Uranium Spectrum

Compounds of uranium do not colour a non-luminous flame. The emission spectrum is exceptionally rich in lines, which, however, are not in any way characteristic, and the detection of small quantities of uranium spectroscopically is practically impossible. Exner and Haschek enumerated in the arc spectrum 4940 lines between the wave-lengths (Angstrom units) 2263.5 and 6827.2, few of which were of marked intensity, while Kiess and Meggers have distinguished 680 lines in the yellow, red, and infra-red, up to a wave-length of 9530 Å. Measurements have been made of the wave-lengths of the lines in the spark, arc, absorption, fluorescence and phosphorescence, and high-frequency spectra.

Pollok has investigated the spark spectrum of a solution of uranium chloride, with a view to determining the most persistent lines, and records his results as follows:

Wave-length.	Intensity and Persistency.	Wave-length.	Intensity and Persistency.	Wave-length.	Intensity and Persistency.
4605.4	4 φ	3693.9	2 χ	2969.6	1 φ
4603.9	φ	3672.7	2 ψ	2941.9	2 χ
4543.8	7 φ	3552.4	2 ψ	2888.3	1''' φ
4415.4	2 φ	3453.7	2 φ	2865.7	2 χ
4371.9	2 φ	3436.9	2 φ	2828.1	1 φ
4355.8	4 φ	3337.9	2 χ	2794.0	2 χ
4341.9	4 φ	3270.3	2 φ	2790.8	1 φ
4241.9	4 ψ	3244.4	2 φ	2766.0	1 φ
4171.8	3 φ	3093.1	2 χ	2763.0	1 φ
4090.3	4 χ	3072.9	2 φ	2742.7	1 φ
3979.9	2 φ	3058.0	2 χ	2733.4	1 φ
3954.9	2 χ	3044.3	2 χ	2635.6	2 χ
3874.2	2 φ	3006.9	1 φ	2552.5	1 φ
3859.7	2 φ	2974.2	1 φ	2549.5	1 φ
3783.0	2 φ	2971.2	2 φ

Exner and Haschek (loc. cit.) record the following as the most intense lines in the arc and spark spectra of uranium.

Arc Uranium Spectrum

Wave-length.	Intensity.
3932.19	5
4090.26	5
4171.74	5
4341.83	5
4355.82	5
5493.15	10
5528.01	10
5915.61	8
6395.68	8
6449.38	10

Spark Uranium Spectrum

Wave-length.	Intensity.
4090.28	4
4241.88	4
4269.84	4
4341.89	4
4355.89	4
4472.55	6
4515.50	4
4543.79	7
4545.76	4
4555.30	4
4603.86	4
4627.26	5
4646.80	4
4689.28	4
5493.16	4
5528.02	4

Owing to the fact that 75 per cent, of the principal uranium lines are absent from the solar spectrum, it has been suggested that this element is probably absent from the sun, but Meyer has shown that in presence of other metals the emission spectrum of uranium is invisible, unless the latter element is present in considerable concentration, usually about 7 per cent., and this worker therefore suggests that the absence of uranium lines in the solar spectrum is due to the presence of relatively large quantities of iron.