342 Hari'LET and Ramage — Banded Flame-Spectra of Metals, 



bauds are degraded towards the more refrangible end of the spectrum. The lines 

 and bands have been described more or less perfectly by several observers, but the 

 most complete account has been given by Liveing and Dewar.* They describe a 

 flame-spectrum of magnesium, consisting of flutings which they attribute to a 

 combination of hydrogen with magnesium, and suppose it may be a chemical com- 

 pound formed only within certain limits of temjjerature and dependent for its 

 stability on the pressure of the gaseous element, like the instance of the hydrides 

 of palladium, sodium, and potassium, investigated by Troost. 



In attempting to photograph the flame-spectra of zinc and cadmium, the corre- 

 sponding triplets in the visible spectrum were easily obtained ; and in the spectrum 

 of cadmium, a strong line of wave-length 3261 was also photographed. Traces 

 of weak band-spectra were photographed in the violet part of the spectrum in 

 each case ; but it was only after many attempts that photographs were obtained 

 upon which the bands were seen to be strongly marked. 



The lines of impurities, such as lead, indium, thallium, &c., are much stronger 

 in the jihotographs of some samples of " j3ure" metals than even those character- 

 istic of the " pure " metals themselves. This is a proof of the low emissive power 

 of the radiant molecules of the elements in the oxyhydrogen flame. It may 

 perhaps be attributed to a smaller degree of volatility and greater heat of com- 

 bustion, with less volatility of the oxide. The heat of combustion cannot, 

 however, be the explanation in the case of mercury ; neither can the volatility of 

 the oxide. There may be a more profoimd cause for such a difference in these 

 spectra, arising out of a peculiar mode of vibration set up within the ether by the 

 monatomic molecules of the metals. 



It is possible that a flame of a higher temperature will be required to produce 

 the bands in a stronger degree. This is known to be the case with the lines 

 of mex'cury.'f The bands of zinc and cadmium were photogi'aphed with greatest 

 success by heating the respective metals on cyanite supports in the oxyhydrogen 

 flame, the spectra being received on a " Cadett Lightning Spectrum plate " ; the 

 time of exposure was for zinc 30 minutes, and for cadmium 20 minutes. The 

 bands in these spectra are degraded towards the ulti-a-violet, and the lines of 

 which they are composed are nebulous. The spectra are very complex. There 

 appear to be two well-marked bands in each spectrum, and the two spectra are 

 very similar in constitution. In addition to the two bands, weaker lines, which 

 are components of other bands, are visible, and can be traced to the edge of the 

 plate, wave-length 3530. 



We were unable to photograph either lines or bands of mercury when its 

 oxide, used as a convenient source of the metal, was heated in the oxyhydrogen 

 flame. Both Mitscherlich and Liveing have observed lines in the spectrum of 



*Proc. Roy. Soc, vol. 32., 1881, p. 189. f ^itsclierlich, Phil. Mag., 1864, p. 178. 



