of the Vapours of Inorganic Salts. 61 



which is much the more prominent, was found to broaden 

 perfectly symmetrically when pure Cd was examined, but 

 unsymmetrically when mercury was added. The o absorption 

 line at \ 2288*1 attained a width of about 200 A.U. at the 

 highest temperatures employed, but the A 3261 line was 

 never very broad under these conditions. In the present 

 experiments, only the absorption line at A 3261 could be 

 obtained, as the carbon arc which was the source of the 

 continuous spectrum is not suitable for the examination of 

 absorption lines in the neighbourhood of A2288'l. These 

 experiments on the absorption of the vapour were carried 

 out at different temperatures with each specimen of cadmium, 

 and the amounts of the metal used were '015 gram and 

 •065 gram respectively. The vapour obtained: from *015 

 gram of one specimen gave an absorption line at A 3261, 

 which broadened symmetrically with increase of temperature 

 until its width was about 100 A.U. at 1000° 0. At the 

 above temperature the vapour also gave additional absorption 

 lines in the region A, 3000-X 3200, and a general absorption 

 in the region A2500-X3000, which is possibly due to the 

 broadening of the X2288 line. These absorption lines were 

 the same as those previously obtained when the absorption 

 spectrum of Cd01 2 was examined, with the exception that 

 cadmium vapour gave an extra line at 3178. 



The vapour obtained from '065 gram of the other speci- 

 men gave practically the same absorption spectrum as the 

 above, with the difference that the absorption lines in the 

 region X 3000-A 3200 were very faint and difficult to detect 

 with certainty. It was found, however, that these lines could 

 be more readily obtained if cadmium vapour were mixed 

 with hydrogen. For this purpose hydrogen was allowed to 

 enter an evacuated quartz tube containing *03 gram of 

 cadmium until the pressure was 25 cm. of mercury. Photo- 

 graphs taken when the temperatures of the vapour were 880° 

 and 970° showed the presence of the absorption lines in the 

 region A 3000-A 3200. The wave-lengths of some of these 

 rather diffuse lines were measured, and the approximate 

 values obtained were 3142, 3152, 3162, and 3171 A.U. It 

 therefore follows that these lines cannot be attributed to 

 the vapour of CdUl 2 , and the experiments suggest that 

 they may possibly be due to an unstable compound of Cd 

 and H, the lines being produced w r hen the compound 

 dissociates. 



