and the Black Oxide of Iron at a white heat. 249 



Tlie volume of hydrogen however given off in some of the trials, 

 when the product of combuBtion was placed in acid, was very con- 

 siderable. A graduated gas jar was filled with dilute sulphuric acid, 

 and inverted over a small capsule containing 100 grains of the 

 crushed globules, which was placed in a basin also containing dilute 

 acid. By this arrangement the gas was collected and measured at 

 the same time, without risk of mixing with air, or necessity for 

 watching the process, which is a slow one. 100 grains treated in 

 this way gave off 16 cubic inches of hydrogen, corresponding to 9 

 grains of iron. The experiment was accidentally stopped at this point 

 whilst the gas was still rising in undiminished quantity. 



Metallic iron, then, was certainly present in many of the globules, 

 and of this I had direct ocular demonstration. On crushhig some 

 of them in a mortar, they were found to separate into a shell of 

 pulverizable oxide, and a core of iron which formed a nearly spheri- 

 cal pellet. In one case 50 grains of the globules were crushed, the 

 pellets separated, and the residue placed in diluted sulphuric acid. 

 It did not evolve a trace of hydrogen in the course of twenty-four 

 hours. The pellets were then added to the same acid, and gave off 

 12 cubic inches of gas = 1 3*6 per cent, of iron in the globules.* 

 The shell of oxide is frequently imperfect or perforated, so 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 thick and thin coils of wire, 

 and found that the former invariably gave off the greater volume of 

 gas. When the coil is so thin that the metal is all oxidized, 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 decompos- 

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

 ment. 



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 temperature 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 tempera- 

 ture 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 remarked, that bright as the light 



* In none of the experiments was the thermometer or barometer specially 

 observed, as minute accuracy was not aimed at. 



VOL. XLIII. NO. LXXXVr. — OCTOBER 1847. R 



