644 
MR. J. NORMAN LOCIvTER ON SPECTRUM-ANALYSIS 
there can be no doubt that it is the caesium line, and that it is due to the presence of a 
trace of caesium existing as an impurity in the lithium, as it does not appear in the 
spectrum of the pure salts ; and no one but Dr. Huggins has seen it in lithium, at any 
rate with sufficient distinctness to consider himself justified in including it in a map 
or list. 
Lithic Chloride gave 6705-2, the red line, thin and faint, but all across the spectrum; 
the orange very bright and across the spectrum ; the blue line was also visible, but it 
did not extend across the spectrum. 
It will be seen from the above that lithium, the least electro-positive of the alkali 
metals, approaches in its spectroscopic behaviour the metals of the alkaline earths, 
strontium and barium, as it approaches them in some points of its chemical behaviour. 
Thus the spectrum of its iodide differs from that of the chloride as the spectrum of baric 
iodide differs from that of baric chloride, and not as the spectrum of sodic iodide does 
from sodic chloride, as might have first been supposed from the usual position, among 
the alkalies, assigned to the metal. 
On the difference between Flame-sjpectra and those produced by a weak electric discharge. 
The following experiments were made with beads of the various substances mentioned, 
heated in the Bunsen flame on loops of platinum wire. 
Barium. 
Baric Iodide. — This salt gave the spectrum since proved to be due to the oxide and 
the line 5534-5 very distinctly ; it coloured the flame a greenish yellow, and fused to a 
globule. 
Baric Bromide gave the oxide spectrum and 5534-5 with difficulty; the spectrum was 
not very bright, and the flame but little coloured. 
Baric Chloride gave the same spectrum as the two salts mentioned above ; but the 
spectrum was much brighter, and the flame was coloured a bright pale green. 
Baric Fluoride gave scarcely a trace of the oxide spectrum, and 5534-5 was very faint 
indeed ; but no signs of fusion were visible, no bead being formed, and the flame was only 
coloured slightly and in parts. 
Strontium. 
Strontic Iodide , heated on platinum wire in the Bunsen flame, gives the spectrum in 
the red, so well represented in Bunsen’s and Kirchhoff’s drawing, and the great blue 
line 4607-5 of the metal. 
Strontic Bromide behaves much as the iodide does, but shows more of the structure 
in the red. 4607-5 is also always present, and is very bright, a considerable change from 
its appearance in the iodide, in the spectrum of which it is for a time faint and then 
becomes brighter. 
Strontic Chloride gives the bands very brightly at first, but not so brightly after a 
time ; 4607-5 is fainter, but is very distinct. 
