172 Spectral Lines of Metals developed by Exploding Gases. 



the explosions being those most strongly reversed in the 

 photographs of the carbon-tube. The greater complete- 

 ness and extent of the iron spectrum, as well as the pre- 

 sence of the aluminium lines, which are entirely wanting 

 in the explosion-spectrum, indicate that the temperature of 

 the tube was higher than that of the explosion. That 

 iron, nickel, and cobalt are volatile in some degree at the 

 temperature of the explosion appears to be proved, and 

 makes the appearance of iron lines at the very apices of solar 

 prominences, as observed by Young, less astounding than it 

 seemed to be at first sight. The ascending current of gas 

 making the prominence may very well carry iron vapour with 

 it; or we may not unreasonably suppose that there is meteoric 

 dust containing iron everywhere in the outer atmosphere of 

 the sun, which becomes volatilized, and emits the radiation 

 observed, when it is heated up by the hot current of the pro- 

 minence. What the temperature of such a current may be 

 we cannot well gauge, but it is high enough to give the 

 hydrogen -spectrum, of which no trace has been observed in 

 the flash of the explosions or in the oxyhydrogen-jet. The 

 temperature of the explosions we know with tolerable accu- 

 racy, at least when the gases are at atmospheric pressure to 

 begin with. Bunsen (Phil. Mag. 18G7, p. 41)4) found the 

 pressure of the explosion was for hydrogen and oxygen 9*6 

 atmospheres, and for carbonic oxide and oxygen 10*3 atmo- 

 spheres, and he calculated the corresponding temperatures to 

 be 2844° and 3033°. Recently published observations by 

 Berthelot and Yieille (Comptes ltendus, 1884, p. 548) put the 

 pressure of explosion of oxygen and hydrogen at 9*8 atmo- 

 spheres and of carbonic oxide and oxygen at 10*1, and the 

 corresponding temperatures 3240° and 3334°. The pressures 

 determined by the two observers agree closely, and the calcu- 

 lated temperatures are not very discordant. On the whole, 

 we cannot be wrong in assuming the temperature of the 

 exploding gases to be about 3000°; and we see that at this 

 degree such metals as iron, nickel, and cobalt are vaporous 

 and emit many characteristic rays, and that by far the greatest 

 part of these rays lie between narrow limits of refrangibility 

 G and P. Even for other metals there is a predominance of 

 rays in the same part of the spectrum. The lines of lead, 

 potassium, and manganese, three out of four lines of thallium, 

 and two thirds of those of chromium, observed in the explo- 

 sions, fall within the same region. It must not be inferred 

 that these facts indicate the limit of the rate of oscillation 

 which can be set up in consequence of an elevation of tempe- 

 rature to 3000 u ; because we know that the spectrum of the 



