1819.] History and Present State of Galvanism. 137 



Davy's pile served merely the purpose of screening one side of 

 the zinc, while the other side was freely exposed to the action 

 of the nitric acid. 



Trommsdorfs discovery of the efficacy of large metallic plates 

 in producing combustion was the next step in the improvement 

 of the apparatus. This discovery was verified by Fourcroy, 

 Thenard, and Vauquelin. These gentlemen found that the elec- 

 trical action of the battery was not increased by the increase of 

 the size of the plates, but by the increase of the number of pairs ; 

 but the chemical action, as far as combustion is concerned, and- 

 as far as the decomposition of those bodies which are not very 

 difficult of decomposition, is increased with the size of the plates. 



3. But the most important addition made to our knowledge of 

 galvanic decomposition is contained in a paper written by Hisin- 

 ger and Berzelius, and published in the first volume of Gehlen's 

 Journal, in 1803. They ascertained by a copious induction that 

 when bodies are decomposed by galvanism, oxygen and acids are 

 accumulated round the positive pole ; while hydrogen, alkalies, 

 earths, and metals, are accumulated round the negative pole. Sir 

 H. Davy verified this law of Berzelius with much sagacity, in a 

 paper which constitutes one of the finest examples of experi- 

 mental investigation any where to be met with. He showed that 

 the acid and the alkali, which were affirmed to be formed when 

 water was decomposed by galvanism, and to accumulate round 

 the positive and negative wires, respectively owed their origin 

 to the decomposition of some common salt found either in the 

 water or in the vessel in which the water was kept ; and that 

 when perfectly pure water is used, and vessels quite free from all 

 contamination of salt, the water is decomposed without the 

 evolution or formation of any thing, except oxygen and hydrogen. 

 Davy, after verifying Berzelius's discovery, and tracing the way 

 in which the decomposed constituents penetrate to the respective 

 poles, went a step further. In his opinion, every body in nature 

 possesses a certain permanent electric state. Their affinity 

 for each other depends upon this state. If they be in the same 

 state, they have no affinity for each other; if they be in opposite 

 states, they have an affinity, and this affinity is the greater the 

 more intensely opposite the electrical states of the two bodies 

 are. If, therefore, we wish to decompose a compound, we have 

 only to bring its constituents to the same electric state, they 

 will in consequence of this separate of themselves. Now galva- 

 nism affords us this means. We have only to put it in practice 

 and it will enable us to decompose compounds, the constituents 

 of which are so intimately combined as to have resisted all 

 former efforts to separate them. This theory was applied with 

 the happiest success by Davy to the decomposition of the fixed 

 alkalies, and even of the alkaline earths. Boracic acid was 

 afterwards decomposed by Gay-Lussac and Thenard ; and suffi- 

 cient evidence was brought by Davy, Berzelius, and Stromeyer, that 

 silica is a compound of oxygen, and a combustible basis. Such 



