A CORROSION COMPARISON OF SEV- ERAL METALS USED AS CATHODES IN ELECTROANALYSIS BY KDWIN HERBERT WEBSTER THESIS FOR THE DEGREE OP' BACHELOR OP' SCIENCE IN CHEMICAL ENGINEERING COLLEGE OE LIBERAL ARTS AND SCIENCES UNIVERSITY OF ILLINOIS 1922 Digitized by the Internet Archive in 2015 https://archive.org/details/corrosioncompariOOwebs 1322 \Y39 UNIVERSITY OF ILLINOIS i 922.__ THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY .Eilwiii _ KeiLuBX t_ ex ENTITLED A-0-Q.rxQ£lia2i-JlQiipxD:i F. on -nf. J5£-xex£JL-Y-ntiilp- -JIl££.C— a.s-CAtl-Qjlea--iji-ni£ij.txQa.nal^sx£^ IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF 3acLelQr._jaf_^ci-enae.__jLii-_CLeiLlcLLL_Xii^ijiBj£ij:'j_ag HEAD OF DEPARTMENT OF CLemisiry. TABLE OY COIfTEBTS page I. IITTPOPIJOTIOU 1 II. EISTOEICAL 2 III. EZPEBE^ITTAL 4 1 . Material 4 2. Procedure and Piagrem 9 IV. EESULTS 11 1 . Silver Eitrate Solutions 11 2. CJoLalt Sulphate Solutions 11 3. Colalt Eitrate Solutions 11 4. Eiekel sulphate Solutions 11 5. Eickel Eitrate Solutions 12 6 • Oopper sulphate Solutions 12 7. Copper Eitrate Solutions 12 8. Zinc Acetate solutions 12 V. PI SCUSSIOE 14 VI. Sm2I/.EY 19 VII. BIBLIOaBAPEY 20 "i» , ' 'MV, ,1 ,■ ' ■• , y 1 ii f ’ ' '-.s^ ’* ^ »i.* ' AOMOV/IEDGMIEITT I v;ish to express my appreoi&tion to It. G-.I. Be&l and to tliank Mm sincerely for the many suggestions and aids given during' the preparation of this thesis. PART I IHTEOPUCTIOH Tliere is little materir.1 available in the literature from from which a suitable comparison of the various metals ordinarily used for cathodes in electroanalysie may be drawn. The few studies that havie been made are referred to in the bibliography and discussion; however, it was desired to learn something of the behavior of these metals when a series of quantitative electro- analyses were performed under identical conditions. This was done by studj^-ing the successive losses by corrosion of a set of cathodes of the various metals used in precipitating the five metals commonly determined in the elementary state . Prom the data obtained it is to be noted that there is, in general, a superiority of one metql over another for the purpose. PART II HISTORICAL Rroffi the empirical state of affairs common to ever^' neYJ ■branch of science the chemistry of electroanalysis has "by reason of prolific investigation become fairly definite and well organiz- ed. However , there are phases in its application that are as yet undeveloped and insufficiently investigated. Hollowing the discovery by Uicholsen and Carlisle in 1800 of the decomposition of water by the electric current, Cruik- shank observed the separation of metallic copper, and suggested the galvanic current as a qualitative agent for the determination of the metals. The discovery of galvsnoplasty , known as electropit ting, a technical process closely allied to electroanalysis , dates from 1859, as made by Jacobi. Since then many investigators, prominent and unknown, have 1 observed the electroljT-tic behavior of solutions of the s^lts of the various metals from the standpoint of the chemistry of the deposited metal. At first qualitative, then quantitative, the work has been extended to all classes of solutions, and to in- clude many of the known metals, and also a few of the nonmetallic elements . Attention of investigators has been largely dravm to the chemical reactions of the electrolytic cell, the metals suited to electrolytic deposition, the best solutions, and the proper -3- su'Dstances to "be adde^ to tlrjese solutiozis, whereas the source of the current, the physical conditions of the experiment, and the electrode mFiterials have not been fully investigated, the last only c casually hy investigators in related fields. For a period, now on the wane, it was "believed that all elements could "be determined electrolytically ; this belief natur- ally stimulated research on nearly all the known metals, and nonmetals. In the coursemof this there were investigated and de- veloped, the current sources, the vessels, the stirring devices, and simultaneous operation on many samples, however, there has been practically no work specifically on corrosion of electrodes by the electrolytes used in common electroanalytic practice. The Division of Analytical Chemistry of the University of Illinois has been desirous of obtaining some criteria of the metals in common electrode use as to their resistance to corrosion in solutions of salts of the metals commonly determined electro- lytically. There has been no previous work done along this line at the University of Illinois; this problem was taken up in 19E0 at the suggestion of Dr. G.D. Beal with a view to obtaining in- formations along this line. -4- PABT III FXPPHBTITTAL 1. Materiel In the successful completion of an investigation such as this it is necessary to use metals whose salts m.ay "be obtained in forms which are easily and accurately determined, and of such a nature that comparable results may be obtained. To this end chemically pure silver nitrate, copper sulphate, copper nitrate, cobalt, sulphate, cobalt nitrate, nickel sulphate, nickel nitrate, and zinc acetate were Tised. The silver nitrate was 99. 98^- pure as tested by the average of three electrolytic determinations. Both the copper nitrate and sulphate contained iron, approximately 0.08f^', v''hich was removed from them by ammonia precipitistion of each sample, giving a solution containing in addition tb the cop- per salt, armnonium nitrate and sulphate, respectively. Similarly each solution of cobalt and nickel was freed from iron, for though iron does not interfere seriously with electrolysis of ammoniacal solutions, it is bothersome, and may cause results to include some mechanical error. All chemicals used were of either the J.T. Baker or Baker 8 Adamson make. The concentration of all solutions used for the deposi- tion was ascertained b^/ strictly chemical as well as electrolytic methods, and the results compare very satisfactoril37. The con- centration of stock solutions was a variable, 0.003 to 0.005 g/cc of metal being the rule, save for the copper and Kinc solutions; the concentration of the copper solutions was appror.imetely 0.003 g/cc, and that of zinc 0.015 g/oc, expressed for the metals* A description of the standardization of these solutions follows: Silver filtrate 25cc portions were analyzed graviwetricf'lly hy pre- cipitation as silver crloride; the five determinations gave results of 0.1571, 0.1578, 0.1580, 0.1578, end 0.1677 grams of ^gCl respec- tively. The average of these corresponds to a concentration of 0.11876 g/25 cc of 0.00475 g/cc of silver'. Copper Sulphate 25 cc portions were analyzed hy the low iodometric method as described by Treadwell-Hall^ for sodium thiosulphate standardization; the sodium thiosulphate was strndardized against C.P. copper. Four of these portions required, respectively , 1£.78, 12.78, 12.78, find 12,80 cc of a solution of sodium thiosulphate having a copper equivalent of C. 006249 g/cc. This gives the value of the copper sulphate solution as 0.0021975 g/cc of copper. Copper titrate Similar determination of copper in this solution gave the concentration as 0.0041156 g/cc of copper. I?ickel Sulphate determination of the nickel as nickelodimethyl- glyoxime in 20cc samples gave weights of the glyozime , amounting respectively , to 0.2910, 0.2912, 0.2909, 0.2913, and 0.2911 from the average of which the concentration of the solution was deter-.- mined to be 0.002965 g/cc of nickel. ITickel litrate Similar an al yses of i i ( V \ ‘i i LI - 6 - average value of concentration as 0*0029146 g/cc of nickel. Cobalt Sulphate The cohaltie hydroxide wae precipitated hy sodium hydroxide and bromine, was ignited, and reduced by hydrogen, in 8 Eose crucible, to metallic cobalt. this method 26 cc sam- ples of the stock solution gave 0.1476, C.1475, 0.1476, 0.1474, and 0.1476 grams of metallic coba.lt, corresponding to a solution concentration of 0*005900 g/oc of cobalt. Cobalt nitrate Similar treatment of 25cc samples of this solu - tion gave an average value of 0*1372 grams of cobalt, correspond- ing to a concentration of 0.C05486 g/ce of cobalt. "ine Acetate The zinc solution was analyzed by precipitation of zinc carbonate, and careful ignition of this to the oxide. Five determinations gave 0.1862, 0*1863, 0.1867, 0.1861, and 0.1864 ‘ grams of the oxide, respectively, corresponding to a concentra- tion of 0.006989 g/ce of zinc. by electrolytic analysis the following results ?/ere obtained; Silver titrate 26 cc portions, electrolyzed according to a method £,iven in Classen-Eall gave a concentration of silver of 0.004749 g/ce of silver, an average of four close checks. II ■1 a i - 7 - Oopper Sulphate S5 oc portions, when electrolyzed, eccording to s method given in Classen-Hsll^®’ gave 0.00320 g/co as the concen- tration in terms of copper. Copper ITitrste 25 cc portions, to which v/ere added 2cc of SIT H^SO^ and 2 drops of SU ECl,were filtered free from contaminating AgCl, and diluted to approximately 75 cc; to each was added 5 cc of con- centrated E2T0g and one gram of urea. They were electrolyzed at 0. 7-0.8 amperes and 3o0.3.5 volts for 80 minutes. The deposit of metal was dried oy an alcohol wash, followed oy the burning off of the alcohol. This is the method as used by the Division of Analytical Chemistry of the University of Illinois, and the con- centration found was 0.00410 g/cc of copper. Uickel Sulphate . This solution, analyzed according to the method given by Classen-Hall^ , modified fi>r the presence of nitrates, shov/ed a concentration of 0.002911 g/cc of nickel. Cobalt Sulphate The method for the determination of cohalt paralle that for nickel, and the same method was used as for nickel. The concentration found v/as 0.005904 g/cc of cobalt. Cobalt nitrate A concentration of 0.005478 g/cc of cobalt was ob- tained by a method identictll with that described for the nickel nitrate r ji ■ ' ■ ■ i • ' ■'"' aJ • ’i f • w. I ' i} \ . t OU.I ^O' - 8 - Zino Acetate The analysis ¥/as carried out according to Olassen- Eall^in acetic acid solution. 1 cc =* 0o00597 g/cc of zinc. A comparative chart of the chemical and electrolytic standardizations of the salts employed, e:^pressed in grams of the metal per cc of the solution follows: AgEO^ CuSO/ Cuno.,: EiSO/ EiEOr. Chemical 0.C04750 0.0031955 0.0041136 0.00E965 0.00E9I45 Electrolytic 0o004749 0.00320 0.00410 0.002960 0.002911 O0SO4 C0EO5 ^nfCgEsO^)^ Chemical 0.0059 0.005488 0.005989 Electrolytic 0*005904 0.005478 0.005970 The values obtained by electrolytic analysis have been assumed as correct, because they are subject to exactly the same errors as occur later in the corrosion tests, compensating these. This work was all done on a special electrolysis setup, diagrammed on the following sheet, with stationary platinum cathodes of gauze, and rotating wire spiral anodes, in 2oocc flat bottomed EonSol beakers. ' 1 ,* tj' ■ i . I n -i. j r Y : I '> • , ■i' . - 9 - DIAGRAi: OF TEE EIEGTEIGAL GOIETECTIOES FOR TEE TE^T ELEGTROLYSES. CATEOEES STATIOEAEY'i AEOEES ROTATING. A. A . TRil A ■ — a 1 TEE EIAGRA ^ / 4 ' 1 I Z OF THE " / * 1 SETH? FOR T y • !0 t TEE ST:l ' / f P 1! TIORARY n *■ P ELEGTROLY SES IS EE/iGTLY SPAILAR. LEGERD: A Ammeter Tf Voltmeter RHIAPJCS: An £.mmeter for encE circuit, and one voltmeter connected with all or any of the five circuits, was the scheme used for as near?uy uniform conditions of electro- lysis as possible. - 10 - PAST III EXPERII.IESTAL ) 2. Procedure The tests were made ’oy the parallel analysis of five equal portions of the seme stock solution, at identical voaLtages and current strengths, for the same lengths of time. Five "runs" were made on each reagent, and assuming the complete deposition, after the proper tests v/ere made, the loss in weight of the elec- trode was calculated from its last previous ?/eight, alone. The electrodes save the silver one, were cleaned hy nitric acid of a density pf 1.20g/cc.The silver one’ was cleaned hy means of con- centrated hydrochloric acid and hydrogen peroxide. All drying of electrodes was done at the temperature range of 100°-106°C for one half hour, this having been found in all cases, to "be suf- ficient for the present investigation, vdth no accompanying danger of oxidation of the metals. The time of the electrolysis was without exception one hour for the stationary work. In the case ' of the cobalt and nickel electrolysBs there was added- to the mixtur C.P. ammonium sulphate, to increase the conductivity of the solu- tion. The electrodes used for investigation were of gold gauze, pla-tinum sheet, platinum gauze, "Palau" sheet, and silver gauze, for the revolving anode worla For the stationary work a gold dish, a silver dish, and two of platinum were used, each with a platinum sheet anode, suspended by platinum wire into the elec- trolyte. These are the common metal electrodes as used in the laboratory of the pivision of Analytical Chemistry of the Uni- versity of Illinois. I . '1 ;C,, ,y; r'-rSii ’ A t U*S • *^v'a ./;.LI 'C'?v£ «: f> ■> (-?■ •MiS:>4 I' '■ ■ ■:m ,! Ji l\l' KV >- •■ 1 ■• r*li-' V"i - .. |l ■'’ '.Ilw '. : X-/ If A , ,■ r I - 11 - / PAHT IV ✓ RSSUIIJ^ i fa) With c/lindrical stationary cathode and rotary wire srew anode the following data were obtained: 1. r^ilver in Silver nitrate Cathode Weight Before Electrolysis Average loss (Metal) 1' 2 3 4 5 Pnring All. Cold 7.6'559 7,6559 7.6559 7.6560 7.6559 Silver 10.4245 10.5432 10.6620 10.7808 10.8993 * 0.1187 g. Palau 10.6234 10.6233 10.6232 10.6231 10.6230 --0.0001 g. Pt f gauze )16 . 7835 16.7835 16.7835 16.7835 16.7835 Ptf sheet ) 9.4013 ''9.4014 9.4013 9,4012 9.4013 2. Cobalt in Cobalt Sulphate Cathode Weight before Electrolysis Average Loss (Metal) 1 2 3 4 5 Luring All. Gold 7.6559 7.6558 7.6559 7.6561 7.6160 Silver 10.7664 Palau 10.6234 Pt ( gauze )1 6.7836 10.7035 10.6231 16,7833 10.4045 10.6233 16.7336 10.2727 10.6230 16.7835 10.1321 10.6229 16.7836 --0.1561 g.- —0,0002 g.- Pt( sheet) 9.4014 9.4013 9.4014 9.4013 9.4013 3. Cobalt in Cobalt nitrate Cathode Weight before Electrolysis Average Loss (Metal) 1 2 3 4 5 Luring A. 11 Gold 7.6559 7.6559 7.6559 7.6555 7.6557 --0.0002 g.- Silver 10.2263 10.2747 9,3217 8,7941 8.6480 —— 0,4067 g.“ Palau 10,6234 10.6231 10.6233 10 . 6230 10.6229 — — 0,0003 g»— ' Pt (gauze)l6,7835 16.7835 16.7835 16.7835 16.7836 Ptfsheet) 9.4013 9.4013 9.4013 9.4012 9.4014 4* nickel in nickel Sulphate Cathode Weight before Electrolysis (lletal^ 12 3 4 Gold ' 7,6558 7.6559 7.6559 7.6555 Silver 10.8993 10.8816 10.8641 10.8460 Palau 10.6232 10.6233 10,6234 10.6233 Ptfgauze)16.7835 16.7833 16.7835 16.7833 Ptfsheet) 9.4012 9.4013 9.4014 9.4014 Average Loss 5 puring All 7.6557 --0.00C1 g.-- 10.8284 --0.0227 g.-- 10.6229 --0.0001 g.-- 16.7834 --e.OOOl g.-- 9. 4012 ITT' i ( i |i - 12 - PAKT IV •EESUTiTS (a) TTith cylindrioal stationary cath.odes end rotary wire screw anodes the following data were obtained. ilickel in Zichel jiditrate Cathode Weight before Electrolysis fMetal) - 1 2 3 4 Gold 7.6559 7.6558 7.6558 7.6557 Silver 10.8101 10.8051 10.7999 10.7940 Palau 10.6324 10.6235 10.6233 10.6235 Pt f gauze) 10. C835 10.7834 10.7833 1C. 7835 Pt(gheet) 9.4013 . 9.4013 9.4013 9,4013 5 7.6559 10.7888 10.6234 10.7855 9.4014 Average Loss Luring All --0.0078 g.-- — O.OOOl g.-“ 6. Copper in Copper Sulphate Cathode Weight (Metal) 1 Gold 7.7853 Silver 10.8307 Palau 10.6240 Pt(gauze)16.7835 Pt ( sheet) 9.4010 before Electrolysis 2 3 4 7.7850 7.7851 7.6561 10.8420 10.8209 10.7786 10.6234 10.6238 10.6233 16.7835 16.7835 16.7833 9.4011 9.4011 9.4011 7.6559 10.7674 10.6234 16.7838 9.4013 Average Loss Luring All * special --0.0186 g.-- --0.0004 g.-- — — C.90C1 g.~— --0.0001 g.-- 7. Copper in Copper ITitra.te Cathode Weight h'etal) 1 Gold 7.6559 Silver 10.7565 Peleu 10.6233 ptfghuze )16.7835 Pt(gheet) 9.4013 before Electrolysis 2 3 4 7,6558 7.6559 7.6558 10.7454 10.7342 10.7220 10.6232 10.6234 10.6234 16.7835 16.7835 16.7835 9.4014 9.4013 9.4012 5 7.6559 10.71C1 10.6233 16.5835 9.4014 Average Loss Luring All —0.0118 g.-- --0.0001 g.-- 8. Zinc in Zinc Acetate Cathode Weight before Electrolysis (Metal) 1 ' 2 3 4 *Gold 9.9770 9.9770 9.9770 9.9770 Silver 10.6998 10.6994 10.6956 10.6940 Palau 10.6233 10.6254 10.6233 10.6234 *Pt(gauze) 16.9751 16.9750 16.9748 16.9747 *Pt( sheet) 9.5927 9.5927 9.5927 9.5927 9.9770 10.6920 10.6234 16.9745 9.5987 Average Loss Luring All --0.0019 g.-- --0.0001 g.-- Plated witli copper to prevent the formation of platinum black and black gold which are easily lost mechanically. A gold -13- oomplex is formed whicli is soluDle, if the electrode is not pro- tected "by copper. The item marked "Average loss During All" is the average of the four losses as indicated between the five successive weighing’s in each case. The item marked ’•'special, for Gold, under 6. Copperiin Copper Sulphate, is a corrosion loss of gold due only to the use of nitric acid of specific gravity 1.42, con- centrated to that point by allowing it to stand upon a steam bath over night, with the electrodes in it. The loss of weight of the electrode is that occuring both during the electrolysis and the succeeding cleansing; the method for cleansing has been previously mentioned. In the case of the sine electrolysis it was advisable, inasmuch as the \pur pose of the study was the chemical and elec- trolytic action of the reagents, to prevent the purely mechani- cal losses due to the formation of platinum black and black gold, as well as the soluble gold complex solution loss. Eov/ever a fev/ determinations were run on some gold and platinum wire as cathodes, and the results s-re of interest; they follow: 8. Sine in Zinc Acetate Cathode Weight before Electrolysis ^oldfwire) 0.Q341 0.0237 0.0114 Plat. (wire) 0.2746 0.2723 0.2710 Average Loss During All 0.0113 g.- — 0.0018 g. ,1 r , PART Y Discussion There are several points to "be taken into consideration in a survey of the results of this work, including all the physi- cal conditions, as temperature, voltage, amperage, current density time, and the character of the deposit. The latter tv;o points are very closely related and if all apparatus he strictly clean and free from any grease, such as "body oils from the fingers, it is found that the longer the time of deposition the greater v;as the density of the deposit, and its adhesion and cohesion. Of course such a comparison is true as applied to only one metal at a time. Por the purposes of discussion it seems well to mention first the simple electrolytes, and later the more complex. Of the simple type the ones used V/cre silver nitrate, copper sulphate, copper nitrate, and zinc acetate. The complex electrolytes were the solutions of cohalt and nickel salts. The word complex is used in this sense to express the fact that the metallic radical to he deposited exists in the solution in a form in which its primary ionization is as a comlex ion which then ionizes to a lesser extent into the cation to he deposited. The reactions taking place in the electrolysis of silver nitrate, for example, are primarily CuflTOg)^— ^ Cu v SUOg. The copper ion, migrating to the cathode, takes up one electron and is deposited as the element; the ITOg radical while migrating toward the anode reacts with the water to produce free nitric acid with a liberation of molectilsr hydrogen at the anode. There is f - 1 £- also liberation of hydrogen from the cathode, though this is not 8s marked as the evolution of oxygen. It is ^/ell known that this ' procedure requires the presence of a considerable excess of iiitric acid or the solutionnwill become alkaline with an actual odor of ammonia at the end of the electrolysis, in which case the solution resumes a deep nlue color, and the metal deposited is contaminated with oxide. This condition is brought aboiit by the action of the electric current on the ITHOg to produce nascent hydfogen which reduces the nitric acid to ammonium nitrate, perhaps according to an equation resembling 4 F -2 ^ HITOg — sulphate, on the other hand, does not suffer such reduction, and ammonium sulphate will not be present save as traces. In the electrolysis of zinc acetate it is necessary to have a large excess of acetate ion to prevent the solution from becoming contaminated by the pro- ducts of the discharge of the acetate ion. In the electrolyses of the cobalt and nickel complexes the metals are present in the complex cations, as in (liflTEg^n) , which undergoes a secondary ionization and equilibrium, as hi - 4ITH3 hiflE3l4 ; cobalt behaves in this respect similarly to nickel. To prevent the formation of the characteristic nickelous and cobaltic hydroxides it is necesf^'ary to have present a high concentration of OH ions, accomplished by excess ammonium hydroxide. This also lov/ers the concentration of the Co and hi ions but prevents the formation of the oxides and oxide hydrates. It seems from the result obtained that the silver is suscep- tible to loss both in the acid and the alkaline solutions, and there i s little preference for either, thoufch the losses in the 1^ ! ■ f f r V / ’■ i ' I i . I r. vv'^ t t 4 S i !fK y ; I ■, t ■ 'j!< .'! > i • - -4.^ ■ ' ■'• '■' .'• ) r n ' '.r ■ . ‘ jffS '■ ' “f; • ' -16- zinc electrolyses is markedly lov/er than in acid electrolytes. This is a point in favor of the electrodes of this metal, even , ly the oeginning student in electroanalysis. The average error in their use would seem to he in the neighborhood of O.OEOO grams in each electrolysis, and though the acetic acid solution shows the lowest, w'ith an average loss of only a little over C.0019 grams, and the nitric acid next lowest with an average loss of a little over 0.0100 grams per run, the latter would correspond to 1^ of a gram sample, and correspondingly more if the rating be on the percentage of the element determined. The gold cathode lost slightly on first being used in copper sulphate, but after several cleanings and succeeding use, assumed a constant weight, having apparently become passive, by the action of the nitric acid employed in the cleaning. The ”Palau’^ electrode was some- what better than the gold in the matter of corrosion, but for some reason the deposit on a cathode of this metal was of a less dense character, and times it was quite difficult to get a good adherent and coherent deposit. Also this electrode tarnished easily and all the colors of the rainbow would be apparent at the end of an alkaline electrolysis on' that portion of the metal which had not been immersed in the electrolyte. This is the reverse of v/hat would be exp.ected for customisrily the lesser current densities produce the denser deposits, and the ’’Palau" electrode, on account of its larger size, and consequent greater surface, had a. lower current density in its use than the otlers. As would be expected, the platinum electrodes, both sheet and gauze, remained almost constant in weight. The only corrosion - 17 - losses of the platimnn, of consequence, occurred in the c!etermina- tion of zinc, which apparently forms a surface alloy, diffu^jing ' somewhat into the platinum, and yielding a spongy deposit of plat- inum hlack on cleaning the electrode with hydrochloric acid or sulphuric. Such a friable deposit is easily lost, and at best hard to 7/ash clean and dry well. For this reason the zinc elec- trolyses were first rim on small, relatively useless, bits of v/ire of platinum and gold, as gold is simialrlj^ affected. Then the electrodes were copper plated and in such a condition it was found satisfactory to use them, though there was a steady and consistant loss of approximately 0*1 mg at each usage. This use of copper makes the zinc electrolyses a study of the corrosion of copper on those electrodes which v/ere so plated, the gold and platinum, the silver and palau, used without this protecti^on are studies of the effect on these metals direct. ' In the original plan of this investigation we had the idea of investigating tungsten, molybdenum, tantalum, and "Illium” electrodes as well , but this had to be abandoned, due to the difficulty of obtaining material suited to the work. Stationary electrodes ?/ere found to be very imsatisfactory inasmuch as a much greatef dilution was required, and over eight hours time in continuous electrolysis was necessary to get a com- plete deposition of the metal. Within that length of time the Eouroe of current would somewhat, at times was negegible in quantity, and there was a serious loss of water by evaporation of the electrolytes during that length of time, with consequent con- j3Laiitratj.cn -xxi* the.„solutlona*-. — . — . — 9 -18- In one case when the analysis 7/as left, at the end of four hours it was in excellent progression, hut at the end of the next four practically all the deposited copper had been redissolvet" hy the then concentrated nitric acid or remained high and dry on the sides of the dish, mixed with the salts produced hy evaporation. It was found necessary for present purposes to provide for the replenishiment of the water of the solution. Two analyses each were obtained for copper in copper sul- phate only, on the three metals, gold, silver, and platinum, out of some fortliy trials. Their results are tshulated below. Other electrolyses, of cobalt, nickel, and zinc, 7/ere tried out but proved unsuccessful. Cathode f Metal) platinum 5* Copper in Copper Sulphate T7eight before electrolysis Average loss Piiring All Platinum Silver Gold 1 37.9041 43*7818 31.3742 48.6309 37.9040 43.7818 31.1718 48.6310 p --0.2024 g.-r I >1 .• • I - 19 - PAF.T YI In suiaraing up the results of this investigation it must he admitted that there is no logical way of expressing the cor- rosion losses found, in terms of any absolute values v/hich might lead to theoretical conclusions; there is too great a variation for that. The only conclusions that are well grounded ere those of a qualitative estimation of the usefulness of the metals for cathode use in electros-na lysis. It seems that the use of silver is out of the question, for its losses in all kinds of solutions negative the advantage of a low initial cost. Gold appears suitable from the stand- point of corrosion alone, hut because of its lack of rigidity, is easily spoiled mechanically, particularly by the beginner. Palau ware is apparently alright from the corrosion standpoint, and the tarnish it sometimes has is unweighable, but it has the handicap of being unobtainable in the gauze form, and in sheet form takes a deposit that is often nonadherent. Platinum fulfills all the requirements of the electroanalyst • The author of this thesis believes that the best electrode is the one in which the surface exposed to deposition from the electrolyte is of the same metal as that deposited, plated or sol- id; this is of course general, as it is recognized that zinc may well oe plated upon copper, etc. A rigid gold gauze electrode v/ould be the cheapest of the effective electrode materials tested. it’^'' *'*i f ■"' •'■ ■ • * ' ‘ ' .-4> • ^ W' jrl ».'v .-. . IS9-X. ':;« tow ‘ ' -4’ ■;’?*?ir., ‘> •■ ■) ', •';.-©?f ■^•■^' J " ■•’‘tfl ;^;iL- , .,- *■ ■■« *t • »k ■, ' -,-^t 5 V ' w ■ •■’ ■ V/W , y -f ' ^ y:.:...>’to» *' f ' , '■ . ■ .i '■■' ./ ' ’ ' ^:H.v.':' W- k-'.;\'.* , ;■ > * v^.