1895.] On the Electrolysis of Gases. 247 



quantity of chlorine was introduced through the side tube, the chlo- 

 rine spectrum was visible at both electrodes, though it was brighter 

 at the positive than at the negative. 



When the induction coil was reversed, so that what was before the 

 positive electrode became the negative, the first effect observed was 

 that the chlorine spectrum flashed out with great brilliancy at the 

 old positive electrode, and was much brighter than at any previous 

 period. This, however, only lasted for a second or two ; the chlorine 

 spectrum rapidly faded away and for a time was not visible at either 

 electrode. Soon, however, the chlorine spectrum appeared at the 

 new positive electrode, having thus been transferred from one end of 

 the tube to the other. 



On again reversing the coil the same phenomenon was repeated. 

 There was apparently no limit to the number of times this effect may 

 be obtained ; at any rate, I have driven the chlorine from one end of 

 a tube to the other 14 times in succession by reversing the coil. The 

 chlorine is always driven to the positive electrode, showing that the 

 chlorine ion carries a charge of negative electricity. The same 

 effect was obtained when a little vapour of bromine was introduced 

 into the tube instead of chlorine. When, however, the capillary tube 

 was filled with chlorine instead of hydrogen, and a little vapour of 

 bromine let into the tube, the bromine went to the negative electrode 

 instead of to the positive, as it did when introduced into the hydrogen 

 tube. These experiments suggest that the two gases in the tube com- 

 bine, and that the compound gas so formed is split up into ions which 

 travel along the tube ; that bromine when in combination with hydro- 

 gen is the negative ion, and therefore travels to the positive elec- 

 trode ; when, however, it is in combination with chlorine the bromine 

 is the positive ion and travels to the negative electrode. 



Another experiment tried was to let a little vapour of sodium into 

 the middle of a capillary tube filled with air at a low pressure. To 

 prevent the sodium vapour condensing on the walls of the tube, the 

 whole tube was placed on a sand-bath and the temperature raised so 

 high that no condensation took place. After the discharge had run 

 through the tube for about two hours the sand was removed from the 

 tube, and the movement of the sodium vapour to the negative elec- 

 trode was very apparent even without using a spectroscope, as there 

 was a great patch of yellow light near the negative electrode and 

 none in any other part of the tube. 



Another experiment was to introduce a small quantity of hydrogen 

 into a tube filled with air at a low pressure : the hydrogen made its 

 way to the negative electrode. This experiment is a somewhat trouble- 

 some one, as it is exceedingly difficult to get these very fine capillary 

 tubes so dry that the spectrum of the discharge does not show the 

 hydrogen lines even before the hydrogen is introduced into the middle 



