and the Black Oxide of Iron at a white heat, 183 



that water or any other liquid penetrates to the iron core, and 

 is subject to its influence. When this becomes known, it 

 need not surprise us that most of the globules should rapidly 

 decompose water. After observing this fact, I tried the 

 effect of thin and thick coils of wire, and found that the latter 

 invariably gave off the greater volume of gas. When the coil 

 is so thin that the metal all oxidizes, no gas is evolved at all. 

 A thick coil indeed furnishes a striking mode of illustrating 

 to a class the principle of Lavoisier's mode of decomposing 

 water, and forms a beautiful addition to the iron-wire expe- 

 riment. 



From these observations then, it would seem that white- 

 hot oxide of iron cannot decompose water in the way white- 

 hot platinum does. But before any conclusion can be drawn 

 from this fact inimical to Mr. Grove's views, or favourable to 

 the opinion that a specific property of the platinum has more 

 to do with the decomposition of water than its mere tempera- 

 ture has, we should require to know how far the two white- 

 hot bodies are to be considered as at the same temperature. 

 In Mr. Grove's experiments, platinum is raised to as high a 

 heat as it can bear without fusing. It must then be elevated 

 to a temperature much above that necessary to make iron 

 white-hot, or to fuse its oxide, for our forges can melt iron 

 and its oxides, but do not fuse platinum. It may also be re- 

 marked, that bright as the light emitted by burning iron is, 

 it falls short in intensity of that given off by platinum on the 

 verge of fusion. It seems accordingly probable, that during 

 the combustion of iron in oxygen the temperature never rises 

 high enough to confer upon the resulting oxide the power of 

 decomposing water. The question admits of direct decision, 

 by ascertaining whether oxide of iron, heated by the oxy- 

 hydrogen blowpipe to as high a temperature as fusing pla- 

 tinum, acquires the power of decomposing water without ap- 

 propriating to itself either of its elements. But it would have 

 been an interference with Mr. Grove's own researches to have 

 made experiments of this kind, and I have accordingly left the 

 question undecided. 



Meanwhile the experiments I have recorded are of some 

 little interest, as at least showing that not only a white heat, 

 but a high white heat, is essential to the successful perform- 

 ance of Mr. Grove's experiments. Unfortunately, we have 

 not at present any method of measuring high temperatures 

 which admits of ready application or secures great accuracy. 

 " W^hite heat " is in fact a vague expression for a range of 

 temperature, of the extremes in either direction or extent of 

 which we have no very precise knowledge. The power of 

 the eye to measure the relative intensities of the light evolved 



