72 



Profs. G. D. Liveiug and J. Dewar. [Mar. 8, 



the absorption increases, gradually extending with increase of 

 bromine vapour from L to P (3360) ; and at the same time there is a 

 gradually increasing general absorption at the most refrangible end 

 of the spectrum beginning at about wave-length 2500 ; so that the 

 denser bromine vapour is transparent for a band between wave- 

 length 2500 and 3350. ' 



Liquid bromine in very thin film between two quartz plates is 

 transparent for a band between wave-length about 3650 and 3400, 

 shading away on both sides, so that below M on one side and above P 

 on the other the absorption seems complete. The transparency of the 

 liquid film ends on the more refrangible side just where that of the 

 vapour begins. 



Iodine vapour tolerably dense cuts off all within the range of our 

 photographs below wave-length 4300, and its absorption gradually 

 diminishes from that point up to about wave-length 4080, from that 

 point it is transparent.* Denser vapour produces complete absorption 

 up to 4080 and partial absorption above that point. 



Iodine dissolved in carbon disulphide is transparent for a band 

 between Gr and H, cutting off all above and below. It is not possible to 

 tell how much of the light above M (3727) is absorbed by iodine in 

 such a solution, inasmuch as carbon disulphide is opaque for rays 

 more refrangible than M. 



Iodine dissolved in carbon tetrachloride when the solution is 

 weak, shows only the absorption due to the solvent, described below. 

 More iodine increases the absorption until it is complete above P 

 (3360), with shading edge as far down as about wave-length 3400. 



Snlphurous acid gas produces an absorption band which is very 

 marked between II (3179) and wave-length 2630, and a fainter 

 absorption extending on the less refrangible side to O (3440), and on 

 the other side to the end of the range photographed, wave-length 

 2300. 



Sulphuretted hydrogen produces complete absorption above wave- 

 length 2580. Below that a partial general absorption. 



Vapour of carbon disulphide in very small quantity produces an 

 absorption band extending from P to T, shading away at each end ; 

 no absorption in the higher region. With more vapour the absorption 

 band widens, extending from about wave-length 3400 to 3000, and a 

 second absorption occurs beginning at about wave-length 2580, and 

 extending to the end of the range photographed. 



Carbon tetrachloride liquid produces an absorption band with a 

 maximum about R, extending, but with decreasing intensity, up to 



* The principal absorption band of the haloids seems to shift towards the less 

 refrangible side with increase of atomic weight, and so to agree with the general 

 rule which Lecoq de Boisbaadran has noticed in the shifting of corresponding lines 

 in the spectra of groups of similar metals. — March 16. 



