A STUDY OF THE FACTORS AFFECT- ING THE ELECTRODE POTENTIAL OF ZINC BY ARTHUR ROWAN MURPHY THESIS FOR THE DEGREE OF BACHELOR OF SCIENCE IN CHEMICAL ENGINEERING COLLEGE OF LIBERAL ARTS AND SCIENCES UNIVERSITY OF ILLINOIS 1922 I 922 M95 UNIVERSITY OF ILLINOIS THIS IS TO CERTIFY THAT THE THESIS PREPARED UNDER MY SUPERVISION BY _ _ _ Jtowan Uurph^ _ EN titled A_ _Stud^ _ of _ t he _ Pac t or s _A f f _e_c t ing _ t_h e_ El e c t r ode Potential of Zinc, IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS FOR THE DEGREE OF in Chemical Engineering, Instructor in Charge Approved iLUY-' ACTING HEAD OF DEPARTMENT OF -HHEMXSTIIY-: 500208 Digitized by the Internet Archive in 2015 https://archive.org/details/studyoffactorsafOOmurp Iclmowlodgment - Introduction Theoretical Historical experimental Conclusion and Surarnary- paae - 1 . - 2 . 4 - 14 . 15 - 23 . Bibliography- ■24 . - ACMOVh^GdThT The author v/ishes to take this opioortunity in expressing his sincere appreciation and thanks to Doctor Gerhard dietrichson, under whose direction this investigation v/as carried out, and for '..hose co-operation and assistance he is indebted. - 2 - Intro Auction Inny methods have "been tried in an effort to determine the elec- tro de potentials of the more simple metals such as zinc silver, copper, and cadmium. 'iiile most of the investigations carrie: 1 out up to this time have "been successful in the determination of the potentials of the metals in contact with concentrated solutions of their ions, it has been near- ly impossible to find a method which will give results in the more di- lute solutions. The fundamental importance of electrode potentials in explainin' electro-chemical reactions led to the experimentation ana results which are given in this article. due to the limited amount of time and the many difficulties en- countered, the electrode potential of zinc v/as the only one considered in this worh. -o- Theoretical The eloctrod potential represents the work done in carrying unit quantity of electricity between ^electrode and electrolyte. Hie normal electrode potential lias been defined as the electromotive force of a reversible electrode of the pure element against a solution in which the ion of the- element is (hypothetical) molal. Hie electrode -potential of a metal in contact with a solution containing ions of that metal, is dependent on the concentration of the ions in solution. If the ion is positive, the potential difference becomes more positive with increase in cone ntration. If the ion is negative, then the potential becomes more negative or less positive with increase in concentration. By say- ing /the potential becomes more positive or mors negative is meant that they are positive or negative in relation to the hydrogen electrode which is considered as zero, when the electrode values are given in re- f'rence to the hydrogen scale. All values given in this article are con- sidered with reference to hydrogen as zero, as above stated. ■Historical Many investigators have worked with zinc potentials, "but most of those have determined the potential of the metal in contact with a sat- urated solution of the zinc salt, or in highly concentrated solutions. Che determinations of the potential in dilute solutions s eras to have given rather indefinite and varied results. In spite of this some very interesting work lias been done along this line, an' altho no positive solution has been derived at, the investigators have thrown light on the problem an! have indicated the way to further investigation. A brief review of the work already published on this topic will bo given. It may be said at this time that the results given in this article were more or less obtains:' by a method of experimentation ob- tained by a collaboration of the conclusions of former investigators and supplemented only by original ideas which would furnish a more speedy method of determination, requiring only a limited amount of skill and in this way sacrificing the minute accuracy of the former investigat- ors . One of the first investigations was that of Richards an' Lewis (l). Chev studied electrodes of zinc amalgams of different concentrations and solid zinc electrodes oppose' to zinc amalgams. Measurements were made at such temperatures that the amalgams were wholly liquid, for their partial solidification is an insiduous cause of error capable of prodticing serious results. It was noticed by Meyer that the e.m.f. of a cell of this kind in- creases rapidly on standing. Altho no explanation can he given of this phenomena, oneraay prevent by using as an electrolyte a solution which has remaine' standing in contact with the amalgam for several weeks be- fore being used. Mhe constancy thus reached assures much greater accur- -5- acy than cor.l otherwise he obtained. Theoretically the value of the anion of the electrolyte or the concentration of the cation should be without effect upon the results of the values obtained for cells of the type used in this investigation. This prediction was verified by- experiment. The cells with electrodes of zinc amalgams were less con- stant than those with cadmium. A tabulation of these results is given below. Zinc Amalgams. Cl C2 Cl t. -3. obs. 1. calc. E C2 m X 1. 1 I o 9 30 .02890 .02860 .0000954 2. 1_ J 1 3 27 9 30 .02920 .02860 .0000964 3 • 1 1 3 9. rr O 30 .01425 .01430 .0000470 4. 1 1 9 27 rr o 30 .01515 .01430 .0000500 The rnea .suremont of ' the contact potential of solid electrodes always been subject to considerable uncertainty, due to the accidc of crystallization, condition of surface polarization, an: other un- known causes. It seemed possible that by sufficiently increasing the extent and diversity of the surface an electrode might be obtained whose surface and potential would bo the mean of a large number of diff- erent values and therefore constant. An electrode of this type c ns is ting of a quantity of the finely ivided metal perhaps a cm. in depth, pa ch- ed loosely around a seale:’ in platinum wire seemed likely to satisfy the desired conditions, and experiments were male with electrodes of this sort and yielded remar dbly satisfactory results. The difference in po- 1 ntial between the soli metal ana the amalgam should be emphasized. -7- It is often stat i that the potential of the saturated amalgam may ho considered the potential of the true metal. In th case of zinc this is true within a few thousandths of a millivolt. The results obtained by these men are given here nd really show a remarkable- agreement between ■-he potential of the zinc amalgam and that of the zinc in thesolii form Z inc ver s e s malgam . cell t H obs • E cale. 1 30.0 .01175 .01160 .01165 2 0.0 .00570 .00560 .00565 rr O 30.0 .01170 .01160 .01165 4 36.2 .01285 .01289 5 34.5 .01270 .01260 .01255 6 32.6 .01230 .01215 .01217 7 30.0 .01170 .01160 .01165 8 28.0 .01125 .01120 .01125 9 26 . 6 .01095 .01080 .01097 10 26.7 • .01100 .01089 .01099 11 23. 8 .01045 .01030 .01041 13 15.7 .00885 .00870 .00679 14 16.0 .00890 .00675 .00885 Frank J. He 11 encamp (2) in working on the application of the Gibb s -He c|rriho 1 1 z to concentration cells usee 1 zinc amalgams in contact with zinc sulphate solutions, end arrived at some very interesting re- sults. As with the fault of many former investigators, his work with mere or less concentrated solutions, the most ilute electrolyte use' being one mol of zinc sulphate with four hundred moles of water which is approximately .14] . He found that amalgam electro es are best adapted for work on elec- paring his zinc chloride solutions will he given here. The zinc chloride solutions were prepare ’ 0 / i luting a stool: solu- tion of zinc chloride. This stool: solution v/as prepared as follows: Pure hydrogen chloride was proper ed by drop ing pure cone ntrate' sulphuric acid slowly into pure concentrated hydrochloric acid. The gas was absorb- ed in conductivity water until the concentration was about 0,5 i. -in ex- cess of spongy zinc, carefully washed, was then added to this acid solu- tion and the mixture warmed gently until nonfur ther zinc would dissolve. Zeis solution re den 1 litmus slowly. The solution was then filtered to remove the excess zinc and the filtrate diluted to about 0.15 II nd employe as a stool: solution. As has alrea y been stated finely divided zinc was used instead of zinc amalgam because the amalgam gave unsteady values of electromotive force. Between two samples of the amalgam the electromotive force var- ied in an erratic meaner rising and falling rapidly. The finely divided zinc gave a steady value, but left something to be desired in reproduc- ibility in the dilute solutions. For this reason the measurements were not carried out in zinc chloride solutions more dilu than 0.0003 1., a nd in concentrations below 0.C01 Id the deviation from the mean is 0.002 volts. In the table given below are represented the observed e.m.f.s of the cell Zn ; ZnCl (c); ArCl A . In the second table the results given by H. Jahn are given to supple- ment those given in table 2. Jahn used an amalgamated zinc rod instead of purr zinc. 'Since as pointed out b^/ Pichards and Lewis (l), the diff- erence in potential between pure zinc and its saturated amalgam is slight (only a few millivolts ) the comparison is a fair one to make. He found that the normal electrode potential of zinc 7, as 0.753, f I - 10 - Table 1. c.u.f. of coll Jn : GnCl^c); J1 c. Sn d l moles per 1000 g. water. 0.01021 0.006022 0.003112 0.001453 0.001253 0.000772 0.000649 0.0003995 0.0003478 (observe! To Its] 1.1558 1.1742 1.1953 1.2219 1.2289 1.2475 1.2497 1.2699 1.2701 Table 2. 0.566 1.0306 1.112 1.0171 2.220 0.9740 The next work done on the zinc electrode was that by ill ian G. Iloore. His work was entirely confined to the use of zinc amalgams . In a study of the literature ho found that all previous investigat- ors had confined their attention euther to dilute zinc amalgams of van— in g composition and constant concentration of electrolyte, or to zinc - amalgams or to amalgamated zinc, with salt concentrations not less than 0.5 IT. I oreover in particularly all instances it was found necessary to take some sort of precautionto prcventaccess of atmospheric oxygen to the electrolyte and to the electrode. Moore found in his work which dealt with the electrode potential of amalgamated zinc rods in a solution of zinc sulphate varying in concentra8- tion from 0.5 IT down to 0.002 IT, after considerable experimentation, that zinc electrod' s reproducible at room temperature to within one millivolt could bo secure- by using well amalgamated zinc rods, and by bubbling hy- drogen thru the zinc half-cell during the mearsurements • As site . by him, I'ellencamp has shown that with an amalgam contain- - 11 - ing about 1$ sine, the temperature coeffient of the electrode potential of sine is very small and his onw work shows that changes of several de- grees in the temperature have only a slight effect. The results obtained by him are tabulated below. C f t. I 31 y a 1 Con. IT. mean obs. S. E calc. CX 0.5 0.5 -0.784 -.0780 30 0.1 -0.800 -.800 45 0.01 —0.823 -.824 70 0.002 -0.840 -.850 85 As the results of his work he arrived at the following conclusions and summary. & x rim e* f&rs 1. Obsrevations of previous^ are confirmed in that it is necessary to exclude oxygon as completely as possible in setting up sine electrodes. 2. Electrodes reproducible to within one millivolt can be securdd by making the dilute solutions with water recently boiled and cooled in hydro- gen, the dilution taking place in an atmosphere of hydrogen with the meas- urements being made while the hydrogen is bubbling thru. the electrode vess- el. 3. Using the precautions Just described the electrode potential of sine in 0.5, 0,1, 0.01, 0.002 II concentrations of zinc sulphate have been measured at room temperatures. Calculated values base" on the electrolyt- ic dissociation of sine salt and these measurements are in good agreement with each other. In a recently published article by Theodore Richards and Theodore dunham Jr., they have shown the effect of changing hydrogen-ion concen- tration on the potential of the zinc electrode. '.Then a metal of weak basic character (such as gallium) is studied with regard to its single electrode potential, the salt solution in which the metal is immersed must be acidified to prevent hydrolysis. According- - 12 - ly their paper recounts a brief s tudyno f the effect of adding acid to the salt solution ar< a typical reproducible electrode, in order to demon- strate eirp or imon tally the sign and magnitude of the potential difference thus caused. Keasur orients of the potential of sine in acid solutions of sine sul- phate measured against the calomel electrode (thru a sodium sulphate i&ge] and also iirectly against sine el ctrode containing p 0+ solution shorn d marked rise in potential as the acid concentration ms i .creased. Che magnitude of this rise in potential indicate that it must he due to the liquid junction potential owing to tl the hydro- gen ion. Hqual concentrations of t" sulphate ion in the form of alhali sul- phate add d to the sine sulphate solution gave smallei elev tion itential which were in the order of the transport numbers of the cations cone rned. If it is assumed that the change in junction potential pro- duced byt sodium sulphate is small, one may infer that about 2/3 of the change produced by the sulphuric acid is due to solution junction potential and the other third to a real increase in the single electrode potential of sine, due to , presumably, t' e depression of the electrolytic disso- ciation of the sine sulphate. Cho results as obtaine by these mon arc given. t.ab' 1 o 3. In summing up the worh of the for mentioned, investigators, we arrive at the following conclusions that have a direct baring on the problem un- cons id .ration. 1. d .: .d. of the typo of coll vn dor Consideration increases rap- idly on standing, do is may be prevented by using as an electrolyte a solu- -13- ticn which has remained standing in contact with the amalgam for sever- al weeks "before using. 2. In the c;' sc of sine the po + ontial or" the saturated smalg. .mis * 1 th- in a for millivolts of the potential of the pure metal. 3. .inr.lga.rn electrodes arc host adopted for work on electro do potentials of sine, fine with pure metals it is very difficult to prevent oxidation or to exclude occluded gases variable and unsatisfactory results are ob- tained. 4* Upon diluting zinc chloride solutions hydrolysis takes place caus- ing a change in concentration. 5. fine sulphate solutions giro more consist ts than those of zinc chloride. 6. for work with dilute solutions it was impossible to obtain repro- dticibl results”'! th a flowing el' ctrolytc . 7. Electrodes reproducible to with in one mi?.livol J ' can be secur making the dilute solutions with water recently boiled an 7 cooled in hy- drogen, the dilution taking place in an atmosphere of hydrogen and the meas- urements being made while hydogen is bubbling thru the electrode vessel. 8. Changes of several degrees in temperature have only a slight effect. 9. If the electrolyte is acidified the potential Is increased. The last statement seems to be in direct opposition to the results that were obtained by Korsch, for as was stated ‘ efore all his results were obtained 7 " using a zinc chloride solution that was "istinctly a oil la aracter. SPhis would tend to make his results higher than the to ore t- ical values. It was due to this acid condition that he was able to pre- vent hydrolysis which otherwise would have led him into many difficulties. It was wit! t3 • conclusions that the experimentation on this rob- lom was carried out -14- r n2-le 5. 2 k 0 ,. Total potential / IT. ornel electro's. 0.0 1.0777 0.1 1.0328 0.5 1.0971 1.0 1.1066 2.0 1.1175 4.0 1.1277 0.0 again 1.0771 T ange of Potential. 1 . i + ■ » ' z + "hr i&ge "bridge nv. irrv. 0.0 0.0 5.1 6.0 19.4 21.6 28.9 52.6 59.8 45.3 50.0 57.5 ( -0.6 ) 0.0 -15- Experimental tthrup Student potentiometer was us . ' in ml i tl s«m. f • To terminations. A "oston coll v/as used as a standard and a n/lO c-lonel cell as tile reference electrode. A 5H KC1 solution was us' es a "buffer to eliminate liquid junction potentials. The first worli was lone using an electrolytic zinc amalgam as an elec- trode. Very inconsistent results were obtained, foe cause of which was later found to be partially due to the fact that the amalgams were only ■tially saturated. In these ie terminations zinc sulphate solutions o: I , Il/lO, I./lOO, ll/lOOO concentrations v;ero used. The results obtained in the 1- andld/lO concentrations were found to be fairly constant but wore low due to the partial saturation of the zinc amalgam. Hie results obtained in the Id/ 100 and I.l/l000 solutions were ridicuously inerts is tent, at times, the otential going in the wrong direction upon diluting the electrolyte. It was thought advisable to try using zinc chloride instead of zinc sulphate as the contact solution. All attempts to dissolve chemically • pure zinc chloride in water were unsucessful due to the high degree of hydrolysis. Hie method used by Borsch was then resorted to, that is, dissolving pure zinc in a solution of hydrochloric acid of known 0 f ig^tjL Platinum was used as a catalylizer in aiding in the solution of the zinc, and the solution heated to aid in the reaction. After all reaction bet": n the zinc and hydrochloric acid load coasod the solution was tested with lit- mus and found to be distinctly j^pi'.. Hie excess zinc was then filtered off and this solution used as a stoch solution, op on diluting this solution to IT/10 hydrolysis to oh place, this necessitated re filtering the Il/lO so- lution, consequently a lowering of the concentration. As the results de- sired were only to be approximate this fact was not tahen into consider- ation - 16 - r'our mechanic ly made amalgams were used and were 1, 2, S,an& 10fb zinc respectively. The main intention in using those certain concentrations was to determine the point at which the amalgans would he come saturated and whether or not that after reaching saturation the potential of the amalgams woul remain constant with varying amounts of zinc, tfteso amonts h- ing a- hove the saturation point. The amalgams were made hy shaking chemically pure zinc in contact with mercury which load been purified with nitric acid and lisstilled. The vesults obtained with the amalgams in contact with the Id and Id/ 1C solutions of zincchloride showed a narked degree of consistency. They also showed that the electrode potential of the amalgam increases direct- ly it' the concentration of the zinc in the amalgam form up to the point of saturation. After the point of saturation has be n reached the poten- tial of the amalgam remains constant with an increasing concentration of the zinc. The results obtained for these two concentrations of el ctro- lyte are given below. Zn (amalgam)/ II ZtTSO/ 3 i I KCl/ ca! Lomel. fo zinc in amal. 1. 2. •- • • o l — i e.m.f. e.m.f. e.m.f. e.m.f. -1.0925 -1.0990 -1.0990 -1.0907 1.0927 1.0989 1.0985 1.0980 1.0925 1.0990 1.0988 1.0985 1.00925 1.0992 1.0987 1.0985 1.0925 1.0992 1.0987 1.0985 1.0925 1.0980 1.0987 1.0S87 1.0927 1.0979 1.0980 1.0986 1.0927 1.0977 1.0987 1.0985 1.0950 1.0977 1.0986 1.0985 1.0929 1.0975 1.090 5 1.0985 ave. e.m.f. -1.0920 -1.0984 -1.0987 -1.0980 E. P. -0.7560 -0.7024 -0.7627 -0.7020 ‘ • • ■ i -17- 2ii amalgam/ .11 ,j nine in amalgam 1. e.m.f . -1.1275 -1.1272 1.1271 1.1278 1 . 1270 1.1270 1.1268 1.1266 1.1265 1 . 1262 - ave. e.m.f. -1.1270 E. P. -.7910 * TTC1/ calomel. 2. 5. 10. e.m.f. e.m.f. o .m.f . -1.1354 -1.1352 -1.1350 -1.1555 -1.1350 -1.1352 1.1351 1.1350 1.1350 1 . 1547 1.1350 1.1351 1.1345 1.1348 1.1353 1.1350 1.1356 1.1352 1.1347 1.1352 1 . 1352 1.1344 1 . 1352 1.1350 1.1345 1.1354 1.1352 1.1545 1.1350 1.1352 -1.1548 -1.1351 -1.1351 -.7988 -.7991 -.7991 In plotting these results against the concentrations, it is shown that a zinc amalgam of between 2 end Z% zinc is saturate; . It is also shown that after reaching the point of saturation the electrode potential of the. metal remains constant. Erie results shown here are by no meahs due to the inexactness of the concentrations of the solutions. But the relative values of the potential in I.' and I'/lQ concentrations have very near the teoretical relation and show that in the more concentrated solut'ons of zinc chloride the poten- tial of zinc can be determined with a fair degree of accuracy, and with a limited number of precautions. These four amalgams were trie in the zinc chloride solutions of h/lOO and Id/lOOO concentrations but it was impossible to obtain any con- stant or reproducible results. Ehe met od of using a flowing electrolyte was resorted to but seemed to have no effect on giving more constant val- ues than those obtained with a stationary electrolyte. In making th se de term:' nations an electrode vessel of the type shown in the illustration was used. In using a flowing electrolyte si la 1 sep rat ' i si d funnel nearly touching the surface of the amalgam. The electrolyte was -18- run into th n* ns, tirnos keeping the Surface of the amalgam in contact with fresh electrolyte. Che amalgam use was at all times kept covered with a co c ntrated solution of the zinc salt which kept it free from oxidation. Just "before being used it was thoroughly washed with disstilled water, and at all times kept out of contact with the air. In inserting the amalgam into the electron v vessel it was x>ipetted out of its container with a one c.c. pipette and run into the vessel already containing the electrolyte. Chose pirec- utions wore taken to prevent undue oxidation of the electrolyte and the amalgam • by the air. Since it was impossible to obtain results with saturated amalgam in dilute solutions, the 1'Moly divided metal was tried. This metal was ob- tained by electrolytic deposition from its salt solution and was obtained in its spongy form. As in the case of tho saturated amrlgam goo results were obtained in the M, M/lO zinc chloride solutions but in the more di- lute solutions the same difficulties were encountered as in the previous experiments. It 7/as thought at this time advisable to check up the electrolytic zinc with the concentrated amalgam. As the results given in table 4. show, the potential of the spGngy metal an ’ the saturated amalgam agree within 0.4 millivolt this is close enough for the purpose for which this invest- igation vas carried out. It shpws that it is perfectly legitimate to use the saturated amalgam in place of the pure metal. In fact, it is highly advisable for it is much, easier to get a good contact and the readings are much more constant with the amalgam. It is easier to handle, and the surface strains are eliminated. -19- "'loctrolytic nine zinc amalgam J ' ~ X: electrolytic amalgam. 3c.tu.rat T amalgam e.m.f . -1.1153 1.1155 1.1158 1.1155 1.1159 1.1160 1.1157 1.1158 1.1160 1.115 e.m. f. -1.1156 1.1154 1.1155 1.1153 1.1153 1.1153 1.1154 1.1152 1.1153 1.1155 Ave -1.1157 -1.1153 Since it was impossible to obtain reproducible results of the potential of saturated amalgams in contact with th dilute zinc chloride solutions it ms thought that this may have been due to the extensive hydrolysis of zinc chloride in solution. It was thought advisable to make one more attempt with zinc sulphate. As before very goo’ results w- r r obtained in the I and Y / 10 concentrations but beyond this dilution the results v/ore not constant, altho, much improvement could be sex over those ob- tained in the zinc chlori’e solutions. In taking readings in the dilute solutions much difficulty was en- countered due to th' ir low c nductivity. A moans of remedying this trouble v/as tried an showed that the method had many possibilities. Since the t trouble under consideration v/as due to the low conductivity of the solu- tions, the means of elininat'ng this consisted in addins some inert salt to the solution which would incr- use the conductivity and not effect the ionization of the zinc sulphate. .1 IT was aided to the IT zinc sulphate to increase its conductivity. Four cells were tried containing- 0.0, 5.0, 10.0, an" 15.0 c.c. of .1 II KOI per 50 c.c. M zinc sulphate respective- ly. Checks on these colls wore run and pur lisstill i water was used - 20 - in place of the TCI J -n le to mine 7/hether or not the KOI had any effect on the potential. The results obtained are shown below. .1 r TC\ in 5C c.c. !* TnSO*/ lei. . o . o a o rH a r 1 • 5 c . C'. 10 c. c. 15 c.c. e.m.f . e.r.f. e.m.f. e.m.f, -1.1184 n •> J. £.■ -1.1216 -1.1240 1.1180 1.1200 1.1215 1.1238 1.1183 1.1205 1.1221 1.1235 Ave. -1.1182 -1.1204 -1.1217 -1.1238 Diff. in m.m. 2.2 1.3 2.1 Duplicate cell using 7/a ter ins tea ■ of . 1 IT KGJ. 1.1194 1.1215 1.1235 1.1194 1.1214 1.1235 1.1194 1.1214 1.1231 Ave. -1.1194 -1.1215 -1.1234 Diff. in m.m. 2.1 1.9 These results are hardly general enough to draw any conclusions from, hut at least show that this proceedure has possibilities. They al- so do not show us the effects in dilut solutions. The determination of these effects would constitute a problem in itself. Due the limit: a- mount of time no mere work was 'one along this line except to make an attempt at using the KOI in the two dilute concentrations. It was found th t more accurate readings could be obtained but as before the ree finds varied. In the first part of this article the r - suits obtained by Ido ore and the conclusions arrived at by him were discussed. The method used by him next tried. This method seems to have great possibilities and with the modifications given gave very satisfactory results. Tiie results in the dilute solutions wcr~ obtained by using a cell which hertofore load been used as a hydrogen electrode and seems to be the mosi satisfactory tj’pe that could be used with this method. The solutions v/ere placed in this cell and thoroughly saturated with, hydrogen before inserting the am&lgam. The flow of hydrogen thro th: electrolyte 7/as con- - 21 - tinued during: the entire proc ss of inserting the amalgam and while the measurements were b ing made. One of the most striking effects of tais method is that the surface of the amalgam remains bright four hours, while in the other methods tried the surface of the amalgam became coat- ee with a grayish white precipitate after a very short time. From this effect it seems that the large deviation of results obtained in the dilu te solutions, without being at all times saturated with hyt rogen, 7/as due to the hydrolysis of the electrolyte or the oxidation of the surface of the amalgam by- the dilute electrolyte. file results shown here for the potentials in the M an' Y.J 10 solutions were obtained without the use o f hydrogen since those results could be obtained without any difficulty an with an exactness which was sufficient for this purpose. ©lose given for the M/lOOand I'/lOOO solutions were obtained by bubb- ling hydrogen thru the electrolyte in the manner before described. Zn amalgam / M Zn 30 f / 3N KOI / cal oi 1. time 2. time 3. time -1.1280 1/45 -1.1277 1/45 -1.1269 1/51 1.1280 1/54 1.1272 1/55 1.1272 1/55 1.1276 1/57 1.1272 1/58 1.1271 1/59 1.1275 2/05 1.1265 2/08 1.1272 2/10 1.1270 2/11 1.1266 2/12 1.1272 E/16 1.1270 2/17 1.1264 2/18 1.1269 2/20 -1.1275 -1.1270 1.1271 Zn aralgam /O.llT \ 5nS0 # / 3 I KOI / calomel -1.1505 9/45 -1.1497 9/56 -1.1494 9/54 1.1507 10/00 1.1499 10/49 1.1497 10/52 -1.1506 -1.1498 -1.1496 Zn amalgam / o.Ol U Zn 30 * / 3 IT KOI I calomel -1.1679 9/13 -1.1679 6/07 -1.1678 5/57 -1.1679 9/25 -1.1682 9/21 -1.1680 9/l6 1.1678 1/31 1.1679 1 /28 1.1674 l/34 Ave. -1.1679 -1.1680 -1.1677 - 22 - Zn amalgam/ 0.001 r ZnoO*. / 3 TT EU1 / calomel. 1. time 2. time -1.1923 l/46 -1.1919 1/45 1.1924 1/59 1.1922 1/58 1.1927 2/14 1.1927 2/12 1.1931 3/45 1.1935 3/43 1.1930 5/16 1.1933 4/26 1.1930 5/41 1.1939 5/40 Ave. -1.1928 -1.1930 Average Results. con. Difference electrolyte e.n.f. 2. potential m.m. M. -1.1272 -0.7912 0.1 M. -1.1500 -0.8 140 23 0.01 M. -1.1679 -0.8320 18 0.001 11. -1.1929 -0.8570 25 If the results obtained are plotted v/ith those obtained by Iloore ( as in the grapfe ), it is seen that altho the results are not absolute- ly the same, due to only a necessary amount of precaution in the experi- mental work, they have nearly the same relation. Ibis prooves the unlim- ited possibilities of this method of determination and opens a large field of investigation. -L3- Conclusior. and Summary. 1 . concentration du to the high degree of hydrolysis. 2. The electrode potential of zinc amalgam increas s directly wit' tl tr concentration of the zinc in the amalgam form up to the point of sat- uration. After the point of saturation hcs "been reached the potential of the araclgam remains constant with an increasing concentration of the zinc. 5. A saturated zinc amalgam contains between £ and 3 fo zinc. A. In the more concentrated solutions of zinc chloride the potential of zinc can "be det rain d with a fc ir degree of accuracy and with a lim- ited n' mber of precautions. 5* It was impossible to obtain results with the saturated amalgams in dilute solutions even when resorting to r. flowing electrolyte. 6. The potential of the spongy metal and the saturated amalgam a- gree within 0.4 millivolt. 7. The addition of IIC1 to the electrolyte to increase the conductiv- ity Was shown to have no effect on the potential in the concentrated so- lutions. Limited time prevented its trial in the dilute solutions. 8. Very good results werr obtained in all dilutions by using a zinc Sulphate solution saturated with hydrogen and bubbling a continuous stream of hydrogen thru the electrolyte while the reelings arr being tahen • I ; -24- Bibliography. 1. Hi char els and Lewis. Proc. Amer. Acad. , 34-, 98 (1898) 2. lie 11 encamp, Phys. Lev., 29, 329 (1909) 3. lloore, J. A. C. S., 43, 81 (1921) 4. Theodore 7. Richards and Theodore Lunham, Jr., J. A. 0. S., 44, 678(1922) 5. Horsch, J. A. G. S., 41, 1787 (1$19) '