A HISTORY OF SCIENCE 



ished plate of silver left, after evaporation, a black 

 stain, precisely similar to that produced by extremely 

 diluted nitrous acid. 



"After these results I could no longer doubt that 

 some saline matter existing in the agate tubes had been 

 the source of the acid matter capable of precipitating 

 nitrate of silver and much of the alkali. Four addi- 

 tional repetitions of the process, however, convinced me 

 that there was likewise some other cause for the pres- 

 ence of this last substance ; for it continued to appear 

 to the last in quantities sufficiently distinguishable, 

 and apparently equal in every case. I had used every 

 precaution, I had included the tube in glass vessels out 

 of the reach of the circulating air ; all the acting mate- 

 rials had been repeatedly washed with distilled water ; 

 and no part of them in contact with the fluid had been 

 touched by the fingers. 



" The only substance that I could now conceive as 

 furnishing the fixed alkali was the water itself. This 

 water appeared pure by the tests of nitrate of silver and 

 muriate of barytes; but potash of soda, as is well 

 known, rises in small quantities in rapid distillation; 

 and the New River water which I made use of contains 

 animal and vegetable impurities, which it was easy to 

 conceive might furnish neutral salts capable of being 

 carried over in vivid ebullition." * Further experi- 

 ment proved the correctness of this inference, and the 

 last doubt as to the origin of the puzzling chemical was 

 dispelled. 



Though the presence of the alkalies and acids in the 

 water was explained, however, their respective migra- 

 tions to the negative and positive poles of the battery 



52 



