The continuous absorption of light in potassium vapour

Abstract

While considerable attention has been paid to the line and band absorption of the alkali metals, very little work has been done on the continuous absorption. R. W. Wood and Holtzmark have observed the existence of this absorption, and Harrison has made some measurements on the continuous absorption of sodium in the region 2500 Å. U. - 2150 Å. U. In the present paper, results are given for potassium over a wide range of wave-length (4000 Å. U. - 2200 Å. U.) and under widely different experimental conditions. The ordinary methods of spectrophotometry have usually been designed to measure the absorption of solutions, etc., and are not suitable for measuring the absorption in a vapour unless the vapour pressure can be kept absolutely constant. A method of spectrophotometry has been developed by which it is possible to obtain measurements of the relative absorption coefficients for different wave-lengths correct to about 2 per cent, without keeping the vapour pressure absolutely constant. While the method is specially suitable for the measurement of an absorption which is not quite steady, it is really of quite general application.