650 
ME. J. NORMAN LOCKYEE ON SPECTEUM-ANALYSIS 
electric spark these compounds are split up, and thus the true spectrum of the metals is 
obtained.” 
Two years later (in 1864) Mitscherlich, in a second communication*, expanded his 
views and brings an overwhelming mass of evidence in favour of them. The methods 
he employed were as follows : — 
The substances were heated : 
1. In the flame of a Bunsen burner. 
2. In the flame of coal-gas burning in oxygen. 
3. In the flame of hydrogen burning in chlorine. 
4. In the flame of mixtures of hydrogen and bromine or iodine-vapour burning in air 
or oxygen. 
5. In the case of combustible gases they were allowed to emerge out of the middle 
aperture of an oxyhydrogen burner, and were burnt in air or oxygen. 
In the case of non-combustible gases they were mixed with a combustible gas, such as 
carbonic oxide or hydrogen. 
6. In the case of solid substances they were introduced into a tube one end of which 
was connected with a Rose’s hydrogen-apparatus ; the substance was then volatilized, and 
the gas kindled at the other end of the tube. 
7. Or the spark was taken between poles containing the metal or compound in any gas ; 
or between, 
8. Liquid electrodes , in which the temperature is much lower than in 7. 
From the beautiful series of researches carried on by these several methods, he con- 
cludes “ that every compound of the first order which is not decomposed, and is heated 
to a temperature adequate for the production of light, exhibits a spectrum peculiar to 
this compound, and independent of other circumstances.” 
Bearing of the New Observations. 
The experiments I have lately made, taken in conjunction with my determination of 
the long and short lines of metallic vapours, and the consequent simplification of the 
spectra by the reduction of pressure or molecular distance, set this question at rest, and 
in the direction indicated by Mitscherlich, Clifton, Roscoe, and Diacon ; while much 
light has been thrown upon all the prior observations, as a consequence of which they are 
brought much more into harmony than at first appeared. 
First. I have observed f that whether the spectra of iodides, bromides, &c. be observed 
in the flame or weak spark, in air , the spectrum is in the main the same, as maintained 
by Ivirchhoff and Bunsen ; but that this is not the spectrum of the metal is established 
by the facts, that with a low temperature only the longest lines of the metals are present, 
showing that only a small quantity of the simple metal is present as a result of partial 
dissociation, and that by increasing the temperature, and consequently the amount of 
dissociation, the other lines of the metals appear in the order of their length with each 
rise of temperature. 
* Translated in Philosophical Magazine, 1864, vol. xxviii. p. 169. f See antb, p. 645. 
