392 NINETEENTH CENTURY. FT. in. 



Discovery of Electrolysis, or the Decomposition of 

 Substances by Electric Currents, 1800-18O6. In the 

 year 1800, two men named Nicholson and Carlisle discovered 

 by chance that when the two wires of a voltaic battery were 

 dipped in water, bubbles of gas rose up from them. They 

 also found by experiment that the gas from one wire was 

 oxygen, and from the other hydrogen ; but where these gases 

 came from, whether they were produced by the electricity, 

 or came from the battery, or from the water, they could not 

 tell. Moreover, besides the oxygen and hydrogen which 

 came off, there also appeared an acid of some kind at the 

 positive pole, as was shown by damp litmus paper turning 

 red (see p. 228), and an alkali appeared at the negative 

 pole which turned this red litmus paper blue again. This 

 looked as if the electric current had produced something in 

 the water ; for Cavendish, as you will remember, had shown 

 that pure water is made of oxygen and hydrogen only (see 

 p. 230). Many chemists, therefore, set themselves to try 

 to discover what effect the electric current had on the water, 

 and Davy in 1806 succeeded in solving the question. 



The history of his experiments is especially interesting, 

 because it shows, as we have noticed so often before, that a 

 patient and careful inquiry into nature always gains a true 

 answer in the end. Davy did not believe that the electric 

 current produced anything in the water; he thought that 

 both the acid and the alkali came from the vessels that were 

 used. So he set to work steadily to clear away all possibility 

 of impurities. He took distilled water, and used cups first 

 made of agate, and afterwards of pure gold, because he 

 found that the clay of the china cups was acted upon by the 

 cunent. Yet, in spite of these and many other precautions, 

 the acid and the alkali still continued to appear. Then he 

 used water which he had evaporated very slowly, instead 



