Optical Properties of Tantalum

The refractive index of tantalum is 2.05, the coefficient of absorption 2.31, and the reflexion capacity 43.8 per cent, when measured with yellow light of wave-length λ = 5790. The spectral emissivity and the radiation intensity and their variation with temperature have been measured by Worthing. For a comparison of the radiation constants of tantalum, platinum, osmium and carbon, see the references cited. The flame spectrum of tantalum between carbon electrodes consists of a blue cone with a reddish-yellow edge.

The strongest lines in the arc spectrum of tantalum from wave-length 7000 Å to wave-length 3000 Å, and their relative intensities, are set out in the table.

The spark spectrum of tantalum has been examined from wave-length 4700 A to wave length 2180 Å. The strongest lines and their relative intensities are set out in the table.

The visible portion of the spark spectrum between tantalum electrodes is very weak, and the individual lines are measurable only with difficulty. The lines between λ = 2000 and λ = 4700 in the spectrum of the spark discharge under water are the same as in air, unlike most other metals.

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 disappear as the quantity of foreign element is gradually reduced. The ultimate lines given by tantalum in this manner have the following wave-lengths, expressed in Angstrom units: (a) In the visible region, 6045.5 and 5997.4; (b) using a crown Uviol spectrograph, 3631.9, 3406.9, 3318.8, 3311.2; (c) using a quartz spectrograph, 2963.3.

Arc spectrum of Tantalum

Wave-length.	Relative Intensity of Line.
6675.7	9
6621.4	9
6612.1	9
6575.1	9
6516.3	10
6514.5	9
6505.7	9
6485.6	10
6450.5	10
6430.9	10
6428.8	6
6389.6	10
6361.0	9
6356.3	9
6325.2	9
6309.7	10
6268.8	10
6256.8	10
6154.7	5
6047.4	5
6045.6	5
5997.4	6
5944.2	5
5939.9	5
5877.6	5
5811.2	6
5780.8	5
5776.9	5
5665.0	8
4574.5	5
4566.0	4
4552.1	4
4531 0	5
4511.1	10
4486.2	4
4415.9	4
4386.2	4
4279.2	4
4206.0	10
4181.3	4
4178.0	4
4148.0	5
4136.3	5
4129.5	5
4105.2	4
4068.0	6
4064.7	5
4061.5	5
4027.0	5
3999.4	4
3996.3	4
3821.9	10
3642.2	10
3626.8	9
3607.5	7
3511.2	8
3497.9	5
3480.7	5
3463.9	4
3407.1	4
3371.6	5
3358.6	4
3318.9	5
3311.3	9
3223.9	4
3181.0	4
3103.4	4
3069.3	4

Spark spectrum of Tantalum

Wave-length.	Relative Intensity of Line.
4607.0	5
4205.5	5
4191.1	6
4168.3	8
4164.8	8
4163.8	8
4137.3	7
4124.0	10
4101.1	10
4079.9	12
4059.1	15
4032.7	5
3966.4	5
3905.8	10
3832.0	6
3819.0	5
3803.1	5
3798.3	6
3791.4	6
3787.2	5
3742.6	5
3726.4	5
3717.3	8
3713.2	6
3688.2	5
3683.7	8
3659.7	6
3651.3	6
3580.5	6
3576.0	5
3535.5	6
3432.9	5
3225.6	5

The X-ray spectra of tantalum have been investigated. The emission of electrons from tantalum when heated to high temperatures has received considerable investigation. Electron emission from the cold metal has been studied by Rother, and the arrangement of electron groups in the atom by Lessheim and Samuel. Tantalum is not radioactive.