and the Black Oaeide of Iron at a white heat. 179 



ruptive force on the molecules of water, as if chemical affinity 

 were but a kind of mechanical cohesion, which may be over- 

 come by division. On the other hand, however, it must not 

 be forgotten, that v/e are how acquainted with a large num- 

 ber of fulminating compounds, which can be decomposed 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 stability 

 of union : and if it shall appear that a feeble mechanical force 

 can overcome a small intensity of affinity, it will be acknow- 

 ledged as quite possible that a powerful mechanical agency 

 may overcome a great one. We have no means perhaps of 

 making an unexceptionable experiment as to the decomposing 

 power of mechanical force ; for we cannot bring it into play 

 without calling into action other agencies. If we touch, or 

 rub, or strike a fulminate, for example, we cause the evolution 

 of heat, and add its decomposing power to that of the mecha- 

 nical impulse. It would be a mere petitio principii, however, 

 to assume that the heat produced alone effects the decompo- 

 sition observed. It seems to me, therefore, that the decom- 

 position of steam by the electric spark furnishes a more 

 complex problem for solution than the action of M'hite-hot 

 platinum on the same compound does ; and that the experi- 

 ments made with the metal are more likely to throw light on 

 those tried with the spark, than to be explained by them. 



Whilst thinking over these difficulties, and the objections 

 to Mr. Grove's conclusions suggested by Herschel and Play- 

 fair, I had occasion to perform the familiar class-experiment 

 of burning iron wire in oxygen. I observed with an interest 

 I had not felt previously, although I had carelessly noticed 

 the phenomenon before, that bubbles of apparently perma- 

 nent gas rose from the globules of white-hot oxide of iron as 

 they fell into the water. It seemed to me possible that this 

 gas might be a mixture of oxygen and hydrogen separated by 

 the influence of the metallic oxide, acting as platinum did in 

 Mr. Grove's experiments. It was certain, moreover, that if 

 this should prove to be the case, it would supply a powerful 

 argument in favour of that gentleman's conclusion, which 

 seems, in spite of all the objections noticed, in the highest 

 degree probable, namely, that heat, apart altogether from the 

 medium through which it is applied, can resolve water into 

 its elements. 



As the following experiments were made solely in the hope 

 of substantiating Mr. Grove's view, which unfortunately, how- 

 ever, they leave exactly as they found it, I trust that gentle- 

 man will not consider their publication an interference with 

 his researches. I was led to try them incidentally, and 



N2 * 



