2g8 



THE ALUMNI JOURNAL. 



quantity of gas into the main tube, and 

 again observing the spectra at the two 

 electrodes. 



A tube was filled with hydrogen and 

 showed no trace of the chlorine spectra; 

 a very small quantity of chlorine was 

 then let in through the side tube (in per- 

 forming this experiment it is necessary to 

 be careful that only a very small quantity 

 of chlorine be introduced). After the dis- 

 charge had been running through the 

 tube for a short time, the chlorine spec- 

 trum was found to be bright at the posi- 

 tive electrode, though no trace of it could 

 be detected at the negative. When the 

 discharge was kept on for some time, the 

 chlorine spectrum, though still visible at 

 the positive electrode, got fainter; it did 

 not appear at all at the negative. If a 

 considerable quantity of chlorine was 

 visible at both electrodes, though it was 

 brighter at the positive than at the nega- 

 tive. 



When the induction coil was reversed, 

 so that what was before the positive elec- 

 trode became the negative, the first effect 

 observed was that the chlorine spectrum 

 flashed out with great brilliancy at the 

 old positive electrode, and was very much 

 brighter than at 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 is ap- 

 parently no limit to the number of times 

 this effect may be obtained; at any rate, I 

 have driven the chlorine from the 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 vapor of brom- 

 ine was introduced into the tube instead 

 of chlorine. When, however, the capil- 

 lary tube was filled with chlorine instead 

 of hydrogen, and a little vapor of brom- 

 ine 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 experi- 

 ments suggest that the two gases in the 

 tube combine, and that the compound 

 gas so formed, is split up into ions which 

 travel along the tube, when, however, it 

 is in combination with chlorine the brom- 

 ine is the positive ion and travels to the 

 negative electrode. 



Another experiment tried was to let a 

 little vapor of sodium into the middle of 

 a capillary tube filled with air at a low 

 pressure. To prevent the sodium vapor 

 condensing on the walls of the tube, the 

 whole was placed on a sand bath and the 

 temperature raised so high that no con- 

 densation took place. After the dis- 

 charge had run through the tube for 

 about two hours the sand was removed 

 from the tube, and the movement of the 

 sodium vapor to the negative electrode 

 was very apparent even without using a 

 spectroscope, as there was a great patch 

 of yellow light near the negative elec- 

 trode 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 some- 

 what troublesome one, as it is exceed- 

 ingly difficult to get these very fine capil- 

 lary tubes so dry that the spectrum of the 

 discharge does not show the hydrogen 

 lines even before the hydrogen is intro- 

 duced into the middle of the tube; indeed, 

 I never succeeded in getting rid of the 



