SErTEMBKK 5, 1 895] 



NATURE 



451 



writers of history and Ijiograjihy and literature dividing into 

 various classes, and finally there is the tendency of men of 

 letters to unite into corporate bodies — an integration which has 

 only become possible in recent years. In the same magazine, 

 under the title " Heredity Once More," Dr. Weismann replies 

 at length to an article contributed by Mr. Spencer to the magazine 

 last October. 



Mrs. Percy Krankland writes popularly on " .Sunshine and 

 1-ife," in I.o>ii;man's Magazine, which also contains an account, 

 i>y Mrs. A. Lang, of the Rev. John Mulso and his unpublished 

 letters to Gilbert White, of Selborne, whose aller ego he was. 

 Miss A. Lorrain Smith describes "Ants as Mushroom 

 I Growers "in an illustrated article in Good Words: her paper 

 deals with the leaf-cutting and fungus-growing ants of Nicaragua. 

 The Siinilay Magazine has "a second paper by " Eha," on 

 Indian jungle life. Knoii'ledge contains an account of I*rof. 

 I'etrie's conclusions with regard to a "Newly-found Race in 

 Kgypt " ; and papers on " Wind-Fertilised Flowers," by the 

 Rev. A. S. Wilson; "Satellite Evolution," by Miss A. M. 

 Gierke ; " Photographs of Elliptical and Spiral Nebula- " (with 

 1 plate), by Dr. J. Roberts ; and " Blind Cave-.Animals," by 

 Mr. r-t. Eyflekker. Chaiiihers's foiirnal Cfmtains short pojtular 

 articles on " Cordite and its Manufacture," and " The Prospects 

 uf our Descendants in regard to Stature," and a gossij) on the 

 ( ;reat Auk. 



We have received, in addition to the periodicals named in the 

 foregoing, Scribner s Magazine, and the Humanitarian. 



ON THE ELECTROLYSIS OF GASES.' 



T N the experiments described in this paper I have used the 

 spectroscope to detect the decomposition of gases by the 

 electric discharge and the movement of the ions in opposite 

 directions along the discharge-tube. 



The method consists in sending the electric discharge through 

 .1 tube so arranged that the spectra close to the positive and 

 negative electrodes can easily be compared, the presence or ab- 

 sence of certain ions at these electrodes can thus be ascertained. 

 This method is capable of much w ider application than the one 

 1 previously used in my experiments on the " Electrolysis of 

 Steam" {/'roc. Koy. Sot., vol. Hi. p. 90), the use of which is 

 attended with very great difficulty for any substance other than 

 ileam. The earlier method has, however, the advantage of 

 lieing a quantitative method — the present one is only qualitative. 



In my former experiment with steam, when I worked at 

 atmosjiheric pressure and varied the length of the spark, I 

 l'>und that when the spark-length exceeded a certain length, d.^, 

 ihere was an excess of hydrogen at the negative electrode and of 

 nxygen at the positive, equal in amount to the quantities of 

 hydrogen and oxygen liberated from a water voltametei placed 

 in .series with the steam-tube. When the sparks were shorter 

 than a certain length, r/j, the hydrogen appeared at \\\c posilive, 

 the oxygen at the negati-;- electrode, but the quantity of these 

 gases was again etjual to the quantities liberated in a water 

 \'>ltameler placed in .series with the .steam-tube. 



When the spark-length was between rf, and d.^ the eftects were 

 irregular, and there seemed to be no connection between the 

 .unounts of gases liberated in the steam-tubes and those liberated 

 in the voltameter. 



In the following experiments in which the sparks were of 

 I onslant length and the pressure was altered, corresponding 

 irtects were observed. Within certain limits of pres.sure definite 

 and perfectly regular evidence of the .separation of the ions of 

 he gas sparked through was obtained; and the electrode at 

 n hich a given ion appeared could be reversed by altering the 

 pressure ; there was, however, a range of ])ressures in which the 

 >eparation of the ions was either not well marked or was 

 irregular in character. 



I .shall begin by describing a very sinqile method of show^ing 

 ilie separation of the ions produced by the discharge of electricity 

 ilirough a compound gas such as hydrochloric acid gas, which is 

 applicable when the discharges through the constituent gases of 

 ihe compound are o'" distinct and dififerent colours; this is 

 eminently the case with the hydrochloric acid gas, as the dis- 

 charge through hydrogen in a capillary tube is red, through 

 chlorine green. 



Take a capillary tube of very fine bore, the finer the better 



' Paper read at llic Royal Society, by J. J. Thomson, M .\., K.R.S., 

 ' .ivemlisli Professor of Kxperiiuental Pli\-sics. Caniltritlije. 



NO. 1349, VOL. 52] 



(the tube I used was thermometer tubing of the finest bore I 

 could jirocure), and insert platinum wires for electrodes in two 

 small bulbs blown on the ends of the tube ; then fill the tube 

 with HCl gas, allowing it to run through the lube for a con- 

 siderable lime .so as to get rid of any extraneous gas, and 

 exhaust the tube so that the gas in it is at a very low pressure. 

 Then when the discharge from a large induction coil passes 

 through the tube, the following phenomena are observed. When 

 first the discharge passes through the tube the colour is uniform 

 throughout and of a greenish-grey ; after the discharge has been 

 passing for a little time the end of the tube next the cathode 

 gets distinctly red, whilst that next the anode gets green ; this 

 difference in the colour at the ends of the tube goes on in- 

 creasing 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 colour attains a maximum 

 value, and if the discharge is allowed to run for several hours 

 the contrast between the two ends disappears to a very great 

 extent ; the discharge throughout the whole of the tube being 

 pinkish and apparently passing mainly through hydrogen. This 

 is doubtless due to the diffusion through the tube of the hydrogen 

 which in the earlier stages of the discharge had accumulated 

 about the cathode ; one advantage of using very narrow tubes is 

 that with them this diffusion is slow. When the lube is in this 

 condition the colour 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 discharge from 

 one constituent to another of a mixture of gases is not in- 

 frequently 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 palchy 

 appearance, some portions of the tube being a much brighter 

 red than the others, while other portions were green. In .some 

 tubes this occurred to such an extent that the discharge showed 

 an irregularly striated appearance. This eflcct is due, I believe, 

 to gases or moisture condensed on the walls of the capillary tube, 

 and in some cases to irregularities 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 phenomenon. A capillary- 

 tube of fine bove containing mercury vapour and a little water 

 vapour developed a well-marked red patch : the tube was then 

 heated for some inches in the neighbourhood of the patch. In 

 general heating the tube makes the discharge yellow from the 

 sodium vajiour given oft" from the glass ; in this case, however, 

 the whole of the heated portion, with the exception of the patch, 

 turned yellow : the patch itself svithstood the heating and 

 continued to show the bright colour characteristic of hydrogen. 



Eiedrolytit Transport 0/ one Gas titrough another. --.\ tulie of 

 the sha])e shown in Fig. I was made of the finest bore ther- 

 mometer-tubing ; the extremities, 1: and n, of the tube in which 



:5=S= 



Fic. I. 



the electrodes were fused were bent down so as to be parallel to 

 each other, and so near together that a slight motion of the lube 

 suffices to bring either of the extremities in front of the slit of 

 the spectroscojie. The tube was miiimted on a board moved by 

 a lever ; by moving this the observer at the spcctrosco|)e could 

 readily bring the spectrum of either the positive or negative 

 electrode into the field of view. A side tube, .x B, was fused to 

 the middle of the main tube and was provided with two taps : in 

 the space between these tajis a small quantity of any gas which 

 it was desired to introduce into the main tube could be im- 

 prisoned, and could, by opening the tap A, be introduced into 

 the discharge tube. The experiment consists in filling the main 

 tube with a gas at a low pressure, ubseiving i)ii- Nii,-,-rra a: t!ie 



