386 ELEMENTARY LESSONS ON [CHAP. xi. 



(/.) Where the ions are gases, pressure affects the 

 conditions. Under a pressure of 300 atmospheres acid- 

 ulated water is not electrolysed, and behaves as an 

 insulator. 



(/.) The chemical work done by a current in an 

 electrolytic cell is proportional to the minimum electro- 

 motive-force of polarisation. 



(/.) Although the electromotive-force of polarisation 

 may exceed this minimum, the work done by the current 

 in overcoming this surplus electromotive-force will not 

 appear as chemical work, for no more of the ion will be 

 liberated ; but it will appear as an additional quantity of 

 heat (or " local heat ") developed in the electrolytic cell. 



(m.) Ohm's law holds good for electrolytic conduction 

 as well as for metallic conductors. 



(n.) Amongst the secondary actions which may occur 

 the following are the chief: (i.) The ions may them- 

 selves decompose ; as SO 4 into SO 3 + O. (2.) The ions 

 may react on the electrodes ; as when acidulated water 

 is electrolysed betwee'n zinc electrodes, no oxygen being 

 liberated, owing to the affinity of zinc for oxygen. (3.) 

 The ions may be liberated in an abnormal state. Thus 

 oxygen is frequently liberated in its allotropic condition 

 as ozone, particularly when permanganates are electro- 

 lysed. The " nascent " hydrogen liberated by the elec- 

 trolysis of dilute acid has peculiarly active chemical 

 properties. So also the metals are sometimes deposited 

 abnormally : copper in a black pulverulent film ; anti- 

 mony in roundish gray masses (from the terchloride 

 solution) which possess a curious explosive property, etc. 



418. Hypotheses of Grotthuss and of Clau- 

 sius. A complete theory of electrolysis must explain 

 firstly, the transfer of electricity, and, secondly, the transfer 

 of matter, through the liquid of the cell. The lafter 

 point is the one to which most attention has been 

 given, since the " migration of the ions " (i.e. their trans- 

 fer through the liquid) in two opposite directions, and 



