of the Metals developed by Exploding Gases. 1C5 



(that is, by reducing the quantity of lithium present in the 

 tube), the line could be reduced in width until it was no wider 

 than one tenth of the distance between the two sodium lines. 

 This seems to prove that the breadth of the line is directly 

 dependent on the amount of lithium present. 



M. Fievez has, in a recent publication (Bulletins de VAca- 

 de'mie roi/ale de Belgigue), concluded, from observations on 

 sodium, that the widening of the lines is solely due to eleva- 

 tion of temperature. The flash of the exploding gases cannot 

 be raised in temperature by the presence of a minute quantity 

 more of a lithium compound; so that in our case the widening 

 cannot be ascribed to any thing but the increase in the quan- 

 tity of lithium present, or to some consequence of that in- 

 crease. It is not improbable that the amount of lithium 

 vaporized in the front of the wave of explosion is less than in 

 the following part, and hence the absorption-line is not so 

 wide as the bright line behind it, while in the rear of the wave 

 the absorption extends over the whole width of the bright 

 band, and so is not so easily noticed. Only twice amongst 

 many observations was any reversal of the lithium line seen 

 in the receding wave of explosion. 



On observing the flash with a spectroscope of small disper- 

 sion instead of that with the grating, the continuous spectrum 

 was very bright, but the metallic lines stood out still brighter; 

 not only the red line of lithium, but the orange, the green, 

 and the blue lines were very bright, and continued so when 

 the pressure of the gases before explosion was reduced from 

 one atmosphere to one third of an atmosphere. The violet 

 line was not seen, but it may have been so much expanded as 

 to be lost in the continuous spectrum ; for it showed in a 

 photograph afterwards taken. Other lines were, however, 

 seen — the sodium yellow lines, the calcium indigo line, a group 

 of other blue lines, and a group of green lines, amongst which 

 one line was conspicuous, and this line, by comparison with 

 the solar spectrum, was identified with E. We had not ex- 

 pected to see any lines of iron, as iron and its compounds 

 give no lines in the flame of a Bunsen burner, and we sup- 

 posed that it would only be volatilized at a much higher 

 temperature. But the appearance of E suggested that other 

 of the green and blue lines might be due to iron; so we pro- 

 ceeded to compare the positions of these lines with those of 

 the electric spark between iron electrodes. For this purpose 

 one of the spark-lines was first brought carefully on to the 

 pointer, or cross wires, in the eye-piece of the observing tele- 

 scope, and then, the passage of the spark being stopped, the 

 flash of the exploding gases was observed. It was not diffi- 



