642 
ME. J. NOEMAN LOCKYEE ON SPECTEUM-ANALYSIS 
Table. The fact may then be simply stated, that in the case of lead the complexity of 
the spectrum increases as the atomic weight of the non-metallic element with which it 
is combined decreases. 
Barium. 
The next metal experimented on w T as barium, an element of much lower atomic weight 
than lead, and in this respect occupying a position not very much above the mean atomic 
weight of the elements. It was soon found that the facts observed with lead did not 
completely hold with regard to barium, although they include the phenomena presented 
by the chloride, bromide, and iodide. Even with these salts, however, the phenomena, 
though the same in kind, differ somewhat in degree. For instance, the same number of 
metallic lines was observed in all these salts, and between the appearance of the chloride 
and the bromide spectrum there was no appreciable difference. In the case of the 
iodide, however, there was a sensible change in the direction expected from the behaviour 
of lead — i. e. the spectrum became dimmer, that is, exhibited a tendency to die out. 
When, however, baric fluoride was examined, a different state of things was observed. 
Instead of the spectrum becoming more complex it became simpler, exhibiting in fact 
only the four longest lines of barium with any degree of distinctness, and these showing 
but little brilliancy. 
Strontium and Magnesium. 
Strontium behaved in this particular in the same way as barium did, the falling off of 
the lines in the fluoride being very marked. In the case of magnesium (which, as regards 
its chloride, bromide, and iodide, followed the behaviour of the alkali metals, to which I 
shall immediately refer, rather than that of barium and strontium), the fluoride exhi- 
bited the same stubborn resistance to the action of the spark. It is to be remarked that 
these three fluorides are non-volatile, and so infusible that even after long exposure to 
the current there was little or no indication of coherence ; in fact, in the case of mag- 
nesic fluoride, the salt was distinctly seen to be blown out of the cup as a cloud of dust, 
and when one of these particles was converted into vapour in the spark, the spectrum 
exhibited fragments of lines sharp at both ends. 
On blowing a cloud of magnesic fluoride in fine powder through the spark, b in 
particular was seen as a series of three pointed lines. 
It will be seen from the above experiments, and from the annexed map of the strontium 
salts observed in air (Plate LI.) taken as a type of this group, that the general statement 
made for lead does not apply to barium or strontium, the chlorides, bromides, and iodides 
of which metals are pretty equally volatile, while their fluorides are apparently not readily 
volatile at any temperature which I could employ. 
Sodium. 
Sodium and lithium, elements of low atomic weight, were the next metals experimented 
upon. 
