THE UNIVERSITY OF ILLINOIS LIBRARY I3\S WIS.

Transcription

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2 THE UNIVERSITY OF ILLINOIS I3\S WIS. LIBRARY

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5 A SYSTEMATIC SEPARATION OF THE ACIDS OF GROUP 1 BY HERBERT AUGUST WINKELMANN B. S. Nrthwestern Cllege, 1914 THESIS Submitted in Partial Fulfillment f the Requirements fr the Degree f MASTER OF SCIENCE IN CHEMISTRY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS 1915

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7 UNIVERSITY OF ILLINOIS THE GRADUATE SCHOOL June 1, HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY SUPERVISION BY HERBERT AUGUST WINKELMANN ENTITLED A SYSTEMATIC SEPARATION OF THE ACIDS OF GROUP I. BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF WASTER OF SCIENCE, in Checietry In Charge f Majr Wrk Head f Department Recmmendatin cncurred in: Cmmittee n Final Examinatin

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9 The writer desires t take this pprtunity f thanking Dr H. C. P. Weber fr the assistar.ce and helpful suggestins extend ed him during the investigatin f this prblem; and fr his val uable aid in the crrectin and arrangement f the material fr publicatin.

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11 TABLE OF CONTENTS. I. Intrductin 1 II. Separatin f Ferrcyanides and Ferricyanides 4 III. Separatin f the Remaining Anins 5 A. Study f Effect f Ammnium Hydrxide n Silver Salts 5 B. Study f Lead Salts f Grup I 6 C. Study f Mercurua Salts f Grup I 7 D. Study f Effect f Reducing Agents n Silver Salts 8 page Silver Idide Nt Reduced by Sdium Frmate 10 E. Study f Cuprus Salts f Grup I 11 IV. Prcedure 14 Prcedure I. Precipitatin f Ferricyanides and Ferrcyanides 14 Cnfirmatry test fr Ferrcyanide 15 Cnfirmatry Test fr Ferricyanide 16 Sensitiveness f the Ferriand Ferrcyanide Tests 17 Prcedure II. Silver Precipitatin, a Sepratin frm Remaining Grups 18 Prcedure III. Frmate Reductin 18 Prcedure IV. Treatment f Frmate Residue fr Idide 19 (a) Thallium Test fr Idide 19 (b) Oxidatin f Idine by Ferricyanide 19

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13 page (c) Treatment f Frmate Residue fr Sulfide 20 Prcedure V. Precipitatin f Cuprus cyanide and Thicyanate 30 Prcedure VI. Treatment f the Cuprus Precipitate t identify the Anins 21 Prcedure VII. Treatment f Cuprus Slutin fr Chlride and Brmide 21 Cnfirmatry Tests fr Chlride and Brmide 22 Nn-interfering Actin f Other Anins in the Chlride Test 33 Limits f Sensibility f Each Anin in Absence f the Other Anins 24 Eimits f Sensibility f Each Anin in Presence f the Other Anins - 24 Outline f the Prpsed Scheme - 27 V, Experimental 30 Cnstitutins f Stck Slutins 31 Results f First Analysis, Shwing- Pr Manipulatin 32 Results f Average Analyses, when Scheme was was Carefully Carried Out 33 VI. Summary 34

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15 . LIST OF TABLES page Behavir f Lead Acetate with VariBs Salts 7 " MSrcurus Nitrate 7» " n» n Silver Chlride 8 " Brmide 8 Actin f Reducing Agents n Silver Salts S (a) (b) (c) Frmaldehyde Frmic Acid Sdium Frmate Behavir cff Cuprus Salts in Presence f SOg 11 Sensitiveness f Test with Zinc Nitrate fr Ferricyanides and Ferrcyanides 17» 11 " " KBr, " " " " " 25 «" KI, " " " 25»'»' KCN, b 25 " IC 3 Fe(CN)»'_ 6 " " * " " 26 " K 4 Fe(CN) " «6 26 Zinc Ferricyanide Reactin. Reliability in Presence f Other Substances 17 Zinc Ferrcyanide Reactin. Reliability in Presence f ther Substances. 18 Behavir f Thallium Nitrate in Presence f Idide 19 Sensibility f Each Anin in Absence f Others, Carried thrugh the Scheme 24 Behavir f KC1, presence f 200 mg. f Other Anins KCNS, " " " " " " 26 Outline f the Scheme Cnstitutins f Stck Slutins 31 Result f First Analysis 32 Results f Final Analyses 33

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17 A SYSTEMATIC f SEPARATION the ACIDS OF GROUP I I. INTRODUCTION Very little wrk has been dne upn a systematic separatin f the acids. The custmary methds fr the recgnitin f the varius acids depend mainly upn the varius grup reactins, fllwed by specific tests fr ne r the ther anin, and a prcess f eliminatin. In a few cases, special methds have been wrked ut fr the separatin f certain cmmnly ccur ing mixtures, such fr instance as the three halgens, and sme f the anins f sulphur, but n the whle, little regard has been paid t cmplicatins: arising when a number f acids are present at nce. The errrs and cnfusin resulting frm the custmary methd f attack, becme particularly prnunced in the case f students first cnfrnted with the prblems f recgnizing and distinguishing between the varius negative radicals in an unknwn mixture. While they btain a fairly cmprehensive view f the relatins between the metallic elements in their reactins, this is nt true f the nn-metallic elements. As an actual fact, the student is just as likely t be cnfrnted at sme latter time with a mixture f varius acid radicals as with a substance cntaining a number f metals. The nly wrk recently published with a view t a fairly cmprehensive scheme f separatin is that f A. A. Nyes. * J. Arner. Chem. Sc (1912)

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19 -2- The fundamental idea f this methd is the separatin f the vlatile and nn-vlatile acids in varius stages b# distillatin after additin f phsphric acid. The mre vlatile acids, such as hydrcyanic acid, are cllected in the first distillate, the less vlatile in the secnd. The varius prtins are then examined much in the custmary manner, fr specific reactins f ne r the ther acid, withut attempting t effect a furthur separatin. The methd is, in many respects, ideal and very effective and a very great imprvement upn the smewhat haphazard prcedures previusly described. In cases in which the nature f the mix ture is such that interactin between the varius cnstituents is pssible, the prlnged heating during distillatin will hasten and extend decmpsitin with resulting decrease f directness r certainty in the results. The fact that each distillatin with phsphric acid entails destructin f the distillatin flask des nt invlve mre than a slight incnvenience in individual cases; where the methd is, hwever, t be applied repeatedly by large numbers f students, this fa.ctr des becme ne which it is desirable t eliminate. The part f the investigatin presented here has t d with the first grup f acids, in the fllwing classificatin, I. Anins which give a silver salt insluble in dilute nitric acid, but whse barium salts are sluble in water r acids. II. Anins whiqh give a silver salt difficultly sluble in neutral slutin, but readily sluble in dilute nitric acid, and whbe barium salts are readily sluble. III. Anins which give silver and barium salts insluble in water alne, but sluble in the presence f dilute nitric acid.

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21 -3- IV. Anins which give salts f silver and barium readily sluble under all cnditins. V. Anins which give silver sails sluble in water, but whse barium salts are insluble, even in the presence f nitric acid. The anins included in this first grup are Cl~~; Br - ; I~"; - iii jv CN ; CNS ; Fe(GN; 6 ; Fe(CN) 6 ; S 7 The first task was the cllectin f the slubility data f the anins cmbined with metals, in alkalies, acids, r ther salts; and an examinatin f thse cases wftich ffered prmise f being serviceable. In the cases f sme f the anins, it was easy t find insluble salts, but difficult t effect a separatin, due t similar prperties f sme f the anins. Other anins give but few insluble salts, and f these, a still smaller number were adapted t the purpse'iri view. In many cases, the data given as authentic in the literature, were btained under ideal cnditins, and hence were inapplicable t the present case; thus necessitating a determinatin f limits f sensibility fr every step taken, since the effects f the varius anins upn each ther were unknwn. All f the acids can be separated in different ways n the basis f the slubility f their varius salts except in the case f the cyanide, and thicyanate. These tw anins nly, yield several insluble salts. In the literature, nickel and cbalt cyanide are given as insluble, and th; ; thicyanates as sluble. These results were btained under ideal cnditins; that is, referred t pure water. But in slutins such as these, dealt with in this separatin, where either acid r alkali is always present, it was fund impssible t separate the insluble cyanide frm the sluble thicyanate by using either cbalt r Nickel.

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23 -4- The effect f the cmplicatins intrduced in the curse f analysis is shwn by the results tabulated under these and varius thei metals furthur n. II. SEPARATION OF FERROCYANIDES AND FERRI CYAN IDES. The plan which first suggested itself was t add metallic zinc t the mixture f the silver salts f the acids. The silver salts are thus reduced with the prductin f metallic silver and the crrespnding zinc salts. The zinc ferrcyanide and ferricyanide being insluble, will remain with the reduced silver and unused zinc; the remaining zinc salts are left in slutin. This methd was nt at all neat and it lst in sensitiveness as a result f the cclusin f sme f the ther anins by the metallic sil- * ver r zinc. In additin, as shwn by G. McP. Smith, metallic * Zeit. fur Anrg. Chern (1913) zinc, when acting n ptassium ferricyanide will reduce the same, and als give the ferrcyanide in the slutin. Nne f the zinc, hwever, was fund in the filtrate. This was the reasn fr sme f ur errneus results, namely, that f finding ferrcyanide, when nne wa3 riginally present. This prceedure wuld have been mre in harmny with the steps t be anticipated in the succeeding grups, since the first grups culd there be remved as a whle. It was, hwever, nt fund feasible t carry it ut in this manner. The difficulty was bviated by adding zinc nitrate t the slutin befre adding any

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25 -5- silver nitrate. The insluble zinc f errcyanide and ferricyanide are precipitated, leaving the remaining acids f the first grup in alutin, frm which they are precipitated by silver nitrate. Experiments perfrmed t determine the sentiveness f this methd shwed that in a slutin cntaining dilute nitric acid, 0.05 mgs. f ferricyanide r f errcyanide in ten cc. ttal vlume gave a decided precipitate, while 0.02 mgs. culd still be dectected by an experienced bserver. The separatin f the tw zinc salts was fund t be readily effected by means f ammnium hydrxide, and will be described under the general prcedure. Anther treatment is with scium hydrxide and ammnium nitrate, which will als be taken up later n SEPARATION OF THE REM IN IMG ANIONS. Having precipitated the silver cmpunds f CI, Br, I, S*3ST, CNS~, Fe(CN)g, Fe(CN)~, and = S, the next step was t determine upn a prcess f separatin and identificatin. A brief descriptin f sme f the prcesses tried, and the reasn fr rejecting varius nes will fllw. A. Ammnium Hydrxide. Since ammnium hydrxide is a gd slvent fr sme silver salts, the pssibility f its use fr the separatin was examined. Silver idide and sulphide were fund t be insluble under all cnditins. The slubility fi the silver salts under examinatin, differed cnsiderably under varying cnditins, which made a separatin by this methd nt feasible. Fr example, silver chlride is easily sluble in dilute ammnium hydrxide, whereas the

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27 . -6- brmide is "but slightly s, but easily sluble in cncentrated. The thicyanate ib sluble nly in cncentrated ammnia. The ammnium cyanide is als very unstable, s that even if a separatin is btained, there is danger f decmpsitin in subsequent manipulatins One f the fundamental bjectins t this methd is the unreliability f the results btained, in attempting t extract a mre sluble substance frm an admixture cntaining les3 sluble substances. This is never pssible with mathematical precisin, and, unless the differences in slibility are very great, it is nt even pssible fr practical purpses. Given large quantities f tw such cnstituents, fr instance, silver brmide and silver idide, such a methd gives decided results. But at the extremes f the range f mixtures, the results are f necessity errneus. Thus a large quantity f idide will prevent slutin f small percentages f brmides, and cnversely, small percentages f idide will disslve with the larger prtin f brmide. Methds f separating the silver halides by ammnia d nt seem t have btained wide applicatin, althugh several have been described. Fr these reasne, the methd wqs abandned after a brief examinatin f its pssibilities. B. Lead Salts. The behavir f the lead salts f this grup f acids was then studied, in an effrt t see if idine might be separated as lead idide, after the reductin f the silver salts. The fllwing table shws the behavir f lead acetate added t a neutral slutin f the anins, and in acid slutin f the anins. Behavir f Lead Acetate with varius salts (vl. 10 cc.)

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29 . -7- added t a neutral slutin f: lms. 3mg. 5ms:. 7xncr. lomg ; lmc". 3mg. 5mg. 7mer. lomg. KC1 4 f jtvtsr i T 4T J- 1 T KI f KCN "f f KCNS- t The results given in the abve table shw that this salt des nt ffer a satisfactry means f separatin, since in neutrall slutins a precipitate was btained in every case, while in an aid slutin, 7 mgs. f idide yielded nly a slight precipitate and ten mgs. nly a fair ne. Even if the lead idide separatin had been practicable, the lead wuld again have t be remved after prceeding with anther step. Such an extra step increases the liability f lsing small amunts f the acid, and is an added disadvantage in the use f lead. C. Mercurus Salts. Anther plan tried was t add mercurus nitrate t the acidified slutin cntaining the anins under discussin. The mercurus cyanide, thicyanate and idide are sluble in excess f the mercurus nitrate, r in nitric acid, while the brmide and chlride are insluble. Behavir f Mercurus nitrate. (Vl. 10 cc.) KC1 3 mg. 4 2 rag. 4 KBr mg. 4 KI Yellw ppt. disslves immediately in excess HgNC>3 r HNO3. KCN White ppt. " " " ««KCNS White ppt. " " "» n w

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31 -8- The chlride and brmide being insluble, the actin f mercurus nitrate upn the 3ilver salts f these tw anins was studied. Behavir f mercurus nitrate upn silver chlride and brmide. KC1 AgN0 3 HflWOg ppt. ppt. KBr «KI» slutin KCH blackens, slutin KCNS " slutin The chlride and brmide were each treated with ammnium hydrxide t determine if the mercurus chlride and brmide had really been frmed. The white precipitates bth blackened, shwing the presence f the mercurus salts. The first bjectin t the scheme came when it was fund that part f the chlride and brmide were als in slutin, which is just what was nt desired. The plan was finally rejected because in using mercurus nitrate, the mercury wuld have t be remved befre trying t detect fr any ther anin. This wuld necessitate the intrductin f hydrgen sulfide r sdium chlride. The cyanide was invariably lst in this prcedure, when present in small quantities. The plan f reprecipitating and redisslving the precipitate in excess was nt at all practical in this case, and was abandned after the stud y f the frmate reductin and cuprus salts had been investigated. D.' Frmate Reductin. Since zinc was fund nt t be a very satisfactry reducingagent, and after reductin, a separatin was impssible t find, ther reducing agents were examined. Sdium frmate was then

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33 -9- studied, as was als frmaldehyde and frmic acid. Freshly precipitated salts were washed free frm traces f free silver, A few drps f ammnium hydrxide were added, and six t ten drps f nrmal ptassium hydrxide, and then 0,5-2 grams f sdium frmate r several cc. f frmaldehyde and frmic acid. Theretically, ne gram f sdium frmate shuld reduce tw grams f silver chlride, cnsequently nly a small amunt f reducing agent is necessary. The ammnium hydrxide is used because it hastens the slutin f the silver salts. Reductin was carried ut by heating, the ttal vlume being kept as near ten cc. as pssible. The fllwing table shws the results btained by using the three reducing agents, frm which interesting cnclusins can be drawn. Actin f Reducing Agents n Silver Salts. (Time min.) Cmpund taken. Frmaldehyde. Frmic acid. Sdium Frmate in 5 mgs. presence f KOH. AgCl + +(rapid red) AgBr + f( slwer) + Agl + - _ AgCN f + AgCNS 4-4- (slw red) + Ag 3 Fe(CN) 6 + +(pr test) uncertain. n test. Ag 4 Fe(CN) 6 -f +( p r test) ~ (deccmp.) AgS - + It was at first thught that the frmate reductin culd be applied directly t a precipitate cntaining als the f errccyanides and f erricyanides in rder t find ut whether the precipitatin f zinc ferrcyanide and f erricyanide at the utset f the analysis culd be dispensed with. This wuld pssibly have been mere

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35 -10- satisfactry as fax as manipulatins in the suceeding grups are cncerned. Hwevern n reactin fr ferrcyanide r ferricyanide culd be btained in the filtrate frm the reduced silver. Upn examining the precipitate, it was fund that the tw cmplex cyanides bad decmpsed, if nt altgether, at least partially. Acidifying the precipitate fr. the ferricyanide with sulphuric acid, and adding ptassium thicyanate prved the presence f ferric irn. Adding ptassium ferricyanide t the precipitate frm the ferrcyanide, and acidifying, shwed the presence f ferrus irn. The breaking up f the cmplex anin wuld intrduce cyanide int the slutin, and wuld make it impssible t decide whether tests fr riginal cyanide were valid. The necessity f remving the f errcyanides and f erricyanides with zinc nitrate befre separating the ther grups by the silver precipitatin still remained. As is seen in the table, neither the idide nr sulfide were fund in the filtrate f the sdium frmate teductin. This was carefully studied and in nt a single case, has a trace f idine been fund in the filtrate. Five mgs. f silver idide were biled fr ne hur with sdium frmate, withut a trace f idine in the filtrate, whereas all the ther silver salts were cmpletely reduced in minutes f energetic biling, even in mixtures cntaining varying quantities f each. T prevent lss f the cyanide during biling, and t hasten the reductin, a little caustic alkali must be added, enugh t give a distinct alkaline reactin is sufficient. Under these cnditins, the slutin may be biled r evaprated withut mater-

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37 ial lss f hydrcyanic acid. The precipitate was then examined fr idide and sulfide, by reducing with metallic in neutral slutin. The idide was always fund t be present in this filtrate. Upn acidifying the precipitate with hydrchlric acid, the sulfide was evlved as hydrgen sulfide. The sfcdium frmate reductin has prven t he the mst satisfactry reducing agent; and nt nly that, but it has aided in the separatin f tw therwise difficultly separable anins. E. Cuprus Salts. The behavir f cuptus salts was next investigated while trying t separate the chlride, brmide, cyanide and thicyanate frm ne anther. The precipitatin f cpper as the thicyanate is a well knwn quantitative methd. It remained t be seen hw the ther ins present wuld distribute themselves, particularly when ne r the ther was present in large quantities. It was fund that in the presence f sulphurus acid, cuprus chlride and brmide remain in slutin, whereas the cyanide and thicyanate will precipitate Behavir f Cuprue Sal$s in Presence f SOg (10 cc). KC1 100 rag. sluble KBr 100 mg.» KON 100 mg. precipitates KCNS 100 mg. While wrking n this methd, a paper by L. J. Curtman and A. G. Wickff* n the same salts appeared which cnfirmed the re- * J. Amer. Chem. Sc. 37 S98 (1915)

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39 -12- sults we had btained. This paper called attentin t the interference f cyanides, thicyanates and f erricyanides in the detectin f brmides by rdinary methds, and the determinatin f this interference. They fund that they culd detect tw milligrams f brmine in the presence f 500 milligrams f the interfering substances. When the thicyanate and cyanide are precipitated, the chlride and brmide cculd be detected, but the matter f treating the precipitate presented a difficult prblem. The mst difficult prblem f the whle prcedure has been the separatin f this precipitate. Varius salts such as ammnium chlride, ammnium sulfate, sdium thisulfate, nitric acid were tried in rder t find 6ne which shuld, disslve nly ne f the tw, but withut success. Finally the fllwing prcedure was adpted; a few drps f nrmal ptassium hydrxide were added t the precipitate and diluted with 3-4 cc. f water and hee.ted gently, and then diluted t ten cc. The cuprfcus salts are decmpsed giving a precipitate f cuprus xide, while the cyanide and thicyanate pass int slutin. The cuprus xide is filtered ff, and the filtrate is treated fr cyanide and thicyanate. It was fund necessary t remve the cpper cmpletely befre the test fr the presence f cyanide culd be made. Its presence interferes with the cnversin f the cyanide int the ferric ferrcyanide r Prussian blue. When cpper was present in a knwn amunt f cyanide, instead f Prussian blue, a red precipitate which was prbably CugFe(CN)g was frmed. This seemed t be frmed in a small amunt cmpared t the amunt f cyanide present. It is quite essential t remve the c&pper, but a large e; cess f alkali shuld be avided s as

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41 -13- nt t disslve any f the cpper. Fr increasing the sensitiveness f the ferrcyanide reactin, the additin f ptassium fluride as advised by A. Vicheuer and C. 0. Jhns* was used. It must be nted, hwever, in this cn- J. Amer. Chem. Sc. 3? (1815) nectin that the sensitiveness f th& reactin fr ptassium thicyanate, which is t be determined in the same slutin, is destryed. Thus a red ferric thicyanate slutin can be cmpletely bleached by sufficient ptassium fluride. The actin f ptassium xalate and phsphate was tried, but they had n effect like the fluride. Since the delicacy is increased in a platinum dish as well as in a glass tube, the reactin cannt be slely based upn the frmatin f a flusilicate, althugh the actin n a test tube wuld lead ne t think that the frmatin f the flusilicate was an imprtant factr.

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43 IV. PROCEDURE Precipitatin f Ferricyanides and Ferrcyanides Prcedure I. Add ne t three cc. f dilute nitric acid t a neutralized mixture acids, and then enugh zinc nitrate t insure cmplete precipitatin f the ferricyanide and f errccyanide. Cmpleteness f the precipitatin is indicated by a nticeable change in the character f the precipitate which is cllidal at first but cagulates mre readily when excess f precipitant is present. When sufficient ferricyanide is present t clr the slutin, there is a fairly sharp end pint, cnsisting in the discharge f the yellw clr. When nt enugh zinc nitrate is present, the slutins are cllidal, an excess f zinc nitrate t insure cmplete precipiattin f the ferricyanide and ferrcyanide being advantageus. 1-2 grams f ammnium nitrate hasten cagulatin f the cllidal precipitate. In the cmplete absence f ammnium salts, the zinc precipitate was fund t remain cllidal indefinitely. Heating f the slutin shuld be avided, since it increases the tendency f the precipitate t becme cllidal, and wuld cause lss f part r all f the hydrcyanic acid. Ageing seems t favr the separatin f the precipitates. Shuld the precipitate run thrugh the filter, which fr this case shuld be a fairly clse grained filter, it shuld be set aside fr a shtt perid when the precipitate usually will be fund t have changed sufficiently t permit satisfactry filtratin. The same effect may be btained mre rapidly by shaking the suspended precipitate ener-

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45 -15- getically in a stppered flask. This is, in effect, simply the ageing f the cllid and is very effective in prducing a precipitate which des nt run thrugh the filter. (a) After washing the zinc precipitate n the filter several times with a few cubic centimeters f a dilute ammnium nitrate slutin, (rejecting all but the first washing,) pur ten cc. f a warm 3$ NaOH slutin nth rugh the filter. This sufficient fr quantities up t 200 mg. f each f the tw salts, which disslve, yielding the alkali ferri- and ferrcyanide and sdium zincate. Add t the resulting slutin 5 cc. f a 5$ ammnium nitrate slutinand shake vigrusly. The zinc ferrcyanide is precipitated as a gelatinus white precipitate. This precipitate is quite characteristic. It may, if desired, be furthur characterized by the cnversin int the cupric r ferric ferrcyanide. The red cupric ferrcyanide is t be preferred since it is just as sensitive and cannt be cnfused with the ferrus f erricyanideaas the ferric ferrcyanide may. In either case, the ferrcyanide f zinc is disslved in a small quantity f NaOH slutin, the cpper r irn is added and the slutin then acidified. This is preferable t acidifying first, particularly when nly small quantities are present, since the zinc ferrcyanide when nce frmed, is nt cnverted int the cpper r irn salts very rapidly. * The character f this precipitate is particularly well adapted fr quantitative apprximatin. A series f seven precipitates btained in the regular curse f analysis. and varying frm 100 t 1 mg. in apprximately even steps, were crrectly estimated by fur ut f five bservers entirely unused t the methd.

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47 -16- (b) Anther methd which was used, largely thrughut this wrk, and gave very satisfactry results, was based n the slubility f zinc ferricyanide in ammnium hydrxide. The precipitate f the ferri- and ferrcyanide f zinc is first treated with ammnium hydrxide and then washed. The remaining precipitate, the ferrcyanide, is then disslved in sdium hydrxide. When the tw anins are thus separated, the cnfirmatry tests fllwing may be applied. This methd, while gd, has an extra step cmpared with the previus methd. Since in the previus methd, the whle precipitate is immediately disslved, in caustic alkali, and the separatin then effected by precipitatin. The ferricyanide is identified by acidifying the filtrate frm the zinc ferrcyanide (frm a) with dilute hydrchlric acid, and adding 1-3 cc. f ptassium idide slutin(this shuld nt give free idine upn acidificatin ), and 0,5-lcc. f CHCI3 r CCl^. The ferricyanide is reduced, giving free idine in the CHC1 3 layer. 2 K Fe(CN) 6-2 KI 2 K4 Fe(CN) g - Ig A ferric salt gives with a ferrcyanide a blue precipitate f ferric ferrcyanide, but nt with ferricyanide. A ferrus salt gives with a ferricyanide a similar blue precipitate f ferric ferrcyanide. It gives with ferrcyanide a white precipitate f ferrus ferrcyanide, when n ferric salt is present, but turns blue in the air. In rder t test fr the ferricyanide with a ferrus salt the slutin must be fresh, that is, free frm ferric salt. In using this as a test fr the ferricyanide, ne is nt always sure whether the precipitate may mt have been due t a. trace f ferric irn, which wuld give a similar pre cipitate with ferr-

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49 -17- cyanide. The reactin with ptassium idide is t be preferred fr this reasn. When applying this test fr small quantities, it is necessary t bear in mind that cmmercial iddides cntain usually, traces f idates and will cnsequently give traces f free idine n acidif isaticn. A reagent which will nt liberate free idine upn acidificatin may very cnveniently be made by biling a neutral, r but faintly acid, slutin f ptassium idide with metallic magnesium. The xidatin f idides by f erricyanides is slw, and in testing fr small quantities, time must be given fr the idine t be liberated. As in the case cf f errcyanide,a fairly accurate estimatin can be madewhen amunts frm mg. were used by ne unused t this methd. The results btained during experimentatin n the abve separatin are given in the fllwing tables. Sensitiveness f test with zinc nitrate in presence f dilute HNO3. (vl. 10 cc.) mgs K 3 Fe(CN) f Z 4 Fe(CN) Zinc Ferricyanide Reactin. Reliability in presence f the ther substances. (vl. 10 cc.) In Presence f 200 mgs. f: 0.0 mg. O.tf rag. 0.2 mg. 0.5 mg. 1 mg. KC KEr - + -!-++ f KI - + KCN KCNS 4-4. J. 4. K 4 Fe(CN)

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51 -18- Zinc Ferrcyanide Reactin. Reliability in the Presence f the Other Substances. (vl. 10 cc.) In presence f 00 mgs, f mg. 0.2 mg. 0.5 mg. 1 mg. KC1 ± KBr KI KCH KCNS K 3 Fe(CN) Prcedure II. The filtrate frm the zinc precipitatin is treated with silver nitrate until precipitatin is cmplete. If cyanides are present a furthur indicatin f the cmpleteness f precipitatin issbtained by the disappearance f the dr f hydrcyanic acid. When a slight excess f silver nitrate has been added, shake the precipitate t cagulate it. Filter r decant and wash twice, cllecting the first washing with the filtrate, which cntains the a- cids f the succeeding grups. Wash the precipitate at least thtee times mre, r untiil n silver is fund in the washings. Prcedure III. Transfer the precipitate t a beaker and add 1-2 grams f sdium frmate, (the amunt taken will depend n the quantity f precipitate taken, hwever ). Add three drps f dilute ammnium hydrxide and then 5-10 drps f nrmal caustic alkali. Add water t make a vlume f cc, and bil vigrusly, keeping the vlume the same during the reductin. Reductin is cmplete when there is n silver left in the slutin. The time re-

52

53 , -19- quired is generally frm minutes. When tmmuch alkali is used, there is a tendency fr the silver t becme cllidal, and very difficult t reduce. Prcedure IV. The slutin is filtered ff and the precipitate is washed twice, cllecting the first washing with the filtrate. The precipitate is transfered t a beaker, and grams f zinc is added. Allw the reductin t take place in neutral slutin. If any idide is present it will pasn int slutin as zinc idide and may be identified in the filtrate by several characteristic tests (a) Pur ff the slutin frm the zinc reductin, filtering if necessary, als saving the precipitate fr prcedure five. Acidify with 1-3 drps f dilute acetic acid, and add ne t tw drps f thallium nitrate. A yellw precipitate f thallium idide frms, which is quite characteristic f idine. The fllwing table shws the limits f sensibility with and withut intervening reductin. Behavir f Thallium Nitrate in Presence f Idide. (vl. 10cc mgs. f N intervening reductin. KI. 5 mg. 3 mg, 0.5 mg. 0.3 mg. 0.1 mg. 0.05mg With intervening reductin. f (b) Anther delicate test id the xidatin f the idide t free idine by any f the custmary methds. The reactin between ferricyanide and an idide in the presence f an acid has prven very satisfactry. Acidify the filtrate cntaining the

54

55 -20- idide (frm divisin a) with 1-2 cc, f dilute hydrchlric acid, add 1-2 mgs. f ptassium f erricyanide, and cc. f chlrfrm r carbn tetrachlride. Shake thrughly and if any idide is present, idine will be liberated. This test has been fund sensitive t 0.02 mg.with a gd degree f certainty. With small quantities f idine, the clr develpes slwly. The precipitate frm divisin (a) cntains the insluble zinc sulfide. Transfer the precipitate t a test tube with ne t tw cc. f water, acidifying with 1-3 drps t dilute hydrchlric acid. If any sulfide is present, hydrgen sulfide gas will be evlved, which may be easily cnfirmed by hlding a piece f filter paper saturated with lead acetate ver the muth f the test tube. A blac k precipitate f lead sulfide will be due t the actin f the hydrgen sulfide. Prcedure V. The clear filtrate frm prcedure (4) cnatining the chlr- 3 ide, brmide, cyanide and thicyanate is heated t biling! Any silver in slutin will cme dwn, and must be rejected unless the quantity is large in which case it is added t the remainder f the silver reductin. Tb prevent lss f cyanide, the slutin must be kept alkaline all the time. The ht slutin is nearly neutralized with dilute sulfuric acid, and five t fifteen cc. f saturated sulphur dixide slutin are added. Then with cnstant stirring cpper sulfate is slwly added until an excess is present. If ther e is nt enugh sulfurus acid, the slutin may be green,, * It is unnecessary t bil the slutin. * If a white precipitate frms here, it is silver, and is present due t the cmplete reductin with sdium frnnate and may be rejected.

56

57 -31- due t the fact that sme f the thicyanate is still unccmbined with the cpper. While still ht the slutin is filtered. Unless thrughly cagulated, the precipitate has a tendency t run thrugl the filter, hence a clse grained filter is necessary. The precipitate shuld be washed with ht water, and the first washings cllected with the filtrate. Prcedure VI. The precipitate frm prcedure (5) cntains the cyanide and thicyanate. Transfer it t a beaker with water, making a vlume f ten cc. Add caustic alkali r carbnate t precipitate the cpper, allwing the anins t pass int the slutin. 1-4 drps f nrmal ptassium hydrxide shuld be sufficient. A strng slutin f alkali wuld interfere seriusly with the delicacy f the cyanide test. If present in" fair quantity, say 5 mgs., the cyanide and thicyanate may be separated by cnverting the cyanide int Prussian blue and filtering. Adding ferric chlride t the alkaline slutin causes Prussian blue t precipitate in flcks at nce when acidified, instead f the usual preliminary cllidal frm. The red ferric thicyanate will be in the filtrate, while the Prussian blue will be n the filter. When nly small prtins f either anin are present, half f the slutin must be taken and tested fr the presence f each anin. When this is lne, ptassium fluride may be used t advantage in testing fr cyanide since a separate prtin is t be tested fr the thicyanate. Prcedure VII. The filtrate frm prcedure (5) cntains the chlride and brmide anin. Bil the slutin until free frm fulfur dixide until a vlume f 5-10 cc. remains. A precipitate frming here may be rejected, since cuprus chlride is quickly hydrlyzed by

58

59 -33- ht water t cuprus xide. Biling is mst cnveniently carried n in an Erlenmeyer flask, t insure against less, (a) Filter ff the cuprus xide and pur the filtrate int a test tube. Acidify with 1-2 cc. f dilute sulfuric acid and add 1 cc, f 0.1 nrmal ptassium permanganate. After shaking a few secnds, cc. f carbn tetrachlride is added. Cntinue the shaking and if a yellw clr appears in the tetrachlride, brmine is present. (b) T test fr chlride, dra?/ ff the liquid prtin frm (a), and add frm 15 tp 30 cc. f the permanganate slutin. If nt already sufficiently acid, mre sulfuric acid is added. Bil this slutin fr 5 minutes, r until n furthur brmine cme 3 ff, and the vlume is dwn t 10 cc. The manganese dixide is filtered A. A. Nyes. J.Amer. Chem Sc , (1913) ff, and if the filtrate is pink, a drp f sulfurus acid will destry the clr. Dilute the slutin tc 50 cc, add 1-2 cc. f dilute nitric acid, and ne drp fl nrmal silver nitrate slutin. A white precipitate shws the presence f chlride. (c) Anther methd f detecting the brmide, withut taking the first step f disslving the xidized brmine in carbn tetrachlride, is the uie f flurescin paper. In this manner the brmine can be detected at the same time that the cmplete xidatin f the brmine fr the chlride test is taking place. Filter paper, dipped in a cncentrated slutin f flurescin in acetic acid is held ver the vessel frm which the vapr is cming. Traces f brmine are shwn by pink streaks, due t the fmmatin f ebin. This methd is nt applicable fr a mixture f free brmine

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61 -23- and large amunts f free chlrine. But in a mixture f chlride and brmide, the methd is very delicate, and the brmine can be liberated by means f ptassium permanganate. Cmpt. Rend (1897) Abe. J. C. S. II 133 (1898) Since any cyanide that might be present is vlatilized, and the brmine can all be xidized, it was thught advisable t find ut if the thicyanate wuld have any effect upn xidatin with ptassium permanganate in case any were in slutin. Prtins f 30 and 40 mgs. f ptassium thidyanate were treated with c.f ptassium permanganate slutin, and acidified with 1-2 cc. f dilute sulfuric acid and biled. The MnOg was filtered ff and the filtrate was tested with ferric chlride, but withut result; als by acmifying sme f the filtrate with dilute nitric acid and adding silver nitrate, but n precipitate was frmed. The thicyanate, if any were pssibly present, wuld nt interfere with the chlride test, as has als been shwn by A. A. Nyes. * J. Amer. Chera. Sc (1912) The general cnclusin is that if this test ie carefully cnducted, it shuld hld gd fr chlrides t a very great degree f delicacy in presence f the cyanide, thicyanate, and brmide, as is shwn t be the case. The fllwing table shws the limits f sensitiveness fr each $est f an anin, in absence f the thers. Each anin was treated thrugh the whle scheme f analysis, in the amunts given at the tp f the table. Each analysis wa3 cnducted in triplicate and since results checked s clsely in mst cases, an average,

62

63 -24- r cnly ne result, will be tabulated fr a given amunt f anin. Sensibility f Each Anin in Absence f Others Carried thrugh the Scheme. 10 mg. 5 mg. 1 ing. 0.1 mg mg mg KC1 + + KBr KI KCN -f KCNS + 4" + H" K 3 Fe(CN) f + 4- K 4 Fe(CK) J The interfering influence f ther cnstituents was then determined by taking nce, twice, five and ten times the minimum a- munt f an anin that culd be detected alne; in the presence f 200 mg. f each f the ther anins. The fllwing tables will shw the effect f large quantities f ther anins upn small a- munts f an anin. Behavir f KC1 in Presence f 200 mg. f the Other Anins, Carried thrugh the Scheme. Amunt in Presence f: 0.0 mg. 0.1 mg. 0.2 mg. 0.5 mg. 1 mg. 200 mg. KBr f KX - -I- + " KCN - -h » KCNS - -I- 4- +» K Fe(CN) it K 4 Fe(CN)

64

65 ... S. -bi5ena,vir 01 KCNS in Presence f OX XI uuiier Anins; arriej. xnriign n e Scheme Amunt in Presence f: PHD wrr TTP1 _ 0.0 mg. 0.1 mg. 4- n ITT?-** + t" 0.2 mg.»5 mg. it 1T 1 mg. T T It FT + I T" tl VP TOT 4- i 4" I "T" 1T l T _L T " 1\ R" TTp ( ~ X1 C + \ V> III J Ci i T" K 4 Fe(CN) T J_ T Behavir f K 3 Fe(CN) 6 in Presence f 200 ^F "Hie "h a t Anins, carried thrugh the Scheme Amunt in Presence f: 300. mgs. KCl 0.0 mg. 0;1 mg mg mg " KBr + + 4" 4-1 mg. i 4- it KI + + T _L 7 it tt KCN + 4-» KCNS + 4- it T»' K 4 Fe(CN) i T Eehavir f K 4 Fe(CN) 6 in Presence f 200. mgs x ne uuner Anins, Carried thrugh the Scheme Amun t in Presence f: 200 mgs. KCl 0.0 mg. 0.1 mg. * 0.2 mg. + KBr mg 4. it 1 mg. T i T «KI 4-4- i» KCN + 4- T T " KCNS t 4- J_T T i 4- i T " K 3 Fe(CN) 6 - +> + 4-

66

67 C. *"> ^ Behavir f KBr in Presence f 200 mgs. f the Other An 1 dt\ n Pq t»i»i 'l "t". Vi y* mi crv) Vi p i\ieou.n 111 Presence OUU "ig. f: IvUi. 0.0 mg. 0,1 mg. 0.2 mg. - - f~ i 0.5 mg. 1 mg. A "T 11 V"T JL. 1~ J_T 4_ i i T" it KCN J_ ) " KCNS + + & J_ T"» K 3 Fe(CN) " TfiiFp f f!ttl «- + t 4- Behavir f KI in Presence f 200 mgs.f the Other Anins, vdl J. it-a w 11 Jt UU^li 11 Scheme Presence f: 200 m- KCl 0.0 mg. 0.1 mg mg. 0.5 mg. 1 mg, + + ti xrvir _ _ " KCN " KCNS f 4- K 3 Fe(CN) f + K 4 Fe(CN) fr- 4- Behavir f KCN in Presence f 200 inge. f the Other Anins, Carried thrugh the Scheme Amunt in Presence f: 0.0 mg. 0.1 mg..2 mg. 0.5 mg KBr 4- + " KI KCNS f + + " K Fe(CN) mg. + K Fe(CN)

68

69 -27- O CVJ M CO CVJ CO CVJ CVJ ih O CS3 to O CVJ t O <D -P Pt w rh csj H CO O CO O CO u O t m CVJ CVJ H 1 rh ih m n S3 rh rh t<3 rh I lo CO p CO u +> ca p u H <H fl O O CO Cvl (3D CO a 5 t cq t CO CO <D K t O S3 60 +> Pi ft «c* a> CO CO

70

71 -28- H O CO CO ih O CO 8 a 4* 1 CO O w HO r< +> C\J M 0) a S CO tb -P It ft a cc CO H H <D 00 ft C\2 i CO ft rh 6 1 w EH 03 O H H O CVJ rh rh 1 Ol T! CV2 1 rh t 3 CO ft u tj CVJ I w CO ft rh T< I rh CD ft CO ft <» P4 CO CM W p t H CO w CO ts3 p* H rh CO CO fh CO +3 CD P< rh CO 1 K in

72

73 I 5h pq 54 5-t O >s rh 05 O H O & rh O rh O H ) «>s-h & CO CO S3. B S3 B J? c ^ S3 f-i t t S3 PS rh,0 C\2 <D CO -p CO P «H P S3 rh CO M <D 5-1 rh CO O O -P PhH -P CO 03 CM O 3 u CD rh Q> O «H rh a 1 t CVJ O CO e Ss <D CO re H O PQ O O Cv2 CO W f O rh ^). O S3 a E u t rh CO» rh 1 O -p rh rh O O S H O in CO rh rh p> H H O O O 1 i w p 1 O rh 03 rh G\2 >H 5-i +3 ft ft -P 5h 1 -P rh t ^ rh OJ rh H 1 «H rh rh H (H t 125 ft O?-«

74

75 IV. EXPERIMENTAL Stek slutins, ctaining varying quantities f each anin, as shwn in table N. I, were made up fr analysis. The scheme f analysis just utlined, was used thrugh ut. These slutins were labeled by an utside party, thus leaving ths cntents f each slutin unknwn. In the first analysis cnducted, there were errrs in manipulatin, which resulted in the lss f the cyanide. The result f the first run f analyses is shwn in table H. II. In every case, 50 cc. f the stck slutin were taken fr each analysis. Table N. III. shws the results btained by analysis, f the same slutins when all the prpsr precautins were taken. In practically every case it was pssible t judge the amunt f anin present frm the amunt f precipitate frmed. Especially is this true f the ferricyanide, ferrcyanide, cyanide and thicyanate whse precipitatin is practically quantitative when the scheme is carefully fllwed.

76

77 -31 ind 32- CD to O ph t 0} 03 O O O CO O PM PM PM Si PM PM * to O CM Pi hq CO O O O O Sh PM 5 PM PM PM PM O O t-i CD Ph Ph ttio to 03 O O O CO O PM PM PM PM PM 03 CO M EH E> PI O CO Eh CO M O CV2 O ih O rh O CD O CD O < O O CO M M CO >H PI a pi <»< M «EH EH CO «M 03 bo CO I O CO \ O O PM PM PM PM 03 O PM 03 O PM CO 03 CO EtO 193 t 03 O O CO O PM PM PM PM PM M M O t 03 CQ{ 03 cl O CO O O O O O O PM Ph 1 PM P-il PM PM CD t CM Ph O O CD O t cvj O H PQ t t 03 t O O O CO O CO PM PM PM!2i h PM 525 CD t c\j O O O O O O O PM PM PM PM PM PM PM 1 1 t t t t 03 I? M M S3 t CO Ph Ph t 8 W S2J S25 CO CO 3 Ph P^ O tq ^ M M M

78

79 CO O O CD O O O Ph Ph EH ft Ph Ph Ph t 03 cl O O CD O O Ph Ph &5 Ph Ph Ph t t O O O CD CD O O Ph Ph S3 ft Ph Ph 03 t CO O CD O O O Ph ft Ph Ph Ph Ph Ph ft t 09 O O O CD O Ph Ph Ph Ph Ph ft Ph t I CD O O O O O ft Ph Ph Ph Ph Ph Ph cq t O O O O CD Ph Ph Ph Ph Ph Ph O O O O O O Ph Ph Ph Ph Qh Ph Ph 03 52! M ft t ft O CO CD CD 3

80

81 V. SUMMARY In this investigatin a methd f separatin has been wrked ut, fr thse anins whse silver salts are insluble in dilute nitric acid, but whse barium salts are sluble in water and acida. The ferricyanide and ferrcyanide are first precipitated as the zinc salts. The remaining anins are precipitated as the silver salts in an acid slutin. The silver salts are reduced in an alkaline slutin by sdium frmate. This leaves the idide and sulfide in the precipitate, frm which the idide is btained thrugh zinc reductin, while the sulfide test is btained by acidifying. Frm the filtrate the cyanide and thicyanate are precipitated as their cuprus salts. The precipitate is treated with dilute caustic alkali and the anins are disslved while the cpper is precipitated, thus aviding the interfering actin f cpper. The chlride and brmide cntained in the filtrate f the cuprus precipitatin may be separated by xidatin with ptassium permanganate, r any ther cmmnly used methd.

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84