640 
ME. J. NOEMAN LOCIvYEE ON SPECTEIJM- ANALYSIS 
I. CHEMICAL COMPOUNDS. 
In extension of the former experiments to which I have alluded, it became of import- 
ance to try several series of salts in which the atomic weights varied : 
1st. In each series. 
2nd. In the associated elements in each series. 
With this view the spectra of the following series were mapped : — 
PbF 2 , 
PbCl 2 , 
PbBr 2 , 
Pb I 2 ; 
Sr F 2 , 
Sr Cl 2 , 
SrBr 2 , 
Sr I 2 ; 
Ba F 2 , 
Ba Cl 2 , 
Ba Br 2 , 
Ba I 2 ; 
MgF 2 , 
Mg Cl 2 , 
Mg Br 2 , 
Mg I 2 ; 
Na F, 
Na Cl, 
Na Br, 
Na I. 
Conditions of the Experiments. 
The conditions of the experiments were as follows : — The salts were rammed into the 
small aluminium cups described in the former paper, and the cups fastened to copper 
rods which passed through a cork into the interior of a wide glass tube. An aluminium 
point'* formed, as in the former experiments, the opposite pole, which was also fastened 
to a copper rod passing through a cork fitted into the opposite end of the tube. Both 
corks were pierced and furnished with narrow glass tubes ; one of these served 
to admit hydrogen, while the opposite one served as an exit-tube for the gas. The 
hydrogen was prepared from zinc and sulphuric acid, and passed first through a scrubber 
filled with broken pumice-stone saturated with solution of plumbic acetate to free it from 
sulphuretted hydrogen, then through a wash-bottle containing concentrated sulphuric 
acid, and lastly through a tube containing fragments of sodium, the latter serving both 
as a drying tube and freeing the gas from any acid mechanically carried over by it. 
The hydrogen thus purified was admitted in a gentle stream into the tube containing 
* “ An examination of the spectrum of the spark by the new method shows that the light given out by the 
discharge depends upon the amount of vapour lying between the poles, and that if both poles are composed of 
equally volatile metals, or the same metal, the bridge is formed by an equal, or nearly equal, amount of vapour 
lying round each pole ; hence, supposiug that the vapours do not intermingle, it follows that the longest line 
can only be half the length of the actual distance between the poles. 
“ When, however, the poles are unequally vola tile, the bridge appears to be formed entirely of vapour from 
the most volatile pole ; hence the longest line can extend almost or quite across the space from pole to pole. 
“ It was on account of these observations that aluminium was used for the poles in the experiments described, 
it having been found that that metal was extremely refractory in the spark, i. e. that all its lines in the most 
visible portions of the spectrum were very short — the vapour which extended above the short line region being 
practically capable of giving but the two lines of aluminium which fall between H t and H 2 . 
“ There are, however, many phenomena in connexion with this which are well worth study ; for instance, in 
a case where the spectrum of copper was examined with a plumbago point opposite to the copper pole, the effect 
of the former was shown by the remarkable way in which the copper lines were shortened. Even when the 
poles were almost touching, the copper lines were confined to the copper pole, and did not extend across the 
spectrum .” — Extracts f rom Laboratory Notebook, 23rd September and 30th October, 1872. 
