356 PERSONAL PREPARATION FOR RESEARCH. 



expect these products, they were a residual phenomenon , 

 the cause of which was. still to be found. Some chemists 

 thought that electricity had the power of producing these 

 substances of itself; and if their erroneous conjecture had 

 been adopted, succeeding researches would have gone upon 

 a false scent, considering galvanic electricity as a pro- 

 ducing rather than a decomposing force. The happier 

 insight of Davy conjectured that there might be some 

 hidden cause of this portion of the effect : the glass con- 

 taining the water might suffer partial decomposition, or 

 some foreign matter might be mingled with the water, 

 and the acid and alkali be disengaged from it, so that the 

 water would have no share in their production. Assuming 

 this, he proceeded to try whether the total removal of the 

 cause would destroy the effect, or at least the diminution 

 of it cause a corresponding change in the amount of effect 

 produced. By the substitution of gold vessels for the 

 glass without any change in the effect, he at once deter- 

 mined that the glass was not the cause. Employing dis- 

 tilled water, h^ found a marked diminution of the quantity 

 of acid and alkali evolved ; yet there was enough to show 

 that the cause, whatever it was, was still in operation. The 

 impurity of the water, then, was not the sole, but a con- 

 current cause. He now conceived that the perspiration 

 from the 'hands touching the instruments might affect the 

 case, as it would contain common salt, and an acid and an 

 alkali would result from its decomposition under the 

 agency of electricity. By carefully avoiding such contact, 

 he reduced the quantity of the products still further, until 

 no more than slight traces of them were perceptible.- 

 What remained of the effect might be traceable to im- 

 purities of the atmosphere, decomposed by contact with 

 the electrical apparatus. An experiment determined this : 

 the machine was put under an exhausted receiver, and 



