Optical Properties of Niobium

The refractive index of niobium is 1.80, the coefficient of absorption 2.11, and the reflexion capacity 41.3 per cent, when measured with yellow light of wave-length λ = 5790.

The arc spectrum of niobium has been measured in the region λ = 2600 to λ=6000, using specimens of the pentoxide obtained from several niobium ores and a concave grating of 6 feet focus. The more intense lines are tabulated in the following table:

Arc spectrum of Niobium

Wave-length.	Relative Intensity of Line.
2618.5	8
2766.5	10
2824.5	8
2868.6	8
2883.2	8
2961.3	10
2990.4	10
3010.9	10
3036.2	10
3039.8	10
3063.5	10
3094.3	10
3108.7	8
3130.9	8
3163.5	8
3225.6	8
3247.7	10
3274.1	10
3358.5	8
3498.7	8
3554.8	9
3563.7	10
3576.0	8
3580.4	10
3664.8	8
3698.0	8
3713.2	8
3726.4	8
3740.0	8
3759.7	10
3781.2	8
3787.3	8
3791.4	8
3798.2	8
3810.6	8
3825.0	8
3894.2	9
3914.9	8
3937.7	8
3966.4	8
4022.9	10
4032.7	10
4059.1	10
4079.9	10
4101.1	10
4124.0	10
4130.1	8
4137.3	10
4139.9	10
4152.8	10
4163.8	8
4164.9	8
4168.3	10
4191.1	10
4192.2	8
4218.1	8
4229.3	8
4262.2	8
4275.3	10
4299.8	10
4301.3	10
4311.5	8
4321.6	8
4336.6	8
4349.2	8
4351.8	10
4378.2	8
4437.5	9
4447.5	8
4523.6	10
4547.0	8
4564.7	10
4573.3	8
4579.6	8
4581.8	8
4587.2	8
4664.0	8
4667.5	10
5079.1	8
5195.4	8
5664.9	8
5665.8	8
5671.2	10
5838.8	8
5900.7	10
6661.1	10
6677.5	8

The arc and spark spectra in the ultraviolet region have also been photographed and measured. The spectral structure of niobium resembles that of vanadium, and various regularities have been discovered in it. In order to be able to establish spectrographically the presence of traces of a foreign element in a substance, de Gramont determined which of the lines in the spectrum produced by a condensed spark discharge are the last to appear as the quantity of foreign element is gradually reduced. These are not necessarily the most intense lines in the arc or spark spectrum. The wave-lengths of the ultimate lines given by niobium in this manner with a crown Uviol glass spectrograph are: 4101.0, 4079.7, 4059.0, 3358.4, in Angstrom units.

Eder and Valenta have measured a large number of lines in the flame spectrum given by niobium pentoxide between carbon electrodes. The flame spectrum of niobium between carbon electrodes consists of a blue cone with a yellowish-green shell. The band spectrum of niobium is composed of a very large number of lines which are comparatively sharp but not strong.

The X-ray spectra of niobium have been investigated. Aston was unable to obtain a definite mass spectrum of the metal. The arrangement of the electron groups in the atom has been considered by. Lessheim and Samuel. Niobium is not radioactive.