and the Black Oxide of Iron at a white heat, 245 



should be converted into sensible heat, either the steam would be 

 converted into permanent air, or some other change would take place 

 in its constitution.* 



In the greater number of Mr Grove's experiments, water was 

 raised in temperature through the medium of platinum ; and it be- 

 came a question accordingly, as Sir John lierschel and my friend 

 Dr Lyon Playfair suggested, how far the decomposition of water 

 observed was owing to the mere heat of the metal, how far to the 

 peculiar surface -influence, or so-called catalytic force, which has 

 been so long recognised as possessed by platinum and the other 

 noble metals. Dr Playfair also referred to the fact, " that many 

 bodies at high temperatures exhibited a great affinity for oxygen, 

 which they did not possess at lower temperatures ; as, for instance, 

 silver, gold, and even platinum itself, which metals absorb oxygen 

 when intensely heated, and give it out again on cooling. If the ex- 

 periments had been tried in tubes of quartz or silica, they would not 

 have been open to the objection which the use of so peculiar a metal 

 as platinum appeared to involve."! 



There was indeed one form of Mr Grove's experiment not liable 

 to the exception urged against those where platinum was used. He 

 found it quite possible to decompose steam by sending Leyden-jar 

 discharges through it, and refers the decomposition solely to the heat 

 evolved by the electric spark. The same view has been suggested 

 as not improbable by Faraday, in relation to the decomposition of 

 water in the liquid form by electric discharges.]: With great diffi- 

 dence, however, I would remark, that the spark decomposition of 

 water cannot be regarded as an experimentum crucis. Although 

 the electric spark cannot decompose steam electrolytically, we may 

 not at once infer that it cannot decompose it in another way. I 

 have no wish to assert that it can, but it is possible that it may, and 

 a crucial experiment should be unexceptionable. Again : the spark 

 discharge of a Leyden-jar exerts a great disruptive force, and acts 

 topically with much violence. There is reason moreover to believe 

 that mechanical agitation or disturbance of a chemical compound 

 can in many cases cause the separation of its elements. It may 

 seem an extravagant idea to suppose that oxygen may be torn or 

 detached from hydrogen by the action of a disruptive force on the 

 molecules of water, as if chemical affinity were but a kind of me- 

 chanical cohesion, which may be overcome by division. On the other 

 hand, however, it must not be forgotten, that we are now acquainted 

 with a large number of fulminating compounds, which can be de- 

 composed by friction, by a touch, or a stroke. These compounds 

 are all fragile, and water is a very stable combination ; but fragility 

 and stability are but terms of degree, in relation to Chemical 



» Phil. Trans. 1783, p. 416. 



t Athenaeum for September 19, 1846, p. 966. 



+ Researches in Electricity, 3(1 Series, paragraph 33' 



