of the Vapours of Inorganic Salts. 59 1 



400° C. by means of an electric furnace. The quantity of 



each substance used was *005 gram, and it is therefore seen 



that the cadmium was in excess. The experiments with 



pure metallic cadmium previously referred to show that at 



1000° C. only light of shorter wave-length than X 3000 was 



. . . . 



completely absorbed, and in the cadmium-iodide experiments 



the amount of free cadmium was only ^ that employed in 

 the experiments on the absorption spectrum of cadmium 

 vapour. As the temperature of the furnace was raised, the 

 light after passing through the quartz tube was reddish in 

 colour, and when examined with the spectroscope showed 

 the ordinary absorption spectrum of iodine vapour. This 

 colour, however, completely disappeared when the tempera- 

 ture of the furnace was approximately 400° C, showing that 

 the iodine had combined with the cadmium. A large 

 number of photographs were then taken at temperatures 

 ranging from 400° C. to 1000° 0., and it was found that 

 cadmium-iodide vapour showed a decided general absorption 

 in the ultra-violet. At 400° C. there was scarcely any 

 evidence of absorption, as the light from the positive pole of 

 the electric arc could be photographed in the ultra-violet as 

 far as \2500. When, however, the temperature of the 

 furnace had reached 650° C. all light of shorter wave-length 

 than X 3500 had been absorbed, and this absorption spread 

 towards the red end of the spectrum as the temperature was 

 raised to 1000° C, so that absorption could then be traced as 

 far as X3800. As cadmium vapour w^as present in these 

 experiments, it would be expected that the X 3261 cadmium 

 absorption line would be visible on the photographs, but 

 owing to the great absorption of the iodide, this line could 

 only be seen faintly on one of the films taken, when the 

 temperature of the furnace was 580° C. Even at this com- 

 paratively low temperature the wave-length of the line 

 (A 3261) was near the limit of transmission. 



Finally, the absorption of light by cadmium-chloride 

 vapour was studied. This substance melts at 530° C. and 

 boils at 900° 0., and the absorption spectrum of its vapour 

 was photographed at temperatures ranging from 600° C. to 

 1000° 0. In these experiments the quartz tube was evacuated 

 to a pressure of *01 mm. of mercury, and the quantities of 

 the chloride used in two sets of experiments were '07 and 

 *045 gram respectively. It was evident from the results of 

 the first series of experiments that the cadmium-chloride 

 vapour had been partially decomposed at high temperatures, 

 for the 3261 line of cadmium appeared w r ith increasing 



