CH. xx DISSOCIATION 515 



Grove's experiments on the dissociation of water 



(1847). This difficulty was first overcome by Grove, who 

 showed in 1847 (Bakerian Lecture, Phil. Trans., 1847, 137, 

 1-16) that the combination of hydrogen and oxygen to form 

 water was partially reversed at high temperatures, e.g. by heat- 

 ing a platinum wire in steam by an electric current, by pass- 

 ing sparks through steam between platinum points, and by 

 plunging the fused end of a platinum wire under cold water. 

 Under these conditions bubbles of gas were produced, 

 which could be collected and detonated. 



In these experiments a small quantity of steam is decom- 

 posed into its elements as shown by the equation 



2H 2 O -> 2H 2 + O 2 . 



As recombination is checked by dilution with a large 

 volume of steam, the mixed gases can be cooled to 100 

 without recombining ; below this temperature the mixture 

 is quite stable, even when the steam is condensed, but 

 detonates in the ordinary way when ignited. The maximum 

 amount of gas collected was about 7 ^nr of the volume of 

 the steam. 



The dissociation of water may be represented by the 

 scheme 



in which the main course of the action is represented by a 

 full arrow, and the slight reversal by a dotted arrow. 



Deville's experiments on the dissociation of water (1863) 

 and of carbonic anhydride. Grove's experiment was 

 repeated on a larger scale in 1863 by Deville (Comptes 

 rendus, 1863, 56, 322), who poured i to 2 kilogrammes of 

 fused platinum into water and so secured an abundant 

 liberation of explosive gas. 



Deville also proved the dissociation of water by passing a 

 stream of carbonic anhydride, saturated with water-vapour 

 at 90 to 95 C, through a porcelain tube packed with pieces 



L L 2 



