168 Dr. Faraday's Experimental Researches in Electricity. 



peared 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 possession to allow me to decide the 

 point satisfactorily. My belief is, that when sulphur 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 electroly- 

 zable (757.). 



682. Phosphoric acid is, I believe, also in the same condi- 

 tion ; but I have found it impossible to decide the point, be- 

 cause of the difficulty of operating on fused anhydrous phos- 

 phoric acid. Phosphoric acid which has once obtained water 

 cannot be deprived of it by heat alone. When heated, the 

 hydrated acid volatilizes. Upon subjecting 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 contained 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 acidj obtained by distilling nitrate of lead, 

 and keeping it in contact with strong sulphuric acid, was found 

 to conduct and decompose slowly. But on examination there 

 were strong reasons for believing that water was present, and 

 that the decomposition and conduction depended upon it. I 

 endeavoured to prepare a perfectly anhydrous portion, but 

 could not spare the time required to procure an unexception- 

 able result. 



685. Nitric acid is a substance which I believe is not de- 

 composed directly by the electric current. As I want the 

 facts in illustration of the distinction existing between primary 

 and secondary decomposition, I will merely refer to them in 

 this place (752.). 



686. That these mineral acids should confer facility of con- 

 duction and decomposition on water, is no proof that they are 

 competent to favour and suffer these actions in themselves. 

 Boracic acid does the same thing, though not decomposable. 

 M. De la Rive has pointed out that chlorine has this power 

 also ; but being to us an elementary substance, it cannot be 

 due to its capability of suffering decomposition. 



687. Chloride of sulphur does not conduct, nor is it decom- 



