1866. | Physics. 119 
lysis have likewise been made by M. E. Diacon. Like Mitscherlich, 
he has studied the influence of the electro-negative elements on the 
spectra of metals, most of the researches hitherto communicated 
having been directed to the electro-positive elements only. ‘The 
method of analysis founded by Kirchhoff and Bunsen on spectrum 
observations has given results so remarkable that its utility im 
chemical researches is not to be contested. Nevertheless, the prin- 
ciple on which it rests is only true under certain determimed con- 
ditions. From the observations of the author and of M. Mitscherlich, 
it seems certain that the different compounds of a metal do not 
exhibit an identical spectrum, and in this paper M. Diacon has col- 
lected the experiments which show the influence of the electro- 
negative element on the radiations emitted by different salts of the 
same metal. From these experiments, which are far too numerous 
to admit of bemg given here in abstract, two consequences result :— 
1. The spectra given by Kirchhoff and Bunsen for those of the 
alkaline earthy metals being the appearances observed at the 
moment the salt is introduced into the flame, it follows that such 
spectra must be a mixture of the spectrum of the chlorides and of 
that of the metal; 2. The appearance of lines not belonging to 
the metal may be considered as a probable, if not a certain, indica- 
tion of the existence of a spectrum peculiar to the compound with 
which it is produced. Thus the study of the lnes produced by 
bromides, iodides, and fluorides in the gas flame may give valuable 
indications, and furnish new proofs of the existence of a special 
spectrum for binary compounds. All the metals do not lend them- 
selves with equal facility to these experiments. The best defined 
results are obtained with the alkaline earthy metals,and with copper 
and bismuth. 
The attentive study of the light emitted by the bromides, iodides, 
and fluorides demonstrates, then, that the introduction of those salts 
into a flame determines the appearance of lines which do not exist 
either in the spectrum of the metals or in that of the chloride. 
We must, therefore, conclude that these compounds, like the 
chloride, have peculiar spectra, the superposition of which on that 
of the metal gives the appearance observed in each of them. 
From the author’s experiments we learn that spectrum observa- 
tions give us the means of determining not only the metal but the 
electro-negative element combined with it. Unfortunately, very 
definite results are only obtamed with a few of these compounds. 
Although the spectra of the chloride and bromide of copper are 
very much alike, it is easy to distinguish one from the other, and 
there are differences in the two spectra easily to distinguish without 
haying recourse to measurement. Jor example, the position of the 
greenish blue lines is characteristic of the bromide, that of the 
violet lines for the chloride. When the two salts are placed in the 
