CHEMISTRY OF THE NINETEENTH CENTURY. 609 



to say, of splitting water up into its elements. This was accomplished 

 by the then newly-found agency of the galvanic battery. The experi- 

 ment is probably familiar to most of our readers, as in some such form 

 as that shown in Fig. 309 it is frequently exhibited at popular lectures. 

 A wire from each pole of the battery F passes at a through the bottom 

 of the vessel A, which contains water acidulated with a little sulphuric 

 acid. Over each a tube entirely filled with the same liquid is inverted at 

 the commencement of the experiment. When the battery connections 

 are made, a stream of minute bubbles of gas is seen to rise from each 

 wire. The gas gradually displaces the water in the tubes, and the gas 

 rising from the negative pole is found to be pure hydrogen, and that 

 from the positive pole pure oxygen. The bulk of the hydrogen is 

 always twice that of the oxygen. As Dumas' experiment for accurately 

 determining by synthesis the ponderal composition of water is regarded 

 by chemists as classical, a representation of the apparatus is given in 

 Fig. 312, and this, with the description, will enable the reader to 

 understand it" without further details. 



Now, in the experiments on the electric decomposition of water, 

 made at the beginning of the present century, chemists were perplexed 

 in finding that even when water supposed to be quite pure was exposed 

 to the action of a current of electricity, the liquid about the negative 

 pole always showed traces of alkali, while at the positive pole traces 

 of acid appeared. As it had been proved in other ways that water 

 contained only oxygen and hydrogen, the constant appearance of acid 

 and alkali at the respective poles induced certain chemists to imagine 

 that some substances other than oxygen and hydrogen might be present 

 in water, while other chemists held that the acid and alkali were in 

 some way produced by the action of the current. Davy tried to 

 eliminate any effect due to the material of the vessel holding the 

 water by using small cups of agate. Still acid and alkali appeared at 

 the poles. He substituted conical vessels of pure gold ; but still indi- 

 cations of acid and alkali were perceptible. Davy then placed his gold 

 cups under the receiver of an air-pump. When the electric action was 

 made thus to take place in a space free from every trace of nitrogen, 

 the water in neither of the connected gold cups showed any trace of 

 acid or of alkali. Thus was it conclusively proved that water chemi- 

 cally pure is decomposed by electricity into nothing but the two gases 

 oxygen and hydrogen. 



Davy proposed a theory of the relations of electricity to the ele- 

 mentary bodies very similar to that which was soon afterwards more 

 clearly announced by Berzelius. The chemical origin of the electric 

 force of the galvanic battery was another of Davy's views. 



By the agency of electricity in the form of currents from galvanic 

 batteries of many pairs of plates, Davy was able, in 1807, to decom- 

 pose several of the " earths" so as to obtain their metallic elements. 

 In this way he separated calcium, the metal of lime ; barium, the metal 



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