LXVIII. Absorption of light by vapours of Pb, Sn, Si, Sb, and Mg

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Abstract
Absorption of light by non-luminous vapours of Pb, Sn, Bi, Sb, and Mg has been studied, and it has been found that the absorption spectrum of lead shows, besides the fundamental line λ 2833, a banded spectrum at about 1100° C., degraded towards the red and spaced at intervals of 32 Å.U. nearly. Absorption spectrum of tin showed only a faint reversal of λ 2706·6. That of bismuth showed, besides λ 3067, 2524, 2276, and 2230 & 28, a typical banded spectrum containing about 20 bands. The absorption at each of these bands is very diffuse and complex, consisting of a number of finer bands. With increase of vapour density all these bands gradually fuse together (beginning from the short wave-length side) to form a region of continuous absorption. At about 1200° C. another typical banded spectrum appeared in the visible region extending from λ 6500 to λ 4500. The absorption spectrum of antimony showed fine lines at 2312 and 2306 and a handed spectrum extending from λ 2305 to λ 2250, while at higher temperatures there was another banded spectrum in the region 2830→3000 and a fine line at λ 2770. The existence of the banded spectra in the case of these metals of the higher groups of the periodic table leads us to the conclusion that the molecules of these elements are polyatomic. λ 4571, the single line spectrum of magnesium, has been for the first time photographed as an absorption-line by using a long column of the vapour.

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