Deo, P G

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87INFLUENCE OF THE ELECTRODE-SURFACE ON THE JOSHI-EFFECT IN CHLORINEB y  P. G. DEO{Received for publication, April 4, igsOABSTRACT. Joshi-effect was studied in 162 mm Hg pressure chlorine contained in five ozonizers of different lengths but of identical electrode diameters in the potentialrange 1-8 kV. Both the net and relative Joshi-effect increased by increasing the ozonizerlength which is a measure of the excited electrode area. This increase shows saturation specially at low exciting potential^. The results are in accord with Jo.shi's theory that an adsorption-like electrode surface layer consisting of ions and electrons derived from the discharge space is a primary seat of this phenomenon.The spectrum of chlorine under conditions productive of a large Joshi- effecl A i  consisted (Joshi, 1943 > Deo, 1948) almost entirely of faint bands duetoCU"". The absence of any emission spectrum characteristic of atomic chlorine 'suggested that any reaction involving the latter was confined to the container surface. The surface sensitivity of At was also illustrated by the remarkable influence on its magnitude and even sign due to increase of surface to volume ratio by introducing powdered wall material in tbe dis­charge space (Shukla^ i949^ This procedure, however, alters the field strength and the nature of the discharge and irradiation. It appeared, therefore, desirable to study the surface dependance of At under comparable conditions.E X P E R I M E N T A LFive ozonizers Sj, S2, S3, Sj and Sr, (figure of lengths 19.5, 15*8, 7*9i 3.1 and 1.9 cm respectively, were prepared from the same pair of glass tubes.F ig . IIElectrode-surjace on Joshi-effect in Chlorine 469They were filled carefully with purified chlorine from a given stock at the same pressure, viz^ 162 mm Hg and excited by a transformer discharge. Each of the inner electrodes, formed with a saline solution, was connected to a common high tension line through a switch. The low tension electrodes formed with a solenoid-like winding of copper wire in well-spaced turns over the outer tubes were connected similarly to a common line which was earthed through a vaciio-junctiou feeding a mirror galvanometer. With a 180 volt, 200 watt bulb as the light source, the potential current characteristics V - i  were observed in dark and under light, when (ii all the ozoni/.cis S,,S » , S4 and 55 connected in parallel were excited ; and when each of them (ii) S2, (iii) Si, (iv^ .S3, <v; .S4, and (vi) S„ was excited separately. The results of the observations are given in Table T (figure 2).fdarli At %Ai4033II98256987^0 P. G. DeoD I S C U S S I O NIn a discharge tube of ozonizei type the entire surface is due to the electrodes. A t  a given applied potential, the nature of the field at the electrodes and in the gas phase, and especially the electrode asymmetry (Deb and Ohosh, 1946) determined by the ratio of the radius of the outer to that of the inner electrode is sensibly the same, viz. 5.5/3.3 in all the systems•Sii...... *Ss ; the area of the electrode surface given by the ozonizer length isthe only variable so far as the study of A t is concerned. It is interesting to observe ( Table I) that at a given potential, k V , applied to the ozonizer, the magnitudes of A t and % A i are in the order S ,> S 2 > S ,> S 4 > S fi. Thus, e.g. at 5.34 kV , the magnitudes of % A i in S,, S2, 5'a, S4 and 6'a are respectively 32, 25, 14, II and 6, i.e. ceteris paribus the Joshi-effect increases by increas­ing the net excited surface. In each case the magnitude of A i increases with kV , whereas, that of % A t decreases, which is in accord with the generality of the results about this phenomenon (Deo, 1944 ; Prasad 1948).Curves in figure 2 relate with the ozonizer length (which is ajneasure of the excited electrode area) the relative Joshi-effect % A i“ iooA//i dark. Hssentially similar curves (not shown) are obtained by plotting A f. Doth A i and % A i increase by increasing the electrode surface. This increase is practically linear at large kV  and slows off at smaller ones, indicative of a saturation effect. This is also brought out by considering the values of A i  and % A i wdien all the ozonizers were connected in parallel. This is equivalent to a first approxiniation to a single ozonizer of area corresponding to 19.5 + 15.8 -I-7 .9 -J-3 .1 -f 1 .9 = 48.2 cm. The observed A j and % A i at each of the series of applied kV  for the combined system, are less than those to be anticipated by an extrapolation of the A j and % A i  versus electiode length curves in figure 2, due to a saturation.It is known '.McBain, 1932) that the glass surfaces take up variable quantities of gases, and that this process may be favoured by the application of an electric field. This is illustiated by the well known clean up pheno­menon, e.g. the hardening of the X -ray lubes. Its simplest view is that the charged ions penetrate into the wall. According to Campbell (1920, 1921, 1922, 1924) neutral atoms or excited molecules produced under the discharge also take part in the process. Since rare gases also ‘ clean up/ it is suggested that the reaction may be of the physical type. W ith reactive substances, chen o-sorption is, how'ever, possible. Langm uir 11912, 1913, 1915, 1916, 1939) regards the ‘ clean up ’ of practically all except the inert gases as purely chemical in nature. Kodebush and Xlingelhoefer (1933), working with chlorine subjected to an electrodeless high frequency discharge in a glass bulb, observed a white wall deposit attributed by them to chemo- soi ption.It is important to note that in all the above type of reactions the gas pressures are much lower than those now employed. An adsorption likeElectrode-surface on Joshi-e0ect in Chlorine 471electro d e  la y e r  w ould  appear to be a deteruiinaut in the production of A t. R a o  (i 945> I94b) observed that A i in chlorine-air m ixtu res (ratio i : i)  decreased  but little , when the system  was evacuated com pletely with a topler (but n ot d ega ssed ), and the m ixture was replaced bv air alone at the original p re ssu re . T h a t the com pletion of this layer is a time reaction w as suggested  (D eo, 1945), since no .sensible ‘ ag in g  effect ' obtained in the o/.onizer after use fo r ab o u t one and a h a lf y e a rs; ilind that when freshly prepared, A f  was fo u n d  to  v a ry  appreciably w ith th e  tim e of exposure to the d ischarge. T h is  w as attrib u ted  to an interactien between the 'electrode* wall m aterial an d  a ctiv a te d  g a s undei the d ischarge. R am anaim trti (191S) observed that in  a fre s h ly  prepared chlorine-filled  jozonizer, the tim e-developm ent of A? fo llo w s equ ation  fo r * fiis t  order ’ reaction. It is suggested that the boundary la y e r  form ed  d u rin g  d isch arge is due to chem o-sorjdion involving electron tra n sferen ce  (R am anam urti, 19 1^8).A c c o rd in g  to R ebbcck  and b'urguson ( 1 9 2 4 )  the e lectiical cond uctivity of g la ss  is n ot affected sen sib ly  b y  sorbed gases. T h e y , in some cases, how ever, in flu e n ce  re m a rk a b ly  the co n d u ctiv ity  of solids for high frecjnency currents, d u e  to  a ch a n g e  in the e lectrica l cap acity  by sorption. T h is last m ight affect the accom m odation  cocfficiviit, i .r .  the degree to which reflected (O regg, 1 9 3 3 )  p a rtic le  ad justs its en ergy to the reflecting surface. It is difficult to e n v isa g e  how* the.se processes would cause a large change in the r v la i iv e  J o sh i-effcct b y  v’ariation of the electrode a iea  .Sj.. -■  .S'„. bon u ation  of an ad sorption  layer under discharge appears to be fairly  certain as the first s ta g e  in the production  of A i .  T he subsequent stages according to Joshi{1946, 1947), are the emission of e lectio n s under in adiation  Irom this layer ;and th e ir  su bsequ en t capture by chlorine atom s resulting in the slow negative ion s, c a u sin g  A / as a space ch arge effect.A  C  K  N  f> \ v  L  K  I X ' .  M  K  N  T  SG r a te fu l  th an k s of the author are d u e  to P ro f. P. N . i^hanna, D .S c ., H ead  of th e  P h y sic s  D epartm ent, L u ckn o w  U niversity for encouragem ent and to  P r o f .  vS. S . Joshi, P rin cip al, C ollege of Science, Hanaras, for valuablesu g g estio n s.D epartment o r  P h y siCvS,U n iv e r s it y  oe Du c k n o w ,R  K  h' n  R  K  N  C  E  SCampbell, and co-woikers, igzo, Pliil jVag. 40, 58.S1921, <(>('(• *2, 227i92.i, i b i d ,  43, 914”  1924, i b i d ,  48 , 5.SJD eb and Ghosh, 1946, •Sci .  and C u l t  , 12, i-..Deo, P. G ., 1948, P h i l .  Mag., 39 , 978.472 P. G. DeoDeo, p f G., 1944, Proc. Ind. Acad, Sci,, 19, 117.:Deo, P. G. 1945, Proc, Ind, Acad, Sci., 21 , 76.Glocker and Lind, 1939, Electro-chemistry of Gases and other Dielectrics, John Willy and Sons, Inc., New Yoik, pp. 426-42.Gregg, 1933, The adsorption of Gases by Solids, Methuen and Co, Dtd. I^ondon, pp. 88-89,Joshi, S,S., 1943, Prnc. Indian Sci. Cong,, pp, 51-77.Joshi, 1046. Proc. Ind, Sci. Congr., Phy^, Sec, Ahstr, 26,*9 l7i Curr, Sci. 16, ig,Langmuir, 1922, J. Am, Chcni Soc., 3i, 1310.»> 1913. ibid. 36, 105»» 1915, ibid. 87, 1157ft 1916, ibid. 88, 287999 19 J 9 . ibid, «1. 167McBain, 1932, Sorption of Gases and Vapouis by Solids, George Routlcdge and Sons Ltd, London (1932).Prasad, B.N., 2948, Curr. Sci,, 17, 235.Ramanamui ti, y. Ind. Chem, Soc., 23, 255.Rao, 1945, Proc. Ind. Sci. Congr., Chem. Sec. Ahsi, 23;,, 1948, Proc. Ind, Acad. Sci., A27, 72.Rebbeck and Ferguson, 1924, J. Am. Chem Soc., 46 , 2000.Rodebush and Klingelhoefer, 1933, J. Am. Chem. Soc., 66, 030.Shukla, 1949, ] .  Phy. & Coll. Chem , 63, 1239.

Influence of the Electrode-Surface on the Joshi-Effect in Chlorine

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Influence of the Electrode-Surface on the Joshi-Effect in Chlorine

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