GASEOUS SPECTRA IN VACUUM TUBES. 101 
ing fogged with brown colouring matter deposited on the inside, and finally the 
spectroscope showed that the carbon bands in its spectrum were disappearing, 
and various unknown and isolated lines were appearing instead, together with 
a growth or increase of Hydrogen manifestations. 
Some of the new lines could be made to disappear momentarily by 
introducing a Leyden jar into the circuit, and were supposed therefore to 
belong to the compound gas Cyanogen; but others could not be made so to 
disappear, and they proved to be the low temperature Hydrogen lines. Again, 
under special management of the condensed spark, the tube would for a short 
time blaze up vividly, and exquisite lines were then seen, thinner, sharper, and 
brighter than anything previous,—and they, from their places and relative 
intensities, must have been a part of the eacelsior line-spectrum of Nitrogen. 
Several of these changes are noted in Appendix I.; where two separate 
tables refer really to one and the same Cyanogen tube, but with a consider- 
able interval of time between them; and another refers to a second tube of 
Cyanogen furnished to me by the maker on the same occasion as the first, but 
differing thus curiously in its spectrum ; viz., that while the first, in its earlier 
days, showed Nitrogen bands preponderating over those of Carbon, the second 
showed Carbon bands preponderating over Nitrogen; but both of them were 
remarkable then for little or no hydrogen indications. 
The next tube to heat up, to change its light from white to pink, and to 
alter its spectrum, was Hydro-chloric acid. It had begun with chlorine lines 
brilliantly, some Hydrogen lines and faint Carbon bands. These last are now 
gone completely ; also, or even more signally, every one of the chlorine lines 
absolutely ; but the Hydrogen lines are all increased, and to such a degree as 
to compete with a pure Hydrogen tube for showing the Lavender as well as 
the other three principal and high temperature lines of Hydrogen, besides 
crowds of the new low temperature lines of that element. In fact I cannot 
distinguish its spectrum now from one of pure Hydrogen supplied by the 
maker as such ; but call its tube, for the sake of distinction without a difference, 
“the tube of artificial hydrogen.” 
The pure chlorine tube still shows its chlorine lines, but they are becoming 
fainter ; and carbon bands and hydrogen lines have appeared, making its 
spectrum look very like what that of the Hydro-chloric acid was at first. 
Another tube that heats unduly, as if inclined for a change, and has much 
deposited haze in its interior, is Iodine: but no perceptible alteration of 
spectrum has yet been noted ; and because, perhaps, the maker put so large a 
quantity of solid iodine inside, that there is no chance of its all being dissociated, 
or converted into something else by my weak, small sparks, within any'moderate 
length of time ;--if Iodine is really, as some persons are beginning to suspect, 
not the elementary body which the chemists believe, but a compound. 
VOL. XXX. PART I. Q 
