158 CORRELATION OF PHYSICAL FORCES. 



portion of 36 to 8. Numbers expressing their combining 

 weights, which are thus relative, not absolute, may by a con- 

 ventional assent as to the point of unity, be fixed for all chemi- 

 cal reagents ; and, when so fixed, it will be found that bodies, 

 at least in inorganic compounds, generally unite in those pro- 

 portions, or in simple multiples of them : these proportions 

 are termed Equivalents. 



Now a voltaic battery, which consists usually of alterna- 

 tions of two metals, and a liquid capable of acting chemically 

 upon one of them, has, as we have seen, the power of pro- 

 ducing chemical action in a liquid connected with it by metals 

 upon which this liquid is incapable of acting : in such case the 

 constituents of the liquid will be eliminated at the surfaces of 

 the immersed metals, and at a distance one from the other. 

 For example, if the two platinum terminals of a voltaic 

 battery be immersed in water, oxygen will be evolved at one 

 and hydrogen at the other terminal, exactly in the propor- 

 tions in which they form water ; while, to the most minute 

 examination, no action is perceptible in the stratum of 

 liquid. It was known before Faraday's time that, while this 

 chemical action was going on in the subjected liquid, a chemi- 

 cal action was going on in the cells of the voltaic battery ; 

 but it was scarcely if at all known that the amount of chemi- 

 cal action in the one bore a constant relation to the amount 

 of action in the other. Faraday proved that it bore a direct 

 equivalent relation : that is, supposing the battery to be 

 formed of zinc, platinum, and water, the amount of oxygen 

 which united with the zinc in each cell of the battery was 

 exactly equal to the amount evolved at the one platinum ter- 

 minal, while the hydrogen evolved from each platinum plate 

 of the battery was equal to the hydrogen evolved from the 

 other platinum terminal. 



Supposing the battery to be charged with hydrochloric 

 acid, instead of water, while the terminals are separated by 

 water, then for every 36 parts by weight of chlorine which 



