OXZDISING PROPERTIES OF SULPHUR DIOXIDE. PART I. 1093 CXXIV.-The Oxidising Properties of Sulphur Dioxide. Part I. Iron Chlorides. By WILLIAM WARDLAW and FRANCIS HERBERT CLEWS. As this paper has tol deal with the reactions of sulphur dioxide and metallio chlorideti it may be well t a summarise our prewnt know-leldge relative to this subjeat. The olxidation of stannous chloride by sulphur dioxide in the presence of concentra,ted hydrochloria acid has been shown (Smythe and Wardlaw Prqo. Durham Phil. Soc. 1914 5 187) ta prowed quantitatively t o campletion according to the quatian 3SnC12 + SO + 6HC1= 3SnC1 + 2H20 + H2S. Sulphurous acid ie reduced by titmous chloride t a hypoaulphurous acid (Kneoht Ber. 1903 36 166) and its further reduction to sulphur was noltiwd by the same inve&gator.Smythe and Ward-law (Zoc. &t.) further proved that when sulphur dioxide is passed into a warm strongly aoid solution of titanous chloride hydrogen sulphide is freely evolved. Sulphur is formed by secondary relau-t4ion between the hydrogen sulphida and the sulphur dioxide and if the emaping hydrogen sulphide is led into an excess of sulphur dioxide in colnaentrateld hydrochloria acid the reaction whiuh goleis to compleltioa may be quantitatively summasised as follows : 350 + 12TiC1 + 12HC1= 12TiC1 + 6H20 + 3s. The &ma authors (201~. cit.) have shown that sulphur dioxide olxidises meruurous chloride in the praence olf conmntrahd hydroahloria aoid according to the equation SO + 4HC1+ 2Hg,Cl,= 4HgC1 + 2H20 + S. I n the same paper it was mentioned that in concentrafted hydra-chlorio acid ferrous chloride is oxidised by sulphur dioxide ta ferrio chloride with tlhe farmatlion off sulphur.No sulphuria aoid was debated in thei solution. This mactioln diffelred frm those alrelady quoted in that olxidatlion under the mmt favourable coaditions prolaeedeid olnly to a limited exteellltc the average yield od ferria iron in all the experiments being 7 per cent. of the total iron preselnt, the extremes being 4 and 11.6 per cent. I n these experiments, rigid aotntrol was not exercised olver the colnditioas of temperature, mnaentration eta. and it seemed desirable therefore that a systematic investigation of this reimtion should be carried out*. VOL. axm. T LO94 WARDLAW AND CLEWS THE OXIDISING EXPERIMENTAL.The general methold of procedure was as follolws. Pure ele,ct,ro+ lytdo iron was diwolveld in pure oonaentrafed hydrochloric acid contained in a flask madel entirely of glass and such that t,he react-ing gasea coiuld be passeld t,hrough the solution cont'aineld in it. This was connelcted with wash-b,ottlet+ contlaining wa,tes aad sodium hydrolxidel solution respeotively. Thew serveld t,o absorb the effluent sulphur dioxide! and hydrogen chloride and to1 exclude air, and so prevent atmospheric oxidation. The1 ternpelrature of the, flask was; controlled by immersion in a.n oiil-ba,th. A stream of aarbon dioxide was clontJnuoudy passed through the a,pparatus during t'hel sollutioln olf t'he rnet(a1. Whein the iron 1ia.d completely dissollved the flask was mnnecltad with a sulphur-diolxide syphon and t'hhe gas passeld for a.sta,ted pelriold. It was' nolticed that after the sulphur dioxide ha,d paissed folr at few minutes the so(lut,ion changeid to olivegree'n thea t'a relddish-brolwn a'nd beloamel dis-tinotly opa.lescent ofwing tlol the separation of sulphur. After t8hel rea,otioln ha.d proceledeld f olr the relquireld t'imel tlhe sulphur dioxide wa5 displaced by ca'rb'oln diolxidel the sollution ao1ole;d in a strelam 04 the sa;llle gas a.nd the iron titrabd aSt.er suit,a#b#le dilut8iolri witlh a,ir-free water with sta.nda,rd poltaasium dichroma'te accolrding ta Zimmernmnn a,nd Reinha,rdt's methoid. The sulphur was de,kmined by fi1t'ra)tion aad direlot weiighing . Quantitative Aspect of the Reactioln.Them are two possible reiaations involved colrresponding (a) with direlct reduotion of the sulphur dioxide to sulphur and ( b ) with initliad relduction of the sulphur dioxide to hydrogeln sulphide which react8 with ~ O ~ B S od sulphur dioxidel forming sulphur. Both retactions are represenhid finally by the equation SOz + 4HC1+ 4FeC1 = 4FeC1 + 2H,O + S, so thah it is impolssiblel t o l deicidel quantitativefly betlween the two. Morwvelr ming to the1 fact that the limit of reaction has been shown to be sooln reached the amurate estimatioln of the sma,ll quantity of sulphur is very diffioult. The following are examplee olf the results obt'ained by Smythe and Wardlaw (Zoc. cit.). TABLE I. Sulphur. Ferric iron & Experi - Concentration of produced. Found.Calc. ment. f crrous solution. Gram. Gram. Gram. 1 5.893 grams Fe per 100 C.C. 0.683 0.062 0.098 2 4.468 ,) )) 200 C . C . 0.392 0-040 0.056 5.450 y y y 200 C.C. 0-340 0.035 0.048 PROPERTIES OF SULPHUR DIOXIDE. FAltT I. 1096; The wnalusion to be drawn is that tlhe equa,tion melntioaeld above repreeents the reaction. From general considerations one is also led ta infer that i t undoubtedly fdlolws the course (a). Although hydrogen sulphide has never bem directly d e h t e d in the reaction, from the fact that sulphur is formeld in the neck of the flask and in the outlet tubes i t is pmsible that the reaction follows the course ( b ) to a vary limited extent. Znfluence of Cmcmtratiofi of Toltd Iron. A range of coincantrations of iron was invwtigated by dissolving varying quantities of iron (1-10 graxns) in 250 C.C.of concentrated hydrolohloric aoid. Sulphur dioxide was passed through the1 solu-tion for four hours a t 1 1 5 O a,nd the amount olf ferric salt subsequently determined by titration. TABLE 11. Experiment. 4. 5. 6 . 7. 8. Grams of iron dissolved in 250 C.C. of mid ........................ 1 3 5 7 10 Ferric iron per cent. ............ 5.3 4.2 3.4 3-3 3.6 These rault,s tend to show that the limit- of ocxidation is not influenced by the initial conaelntratioln of tahe iroa. The conmn-trafion of the hydrochlorio auid is not exactly constant in these elxperiments awing t o tghe varying loma o€ hydrogen chloride during the solutioln olf the diffsrelnt qua,ntitiss of metal and this undolub,tedly influenoes the degree of oxidation.TABLE 111. InfEu,ence of Temperature. Comentratiofi.-Two grams of iron in 100 O.C. of concentrated Dumtiom of Experiments.-Twa and a-half hours. hydrolchlorio acid. Experiment ............ 9. 10. 11. 12. 13. 14. 15. Temperature ......... 61" 70 79 93 115 125 gently boiling. Ferricironpercent .... 1.6 3.0 3.5 5.2 3.8 3.0 2.8 The existence of a.n optimum temperature (approlximatdy 950) is the rwdt of two or more oppwing fad.ors. The reaation-vetlocity will be favoured by an increaser in temperature whilst the higher temperature will lead to a mom rapid lms oif hydrochlorio a,cid, T T 1096 WARDLAW AND CLEWf3 THE OXIDISING espelcially in the early stages of the reaction. It is also highly progbable tha,t the sollubility of the sulphur dioxide decreases with rise in temperature.Zmflueirzce of the Comcentratiom of Hydrochlom'c Acid. The tlhreie following elxperiments are moldificatioas of those described in ta,ble I11 with a view t,o change the conmatration of hydrochloria aoid. Values from table I11 are a4dded for comp arism . TABLE IV. Coincmtmtiow.-Two grams olf iron dissolved in 100 0.0. of Dumtioln of Experimemt .-Two and a-half hours. concantr ahd' hydrolohloria acid. EX.-peri-ment. Description. From Table 111. x 100. Ferric iron. Per cent. Ferric iron Per&- -__ fure. Total iron 16 Sulphur dioxide passed through concentrated hydrochloric acid a t 95' before being led int.0 the ferrous chloride solution ......... 9Eie . 7.8 5.2 Mixture of hydrogen chloride and sulphur dioxide (60 per cent.of HC1 by weight)* passed into ferrous chloride solution ......... 115 4.7 3.8 18 Carbon dioxide passed through ferrous chloride solution at 115' for 30 minutes and then sulphur 17 dioxide for 2+ hours ............... 115 1.3 3.8 * In all cases the composition of gaseous mixtures of sulphur dioxide and hydrogen chloride will be expressed by the percentage of each constituent by weight. The increased yields in experiments 16 and 17 and diminished yield in axperimelnt 18 in which exaess of hydmohlotrio a'oid is removed from the sollution show thab the oixidising elffeict olf sulphur dioxide is only appreciable ast co,ncentra-tJons exceeding that of the mixtturel olf colnst'a,nt boiliklg polnt. Accoirdingly in the1 netxt experiments (table V) iroln was dis-solveld in hydrochlorio acid diluteld to1 the aonw'nt'ratioa of the, mixt8ure of oonsta.nt boiling point and a mixture olf hydrogein dhloside and sulphur dioxide in different proportions passeld into t'he ferrolus ohlotride solution.The ratio of sulphur diolxide to hydrogen chlocride wa.s olbserved by divelrtling a s,ma,ll prolportion od the gaMee by me1a.w od a T-piem, while tih.e experimentl wa.s in progress. The acid gasels were absolrbd in 50 a.a. od N-soldium hydrolxider thel chloride being sub PROPEIMIIBIS OF SULPHUR DIOXIDB. PART I. 1097 wquently titratad witch etmda,rd silvelr nitrate and ammonium thioIoyana,tel and the sulphib with standa*rd iodine and sodium $hiosulphak. TULE V. Gmcentratiom.-Two grams olf iron dissolved in 100 C.C.of Duration of Experimemt .-Four hours. hydrcwhlolrio acid (22 per cent. HCl). T e ~ ~ ~ ~ ~ ~ t ~ e . - 1 1 5 0 . Percentage composition of mixed gases. I c- I Ferric iron x 100. Experiment. so2. HCl. Total iron 19 81.7 18.3 20 56.7 43.3 21 22.5 77.5 23 10.1 89.9 22 15.8 84.2 2-3 2.2 4.2 8-6 3.9 The results shosw that for the colnditibns desmibsd in the above, experiments hhere is a cmnpamtlivelly na'rrow range of composition between 10 and 20 per cent. of sulphur dioxide which is most favourable for the olxidation of ferrous chloride a maximum beling maohed in the neighbourhood of 16 pelr cent. of sulphur dioxide. Limiting Concentration of Hydrochlovic Acid folr Oxidation uf Ferrous Chlwide b y Sulphur Dioxide.Since in dilute1 hydrochloria a8cid solutio8n sulphur dioxide com-pletdy reduaes ferric chloride to ferrous chloride there will be TA,BLE VI. Temperatwe .-95O. Duration of Experiment .-Four hours. SoZutiom.-Five grams of iron dissolveid in aoid speoified in columns 2 and 3. Concentrated Free HCl in hydrochlorio 1000 C.C. of Expcri- acid. Water. solution. ment. C.C. C.C. Gram. Remarks. 40 160 + 90 210.5 Little oxidation; about 0.6 41 140 + 110 179.3 Very little oxidation; not 42 130 + 120 165.8 Minute oxidation ae shown 43 126 + 126 165.1 No oxidation as shown by per cent. measured. by sulphur depmit. sulphur deposit 1098 WARDLAW AND CLEWS THE OXIDISTNG some' oonceatration of acid below whioh it is impossible to1 observe the midation of ferrous chlolride by sulphur dioxide.Iron was dissolved in acids olf different concentrations and bhe action oif sulphur dioxide f o r four hours a t 950 was observed. For the1 analysis a portion of the solution was withdrawn, weighed and afteir removal of the sulphur dioxide diluted t o a convenielnt volume. The iron and total chbride were1 deltermined, and from thel differemel the (( free1 " hydrochloric acid was caluu-lateld. The1 specific gravity of the1 remainder of the solution was determined in order to stlate the concentration in grams per litre (see1 table VI). It is concluded that oxidation by sulphur dioxide1 doe@ nolt occur in ferrous ohloride solutioas contlaining less than 165 grams pelr litre of (( free " hydrogen chloride.Limit of Odatioln of Fcrrows Chloride b?y S d p h w Dioride in Hydrolchlovic A cid Solutiorz. (a) Experiments at A tmospheric Pmssure.-With the1 purpose of determining the limitl ojf oxidation use1 was madel of a rather larger flask fitteld with a water-cooleld exit t u b and containing an amoluntl of solution sufficieat to1 profvide two1 samples for analysis. Five grams of iron dissolved in 250 C.C. of cioncreatrated hydro-chloric acid (33 per mnt.) were treateld with hydrogen chloride and sulphur dioxide at 1 1 5 O as describe'd in the following cnpeaimenh TABLE VII. Time of taking' sample from Expri-ment. 24 25 26 27 Description. Hydrogen chloride and sulphur dioxide (80 and 20 per cent,.) passed continuously into ferrous chloride solution.Rydrogen chloride and sulphur dioxide (50 per cent.) passed into ferrous chloride sohition. Sulphur dioxide alone passed for half an hour then hydrogen chloride and sulphur dioxide (50 per cent.) cont.inuoiisly. Sulphur dioxide alone passed for hnlf an hour then hydrogen chloride and sulphur dioxide (80 and 20 per cent. PROPERTIES OF SULPHUR DIOXIDE. PART I. 1099 TABLE VII (continued). Time of taking sample from commence-Experi- ment of Ferric iron msnt. Description. experiment. Total iron 'O0' 25 *The ferrous chloride solution was alternately cooled to 30' (1 hour) 3 hours 6.5 and then quickly raised to 115' (heated for 2 hours) hydrogen chloride and sulphur dioxide (50 6 , 7.0 per cent. of each) passed contin. uously ). 29 Experiment 28 repeated but cooled for 1 hour and heated to 115' for 6 , 8.8 1 hour.* This procedure enabled the solution to absorb a large amount of the gases at the lower temperrtturos. On rapidly raising the temperature to 115' the solubility values would not be attained immediately and during this interval tho temporarily increased concentration of hydrochloric acid and sulphur dioxide would be available for reaction with the ferrous salt. An oxidation od 8.8 pelr c a t . (in experimelnt 29) is the1 highest obtained by the action of sulphur dioxide on ferrous chloride opelrating undelr al pressure1 slightly in eixoelss olf the atmosphelrio. ' (b) Experiments with SeaEed Tubes.-A rather higher degree od oxidation u7as olbtaineld by the1 use of a seded tubs.Expt. 30.-Half a) gram of iron was dissolved in 10 a.0. of uon-celntrated hydrochloric aaid in a Carius tube in a current of carbon dioxide. The tube was i m e r w d in ice the solution saturated with sulphur dimide and the tube waled. It was then helated at looo f o r six hours and allowed to ooloil ovelrnight. Titration showed that olxidatioa had occurreld to the extent of 9.5 pelr cent. a value only slightly in exce8s of those obtained under normal pressures. L h t i t of Reduction of Ferric Ch1ori.de by Sulphur Dioxide in Concentrated HydTschlork Acid Solution. (a) Expen%nents wtder A tmospheric Pressure.-It is well known tchat exmss of hydrolchlorio acid prevent6 the comple!b reduation of feirrio ohloride by sulphur dioxide (Tresdwell and Hall '' Quanti-tative Analysis," 5th ed.p. 607 footnote). It was not known, hoiwewr t o what concentration of hydrochlocrio acid this referred or the extentl to which feirria chloride ww reduced. Since1 the reiduotioln od ferria chloride1 in ocmoentratd hydro-chloric aoid was found to proceed slowly mixtures s f felrrous and ferric ohlorid- were prepared and their compositions determined 1100 WARDLAW AND CLHW8 THH OXIDlST" bolth before and after passing sulphur dioxide and hydrogeln chloride (approlximatetly 50 per aent. od each gas) for a definib timei. By this means the value t'ol which the reduction would eventually att'airia was eatimacted. TABLE VIII. Cmcentmtiow.-Five p m s of iron in 250 U.C. of hydrochlolrio Ttmperature.-115°. Gas.-SO,+ HC1 (50 per cent.mixture). ataid (33 per cent.). Experi-ment. 31 32 33 34 36 36 37 Duration of experiment. Hours. 4.0 4.0 6.3 4.0 6.0 2.5 6.6 x 100. Ferric iron Total iron - value. 100.0 72.2 63.8 42.1 20.7 18.3 10.8 7z.2 value. 78.2 68-8 48.6 39.3 18.3 18.3 10.7 Reduction gradient (average reduction per hour). Remarks. 6.4 Sulphate formed. 0.98 ? Y 0.84 ? Y 0.70 ?? 0.40 YS I No sulphate. - -No sulphur wa8s folrmed in any of the above expelrimsnta, Apparently iroln aollutioas containing more than 18.3 per cent. 8f ferric iron are slowly relduwd by sulphur dioxide in the presenm of cancantrateid hydroahloria acid. There seems also to be a ranger of from 10 to 18-3 per cent. of felrria iron in which there is no evidetnm of reduction or oxidation by the sulphur dioxide during the time 04 the experiments.Evidently this reipremnte a zone in which the rate of rea;ctim otf the sulphur dioxide is very slolw. The solutioln in experiment 37 was analysd and it was shown tlo aontain in 1 libre 239 grams of '( frw " hydrmhloric a'uid and 0.314 gram ot sulphur dioxide. (b) Experiments in Sealed Tzcbes.-Five grams of ferrio chloride were dissollveld in 10 0.u. of hydrochloric acid (33 per cent.) and the solution was saturated with sulphur dioxide at 0". The tubs was selaled and hea,ted to l l O o for folur hours. Analysis showed a reduction od 20.6 per cent. and sulphuria acid w&s detected in the solution. A similar experimeint after twenty-five hours at l l O o gave only 22.3 pelr cent.of reduction. ApparenUy the high con-mntration olf hydrolchlmio aoid whioh exists in a c l d vessel inhibib the reduction by sulphur dioxide just as a high concen-tration of acid appears also to favour the oxidation of ferrous ahloride PROPERTIES OF SULPHUR DIOXIDE. PART I. 1101 Reductim of Ferric Ch1om.de b y Sdphur. Stokm (Bull. U.S. Geob. Survey Nor. 186 1901) has e x m i n d the &ion of pyrites and mwoasite on a hoh dilute solution of ferrio chloride and observed reduction la a considerable extent (65 per oent. of the sulphur) the sulphur being olxidid ta sulphurio acid. The premnt authors find t'hah the action of sulphur in conmntlrated hydrachlmia acid on ferrio chloride is slight. A solution of 5 grams ~f ferria chloride in 60 0.0.of conwntrafxd hydrwhlcria aaid was boiled in an atmmphera of aarbon dioxide for olne and a8-half hours. The reductioln oorrapondd with 0.66 per c a t . t a b sulpbur being oxidised to sulphurio add. A solution od 3 grams of feirrio ahloride in 50 0.0. of concentrated hydroshloilrio alcid to whioh 50 0.a. of colloidad sulphur solutdon were added on boliling for one and a-ha,lf hours raulted in 1.7 pelr cent. od retduc-tion. Sulphuric acid wars produced. Experiments on the linm of tho(% sholwn in ta,ble VIII in which a prolportioin of finelly divided sulphur was added showed that it exerted very little reducing aation in comparison with the sulphur dioxide. SUrn;mCM.y. (1) The axidamtion of ferrous ohloride by sulphur dioxide o m be reprwelnbd quantitahively by the eqpation 4FeCl + SO + 4HC1= 4FeCI3 + 2H,O + S.(2) The degree od oxidation is independent of the initial concmntration of total iron. (3) The most favoura,ble temperature for the oxidation by sulphur dioxide of a solution of ferrous chloride in 33 per oent. hydroohlaria acid is 95O. (4) Oxidatlion by sulphur dioxide at 95O doles not occur in solu-tions of ferrous chloride containing less than 165 grams per litre of " free " hydrogen ohloride. (5) A solution of ferrous chloride in hydrdlolria aaid of oonstant boiling point (22 per cent.) a t 115O gave it maximum. olxidation of 8-6 per u e n t . (felrric iroln) when treated with a mixture of sulphur dioxide and hydrogeln chloride containing 16 per cent. of sulphur dioxide. Mixtures containing 10 t a 20 per cent.of sulphur dioxide are mast favourable for oxidation under the above conditions. (6) The highest percentcage of ferric iron obtained in any of tlhe flask expm5mdis reoordeld in this paper was 8.8. This result was produced by trelatment of a ferrous chloride solution in 33 per cent. T T 1102 WARDLAW AND CLEWS THE OXIDISINO hydrwhloria mid a t 115O with a 50 per cent. mixture of sulphur dioxide and hydrogen ahloride under special colnditions. (7) Sealed-tube experiments gave a maximum oxidation of 9.5 per cent. of ferric iron. (8) Iron sollutioiis containing 10 to 18.3 pelr cent. of ferric iron in 33 per writ. hydrochloric acid a t 115O sholwed no evideince of oxidation o r reduction when a 50 per cent. mixture of sulphur dioxide and hydrogen chlolridel wasI passed into them for varying periods.(9) Under the same experimeatd aonditions a's in (8) iroa solutions contlaining more than 1S.3 per oelnt. of ferric iroln weire slowly r e d u d . (10) Ferric chloride in aonaentrated hydroahloric aoid was reduced to a smadl extank by sulphur. Th e o ~ e t i c d . The oxidation of a felrrous chloride solution by slulphur dioxide has been shown to be quaatitative~ly reprewnted by the equation 4BeC1 + SO + 4HC1= 4FelC13 + 2H,O + S . . . (1) Moreoveir since sulphur is able t o relduce ferric chloride to some extent it seems justifiable to assume that the above equation is reive~rsible. 4FeC1 + SO + 4HC1 4FelCl,+ S + 2H,O . . . (2) This fact is generally obsaured however by the motre gelneral q u a ti on 2FeC13 + SO + 2H,O = 2FeC1 + 2HC1+ R,SO .. . (3) Since no sulphuric acid is detelcted when a pure felrrous chloride sollutdon is oxidised by sulphur diolxidel in the1 preselnce oS minoen-trated hydrochlorio acid it oan be1 assumed that under these con-ditions the reaction Lhat oloours is sollely reprelsentled by equation (2). Molrelover seeing that sulphurio acid is only detteoted when sulphur dioxide in the prsence of concentrat.ed hydrochlorio acid reads with iron sollutdoas containing motre than 18.3 per cent. of felrria iroln it appears that reaotioa (3) is only olperative i n such solutiolns. The idela tha't a reversible reactiota takes place when pure ferrous chlolride soflutioln is oxidised by sulphur dioxide recelivesl added sup-port fmm the faat that only a limited yield od ferria salt is possible,, and thak the reactlioln is not greatly influelneed by the initial con-centratioln of totall iroln.Applying the lalw of mass action to1 equation (Z) it appears that for a given concentration of sulphur dioxide and hydrogen chloride the equilibrium position would b PROPERTIES OF SULPHUR DIOXIDE. PART I. 1103 determined solely by tlhe raltio of ferrous to ferria iron assluming that the active masw of the sulphur alnd water are aonstant. The importance of a high colncentratioln of hydrogen chloride ta bring about the oxida,tion also follows logically from the idea of a ballaaaeid relaction. The dependence of sulphur dioxide as an oxidising agent on a high concentration olf hydrochloric aoid has led to tha suggelstion that hydroohloria acid and sulphur dioxide interact f oming thionyl chloride la a small extentl (Smythe and Wasdlaw Zoc.c i t . ) . This idea receives support from the following reaotions with the marcaptans : SOC1 + 4R*SH = %S2 + R2S3 + H20 + 2HC1 (Holmberg AnmaZen 1908 359 Sl), (Smythe and Forster T. 1910 97 1195). SO,[ + HCl] + 4R*SH=&S2 + RZS + 2H,O[ + HCl] 011 this assumption the reaction SOC1 + H20 SO + 2HC1 must be reversible. Although this has not been proved direotly, them is some indirest evidence in that when thionyl chloride reacts with memaptans at law temperatures (Oo to -70°) hydrogem chloride and sulphur dioxide are evolved and water is fmnd among the residual prolduats (Taskelr and Jones T. 1909 96, 1904 1910). I n addition the reactions of the sulphoxidw and the halaid adds are to some extent analogous. (Zincke and Frohneberg Ber. 1910 43 837), (CH,Ph),SO + 2HBr (CH,Ph),SBr,+ H,O ( F r o m and Raiziss A d e n 1910 374 90; Fromrn ibid., 1913 396 75). From this idea the question arises as tIo whehher the oxidising properties af sulphur dioxide ara only opemtive in the preselnoe of concentraked hydrochlorio acid. Experiments have been in progrws to determine this point and the results will be cmmunioahed in a further paper. CH,-SO*C,H,*CH + 2HBr CH,*SBr,*C,H4*CH3 + H20 THE UNIVERSITY, BIRMINGHAM. [Received August 12th 1920.1 T T*