IN CONNEXION WITH THE SPECTRUM OE THE SUN. 
645 
Strontic Fluoride refused to give any trace either of the strontium or compound spec- 
trum ; it is, in fact, only capable of being heated to a white heat and giving a continuous 
spectrum. 
Conclusions. 
It is to be observed, then, that when the spectra before referred to produced by flames 
are compared with those produced by the low-tension spark, the spectra of the metals 
in the combination are in the former case invariably more simple than in the latter, and 
that they are simplified to such an extent that only the very longest line is left ; thus: — 
Baric Iodide with the low-tension spark gives five and twenty lines. In the flame it 
gives but one, and that the longest, namely 5534*5. 
Baric Bromide gives five and twenty lines with the spark ; only one in the flame, the 
same longest line 5534*5. 
Baric Chloride five and twenty lines in spark and one, 5534*5, in flame. 
Baric Fluoride four lines in spark, 5534*5 alone in flame. 
Again, taking the case of strontium, we find that in the case of strontic iodide thirty- 
two lines are observed in the spark, one alone in the flame, and that is the longest, 
namely 4607*5, a line by far the longest in the spectrum of strontium. 
Strontic Bromide gives also thirty-two lines in the spark and but one in the flame, the 
same longest line 4607*5. 
Strontic Chloride gives thirty-two lines in the spark, but only this one, 4607*5, in the 
flame. 
Strontic Fluoride gives fourteen lines in the spark, but in the flame does not even give 
the longest line. There is, in fact, no spectrum at all due either to the metal or the 
compound. 
It is especially to be remarked that strontic oxide furnishes us with an intermediate 
condition of things between the chloride and fluoride. 
In this compound the hand near D is the only representative of the spectrum of the 
compound. The longest metallic line, 4607*5, is also invisible. We are justified, there- 
fore, in assuming that only a small quantity of the undissociated compound is present in 
the reaction. 
Experiments to determine the cause of the similarity of the spectra of the various salts 
observed in air. 
It was noticed in the earliest observations of the spectra of salts in the spark that 
after a time the spectrum was nearly the same, whatever salt had been placed in the cup. 
I therefore determined upon a careful study of the phenomena when the salt was 
submitted to the heat of the ordinary Bunsen flame; and after some preliminary obser- 
vations, I requested Mr. Friswell to make a detailed examination of the various stages 
of the reactions in question. I now append his observations, which, taken in connexion 
with the other branches of the inquiry, clearly establish that the band spectrum is that 
of the oxide. 
