THE ALUMNI JOURNAL. 



297 



the cathode gets distinctly red, whilst that 

 next the anode gets green; this difference 

 in the color at the ends of the tube goes 

 on increasing until the tube presents a 

 most striking appearance, the part near 

 the cathode being bright red, while that 

 near the anode is a bright green. The 

 difference in color attains a maximum 

 value, and if the discharge is allowed to 

 run for several hours, the contrast be- 

 tween the two ends disappears to a very 

 great extent; the discharge throughout 

 the whole of the tube being pinkish and 

 apparently passing mainly through hy- 

 drogen. This is doubtless due to the 

 diffusion through the tube of the hydro- 

 gen, which in the early stagts of the dis- 

 charge had accumulated about the cath- 

 ode; one advantage of using very narrow 

 tubes in that with them this diffusion is 

 slow. When the tube is in this condi- 

 tion the color of the discharge sometimes 

 changes suddenly, and for a second or 

 two is green instead of pink, showing that 

 though in the main the discharge passes 

 through hydrogen, it occasionally leaves 

 the hydrogen and passes through the 

 chlorine. This transference of the dis- 

 charge from one constituent to another 

 of a mixture of gases is not infrequently 

 observed when the gases are mixed in 

 certain proportions. 



Some of these capillary tubes showed 

 after the discharge had been passing 

 through them for some time a peculiar 

 patchy appearance, some portions of the 

 tube being a much brighter red than 

 others, while other portions were green. 

 In some tubes this occurred to such an 

 extent that the discharge showed an ir- 

 regularly striated appearance. This 

 effect is due, I believe, to gases or mois- 

 ture condensed on the walls of the capil- 

 lary tube, and in some cases to irregulari- 

 ties in the chemical composition of the 

 glass. I found that it did not occur if 

 the tube before being used was heated 



for some time along its whole length to 

 as high a temperature as it would stand 

 without collapsing; this heating would 

 tend to cleanse the walls of the tube. 

 That differences in the quality of the gas 

 also conspire to produce these patches is 

 shown, I think, by the following phe- 

 nomenon. A capillary tube of fine bore 

 containing mercury vapor and a little 

 water vapor developed a well-marked 

 red patch; the tube was then heated for 

 some inches in the neighborhood of the 

 patch. In general, heating the tube 

 makes the discharge yellow from the 

 sodium vapor given off from the glass; in 

 this case, however, the whole of the 

 heated portion, with the exception of the 

 patch, turned yellow; the patch itself 

 withstood the heating and continued to 

 show the bright color characteristic of 

 hydrogen. 



Electrolytic Transport of one Gas 

 through another. — A tube was made of 

 the finest bore thermometer-tubing; the 

 extremities of the tube in which the 

 electrodes were fused were bent down so 

 far as to be parallel to each other, and so 

 near together that a slight motion of the 

 tube suffices to bring either of the ex- 

 tremities in front of the slit of the spec- 

 troscope. The tube was mounted on a 

 board moved by a lever; by moving this 

 the observer at the spectroscope could 

 readily bring the spectrum of either the 

 positive or negative electrode into the 

 field of view. A side tube was fused to 

 the middle of the main tube and was pro- 

 vided with two taps; in the space between 

 these taps a small quantity of any gas 

 which it was desired to introduce into 

 the main tube could be imprisoned, and 

 could, by opening the tap, be introduced 

 into the discharge tube. The experiment 

 consists in filling the main tube with a 

 gas at a low pressure, observing the 

 spectra at the two electrodes, then intro- 

 ducing by the side tube a very small 



