OF SOME OF THE CHEMICAL ELEMENTS. 
147 
be closely approximated in position to, but a little more refrangible than, a similar 
pair of nitrogen lines. 
In air these four lines would form an ill-defined double line, while in oxygen the 
exaltation in brilliancy of the lines due to oxygen would make up for the extinction of 
those of nitrogen, thus leaving a pair similar to that seen in air, but now a little more 
refrangible, from the loss of the less refrangible line of nitrogen, and the greater bright- 
ness of the faint and more refrangible of the oxygen lines. This explanation exactly 
corresponds with the changes in appearance and position of the double line. The obser- 
vations have been repeated several times with oxygen from chlorate of potash, and also 
with oxygen from bichromate of potash and sulphuric acid. The change in position as 
observed relatively to the corresponding air line in the spectrum of comparison was not 
relied upon. The fixed cross of the micrometer was made to coincide with the oxygen 
line next in less refrangibility, 2626, the moveable cross was then brought upon the 
centre of the brighter of the pair 2642. When a current of pure oxygen was made to 
pass through the glass tube in which the platinum electrodes were sealed, the double 
line was seen to have moved from the point of intersection of the wires towards the 
more refrangible end of the spectrum. To restore the cross to a position similar to that 
which it before occupied, namely, upon the centre nearly of the brighter of the pair of 
lines, required that the screw skould be turned through a part of a revolution corre- 
sponding to a little more than two units of the scale. This measure is greater than 
the apparent change in position would have suggested, for in oxygen the lines are rather 
broader and more nebulous. The distance between the components of the double line 
is greater in oxygen. The alterations of position and of character are much better seen 
when the spectra of oxygen and nitrogen are viewed simultaneously. 
A similar explanation is to be given of the nebulous band in the red at 807. In 
oxygen the position of greatest brightness is more refrangible than it is in air and in 
nitrogen, though the band itself does not advance beyond the more refrangible limit of 
the corresponding band in air. The line at 629-5 is a pure nitrogen one and fades out 
completely in oxygen, but then a nebulous line appears at a little distance, about 638. 
Of this, in the air-spectrum, a faint trace only can be perceived. — Feb. 1864.] 
10. Sodium ,. — When the spark was passed between electrodes of sodium, in addition 
to the well-known double line, three other pairs of lines and a nebulous band made 
then- appearance in the spectrum. The two more prominent of these are not far from 
air lines, and with an instrument of insufficient dispersive power might easily be con- 
founded with them. As these lines might be occasioned by impurities in the com- 
mercial sodium employed, I prepared an amalgam of sodium, by making mercury the 
negative electrode in a solution of pure chloride of sodium. The mercury had been 
examined, and its spectrum was known. When the spark passed between this amalgam 
and a platinum wire, the same lines were seen, with their peculiar characteristics of 
relative position and intensity. Cotton moistened with solutions of chloride of sodium 
and of nitrate of soda was then used as one electrode, the other being a platinum wire. 
mdccclxiv. x 
