614 



Scientific Proceedings^ Royal Dublin Society. 



only to X 3600. The effect of self-induction is to eliminate some lines 

 altogether, and to cause others to become discontinuous. The absorption 

 band is in the visible region, so that with chlorine, bromine, and iodine 

 the absorption seems to move along the spectrum tovk^ards the red end 

 with increase in the atomic weight of the element examined. 



Principal Lines of Iodine. 



Hydrogen. 



Hydrogen was prepared from zinc and sulphuric acid. In order to 

 purify the gas, it was passed through tubes containing : — 



(1.) Pumice moistened with lead acetate solution, to remove sulphuretted 

 hydrogen. 



(2.) Pumice moistened with silver sulphate to remove arsenic or 

 phosphorus. 



(3.) Solid potassium hydroxide, to remove sulphur dioxide. 



(4.) Pumice moistened with sulphuric acid, 



(5.) Sulphuric acid alone, 



Hydrogen was the only non-metallic element examined by Schuster and 

 Hemsalech. They noticed that if there were enough self-induction the 

 hydrogen lines could be obtained almost as sharp as those of the vacuum 

 tube spectra of that element. In my photographs self-induction makes the 

 lines sharper, but at the same time it causes the elimination of the lines 

 due to the electrodes. This is especially so when gold is sparked in 



to remove moisture. 



