of the Metals developed by Exploding Gases. 169 



Thus far the experiments had been made with the gases at 

 the atmospheric pressure, or nearly so, before ignition. The 

 proportions of hydrogen and oxygen were nearly two to one; 

 but an excess of either gas to the extent of one fifth did not 

 sensibly affect the results. 



Other explosive mixtures were tried. Carbonic oxide with 

 oxygen, and marsh-gas with oxygen, developed in general 

 the same lines as the hydrogen mixture, but gave a much 

 brighter continuous spectrum. Sulphuretted hydrogen, ar- 

 seniuretted hydrogen, and antimoniuretted hydrogen, exploded 

 with oxygen, also gave very bright continuous spectra, but 

 no lines attributable to sulphur, arsenic, or antimony. 



We have also tried explosions at higher pressures ; mixtures 

 of hydrogen, carbonic oxide, and marsh-gas respectively, with 

 oxygen, were compressed into the tube by a condensing 

 syringe until the pressure reached two and a half atmospheres, 

 and in some cases three and a half atmospheres. The general 

 effect of increasing the pressure was to strengthen very much 

 the continuous spectrum, and also to intensify the bright 

 lines, so that photographs could be taken with a smaller num- 

 ber of explosions. The lines previously observed to be re- 

 versed were more strongly reversed, but no new lines which 

 we can attribute to the metals employed were noticed. No 

 iron line more refrangible than T showed itself in the photo- 

 graphs. But a banded spectrum, of which traces had been 

 noticed in the flash of the gases at lower pressure, came out 

 decidedly. This spectrum occupies the region between P and 

 R; it is not a regularly channelled spectrum, though pro- 

 bably under higher dispersion it would resolve itself into 

 groups of lines like the water-spectrum. In fact it seems to 

 us most probable that it is a development of the water-spectrum, 

 dependent on the pressure. 



It seems very remarkable that metals so little volatile as 

 iron, nickel, and cobalt should develop so many lines* in the 

 flash, while more volatile metals show few or no lines. We 

 do not know that any lines attributed to the metals, as dis- 

 tinct from their compounds, which have been observed in the 

 gas-flame cannot be seen also in the flash of the exploding 

 gases, unless they be the blue lines of zinc which Lecoq de 

 Boisbaudran has seen faintly in the gas-flame when zinc 

 chloride was introduced. These are, however, so faint in the 

 flame, that they might easily escape notice in the much 

 stronger continuous spectrum of the flash. But iron, nickel, 

 and cobalt show no lines of those metals in a gas-flame. 

 Mitscherlich {Ann. d. Phys. u. Chem. Bd. 121, St. 3), by 



* For detailed list of these lines see Proc. Roy. Soc. vol. xxxvi. pp. 473-5. 



