MR. W. CROOKES ON THE SPECTRA OF ARGON. 2AT 
observations have already led both the discoverers to the same conclusion, that the 
gas argon is not a simple body, but is a mixture of at least two elements, one of 
which glows red and the other blue, each having its distinctive spectrum. The 
theory that it is a simple body has, however, support from the analogy of other gases. 
Thus, nitrogen has two distinct spectra, one or the other being produced by varying 
the pressure and intensity of the spark. I have made vacuum tubes containing 
rarefied nitrogen, which show either the fluted band or the sharp line spectrum by 
simply turning the screw of the make-and-break, exactly as the two spectra of argon 
can be changed from one to the other. 
The disappearance of the red glow and the appearance of the blue glow in argon as 
the exhaustion increases also resembles the disappearance of the red line of hydrogen 
when exhaustion is raised to a high point. PxLtcKer, who was the first to observe 
this occurrence, says:* “ When RuamKorrr’s small induction coil was discharged 
through a spectral tube enclosing hydrogen, which was gradually rarefied to the 
highest tenuity to be reached by means of GEISSLER’s exhauster, finally the beautiful 
red colour of the ignited gas became fainter, and passed gradually into an undetermined 
violet. When analysed by the prism, He (the red, C, line) disappeared, while H8 
(the green, F, line), though fainter, remained well defined. Accordingly, light of a 
greater length of wave was the first extinguished.” 
The line spectrum of nitrogen is not nearly so striking in brilliancy, number, 
or sharpness of lines as are those of argon, and careful scrutiny fails to show 
more than one or two apparent coincidences between lines in the two spectra. 
Between the spectra of argon and the band spectrum of nitrogen there are two or 
three close approximations of lines, but a projection on the screen of a magnified 
image of the two spectra partly superposed shows that two at least of these are not 
real coincidences. 
I have looked for indications of lines in the argon spectra corresponding to the 
corona line at 531°7, the aurora line at 557°1, and the helium line at 587°5, but have 
failed to detect any line of argon sutfticiently near these positions to fall within the 
limits of experimental error. 
I have found no other spectrum-giving gas or vapour yield spectra at all like those 
of argon, and the apparent coincidences in some of the lines, which on one or two 
occasions are noticed, have been very few; and would probably disappear on using a 
higher dispersion, Having once obtained a tube of argon giving the pure spectra, I 
can make no alteration in it, except that which takes place on varying the spark or 
increasing the exhaustion, when the two spectra change from one to the other. As 
far, therefore, as spectrum work can decide, the verdict must be that Lord RayLEeIcH 
and Professor Ramsay have added one, if not two, members to the family of 
elementary bodies. 
# On the Spectra of Ignited Gases and Vapours.” By Drs, Priicxer and Hurrrorr, ‘ Phil. Trans,,’ 
Part L., vol. 155, p. 21. 
