a former series of these Researches (552.): I do not 

 now think that the appearance of the sulphur at the negative 

 electrode is an immediate consequence of electrolytic action. 



758. Muriatic Acid. — A strong solution gave hydrogen at 

 the negative electrode, and chlorine only at the positive elec- 

 trode ; of the latter, a part acted on the platina and a part 

 was dissolved. A minute bubble of gas remained ; it was not 

 oxygen, but probably air previously held in solution. 



759. It was an important matter to determine whether the 

 chlorine was a primary result, or only a secondary product, 

 due to the action of the oxygen evolved from water at the 

 anode upon the muriatic acid ; i. e. whether the muriatic acid 

 was electrolyzable, and if so, whether the decomposition was 

 definite. 



760. The muriatic acid was gradually diluted. One part 

 with six of water gave only chlorine at the anode. One part 

 with eight of water gave only chlorine; with nine of water, a 

 little oxygen appeared with the chlorine : but the occurrence 

 or non-occurrence of oxygen at these strengths depended, in 

 part, on the strength of the voltaic battery used. With fifteen 

 parts of water, a little oxygen, with much chlorine, was evolved 

 at the anode. As the solution was now becoming a bad con- 

 ductor of electricity, sulphuric acid was added to it: this 

 caused more ready decomposition, but did not sensibly alter 

 the proportion of chlorine and oxygen. 



761. The muriatic acid was now diluted with 100 times its 

 volume of dilute sulphuric acid. It still gave a large propor- 

 tion of chlorine at the anode, mingled with oxygen ; and the 

 result was the same, whether a voltaic battery of 40 pairs of 



* Nicholson's Quarterly Journal, vol. iv. pp. 280, 281. 

 t Annates de Chimie, 1804, torn. li. p. 173. 



