1883.] Absorption of Ultra-Violet Bays by various Substances. 71 



March 8, 1883. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read :— 



I. " Notes on the Absorption of Ultra- Violet Kays by various 

 Substances." By G. D. Liveing, M.A., F.R.S., Professor of 

 Chemistry, and J. Dewar, M.A., F.R.S., Jacksonian Pro- 

 fessor, University of Cambridge. Received March 1, 1883. 



The following notes contain some records of ultra-violet absorp- 

 tions in addition to those which have been examined by Soret, 

 Hartley, M. de Chardonnet, and other investigators. For these 

 observations we have generally used the spark of an induction coil, 

 with Leyden jar, between iron electrodes as the source of light. 

 Occasionally we have used other electrodes, but the lines of iron are 

 so multitudinous, and so closely set in a large part of the ultra- 

 violet region of the spectrum, that they form almost a continuous 

 spectrum, at the same time there are amongst them a sufficient 

 number of breaks and conspicuous lines to serve as points of 

 reference. The spectroscope has a single prism of quartz, and the 

 telescopes have quartz lenses. The image of the spark was projected 

 on to the slit of the spectroscope by a quartz lens, and the absorbent 

 substances were interposed between the slit and the last-mentioned 

 lens. The gases were held in tubes fitted, some with quartz, others 

 with rock salt, plates on the ends ; liquids in cells with quartz sides. 

 The spectra were all photographed. 



Chlorine in small quantity shows a single absorption band extend- 

 ing from about N (3580) to T (3020). As the quantity of chlorine 

 is increased this band widens, expanding on both sides, but rather 

 more rapidly on the less refrangible side. Different quantities of 

 chlorine produced absorption from about H (3968) to wave-length 

 2755, from wave-length 4415 to 2665, and from wave-length 4650 to 

 2630. With the greatest quantity of chlorine tried the absorption did 

 not extend above wave-length 2550. 



Bromine vapour in small quantity absorbs light up to about L 

 (3820), and is quite transparent above that. With larger quantity 



