50 ESSAYS BIOGRAPHICAL AND CHEMICAL 



cotton wick, an acid appeared round the positive wire, and 

 an alkali round the negative wire. Davy showed by a 

 series of convincing experiments that the alkali is usually 

 potash or soda derived from the glass, and the acid 

 usually hydrochloric acid from the common salt present 

 as an impurity in the water. From experiments such as 

 these he evolved a theory that all substances which have 

 a chemical affinity for each other are in opposite states of 

 electrification, and that the positive pole attracts those 

 constituents of the solution which possess a negative 

 charge, while the negative pole attracts the positively 

 charged component. The more powerful the battery, 

 the greater the force of these attractions and repulsions. 

 For example, oxygen and acids are negative bodies, for 

 they are attracted by the positive pole, and liberated 

 there; whereas metals and their oxides, and hydrogen, 

 nitrogen, carbon, and selenium are positive, because they 

 separate at the negative pole. It ought, therefore, to be 

 possible, by help of a sufficiently strong electric current, 

 to decompose any compound whatsoever. Davy carried 

 his inference farther, and suggested that the reason of 

 chemical attraction is the oppositely charged state of the 

 components of a compound. A compound is an elec- 

 trically neutral body, for the constituents of the com- 

 pound, in uniting, have respectively equal and opposite 

 charges, which neutralise each other by the act of com- 

 bination. But a current of electricity, passing through 

 such a compound, might neutralise the electricity in each, 

 and so, by overcoming their attractions, decompose the 

 compound. 



By applying these ideas, he succeeded in decomposing 

 the ' fixed alkalies,' as caustic soda and potash used to be 

 called, into oxygen, hydrogen, and the metals sodium and 

 potassium. Having failed to obtain any products from 

 aqueous solutions of these compounds, except oxygen and 



