LUEDEKING — ELECTRIC DISCHARGE ON IODINE. 447 . 



peared, and that what was left was nitrogen. This result is con- 

 trary to what we should expect had hydrogen been formed by 

 dissociation of the iodine. The confined gases would have been 

 under a pressure. 



The contents of the tube were thoroughly extracted by wa- 

 ter, the solution so obtained made slightly alkaline, and sulphu- 

 retted hydrogen passed to saturation. After expulsion of the 

 gas and slightly acidifying with nitric acid, nitrate of silver was 

 added, and the precipitate filtered, washed, dried and weighed. 

 The quantity of precipitate produced was nearly equal to what 

 theory requires for iodide of silver ; it weighed 0.061 grm. 



Evidently, then, in my experiment the disappearance of the ele- 

 ment iodine was not due to any other cause than its uniting with 

 the constituents of the glass. Under the influence of the electric 

 discharge iodine certainly acquires superior chemical affinities, 

 attacking the substance of the glass and forming iodides, and, 

 from the disappearance of one-fifth of the volume of gas, I should 

 say, also some iodates. To meet this eventuality, I reduced bv 

 sulphuretted hydrogen previous to precipitation. 



The changed brilliancy of the spectral hydrogen lines that 

 Mr. Smyth observed must, then, it seems to me, be attributed to 

 another cause than a generation of hydrogen by a decomposition 

 of iodine. First of all, it is certain that the changed condition of 

 the tension in the tube has something to do with it. 



I determined to decide the matter experimentally. An excess 

 of iodine was sealed up in the same kind of tube that I used 

 above. On passing the discharge at the ordinary temperature, 

 only faint indications of hydrogen were observed in the spectro- 

 scope. The tube was then heated gently, so that a great part 

 of the iodine was volatilized. As the temperature rose, and the 

 iodine vapor became more and more dense, to my surprise the 

 hydrogen blazed in the spectrum with remarkable brilliancy. On 

 cooling, the spectrum slowly changed back to its original appear- 

 ance ; hydrogen was again only faintly perceptible. It was clear 

 then why the hydrogen lines in Mr. Smyth's tube should become 

 so brilliant after the disappearance of the iodine. This latter is 

 capable of binding hydriodic acid, which is the form in which 

 the hydrogen is introduced into the tube. When by the process 



