J. Herovskq Institute of
Polorography Czechoslovak Academy of Sciences Prague 1, Czechoslovakia
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Among various methods of physical and analytical chemistry i t is difficult to find one which would he so closely connected with the life and the work of its originator as polarography. Fift,y years have elapsed since February 10, 1922, when Heyrovskj. recorded t,he first polarographic curve. From that time on, he devot,ed all his activity to further development of the newly found phenomenon. Jaroslav Heyrovskj., horn to the family of a professor of Roman Law, was interest,ed from his very youth in natural hist,ory. His inspiration for this subject was also caught by his younger brother Leopold who later became one of the country's best ent~omologists. However, in his final years in secondary school, Jaroslav's interest moved to mathematics, physics, and chemistry. At last he decided on physical chemistry as the subject of his university study. Since, at. that time, no chair of physical chemistry existed and no course in this field was given at the universities in Prague, he went to London to study at University College. I n 1913 he completed the undergraduate course and began his postgraduate work with Professor F. G . Donnan. His research problem was the determinat,ion of the normal potential of aluminum. His supervisor was Dr. R. E. Slade who had already written on the electrochemistry of aluminum (1). The system aluminum electrode-aluminum ions is complicated both by t,he surface properties of the electrode and by the equilibria among various complexes in the solution. In order to cope with the first part of the problem, Heyrovslcf used, inst,ead of solid metal, an aluminum amalgam which dropped slowly (one drop in several minutes) out of a glass capillary (2). Unfortunately even this electrode showed no iVernst,ian response t,owards aluminum ion concentration. For elucidation of t,he equilibria in the solution Heyrovskj. measured the emf of galvanic cells of t,he type
Heyrovslcfs notebooks (for details, see (9)) give a picture of the basic questions which arose from his experimental nork on the aluminum electrode where hydrogen rTas evolved, aluminum hydroxide showed amphot,eric properties, and aluminum ions associated with other components of the electrolyte. His thoughts were mainly connected wit,h the origin of electrode potential, with the relationship between the electroaffinity (expressed as electrode potential) and the acidic, basic, and amphoteric properties of elements and compounds, wit,h speculations on strong electrolytes, and with hydrogen overvoltage (or hydrogen overcharge, as he called it). Already, in his notebook in 1914, on the last mentioned topic we may find, of
Polarography
course in a rudimentary form, the idea of the "Heyrovskj. mechanism" of the hydrogen evolution reaction. The outbreak of World War I in t,he summer of 1914 prevented Heyrovskf, who was at that time in Prague on vacation, from completing his work in London. He was recruited into the Anstro-Hungarian army xhere, because of his poor health, he served in the Medical Corps. He was sent to several hospitals in Bohemia and Austria where he even found some time for simple laboratory research work (see Fig. 1).
Figure 1. Jororlov Heyrovrk? ar an vncomrnirkned officer in the military hospital in T6bor in 191 5.
I n the autumn of 1918 Heyrovskj. presented his thesis, based on his experiment,alwork in London and on his subsequent thoughts, to theFaculty of Philosophy of Charles University in Prague. One of the contributions of the thesis was a solution of the problem of successive complex format,ion (4) (see Fig. 2) ~11ichcan be compared with the classical work of J. Bjerrum (5). During Heyrovskj.'~PhD oral examination (rigorosum) one of his examiners, Professor B. IiuEera, vho had introduced the dropping elect,rode for electrocapillary measurements (6),drew his attent,ion to discrepancies between the results obtained with his met,hod and with the old method of Lippmann. Heyrovskj. (see Fig. 3), who had just become a university instructor and later a Docent (Assistant Professor) at the Chemical Institute of the University, xas so much attracted by KuEera's problem that he divided his research work between continued investigations of equilibria of aluminum complexes and tedious measurements of the weight of mercury drops which was the experimental basis of KuEera's method. There were two kinds of anomalies in the shape of the electrocanillarv" curves, one annearins in dilute electrolytes (concentration; of thkAdrderof millimolar-for details see ref. (7)) in t,he region of electrocapillary A
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Figure 2. A representation of the concentration of the particles, Ala+/yo/, or determinsd by means of the AIC12+/y~/, AICh+/yl-/ and AICh/yi/ "formation function" (41.
maximum, and another one appearing, as shown by Heyrovski., at the decomposition potential of the electrolyte (see Fig. 4). From the present standpoint the first of these phenomena is connected with the presence of oxygen in the electrolyte, which, in dilute electrolytes, causes streaming along the electrolyteelectrode interface (maximum of the 1st kind) while the other one is due to the sharp increase of the ohmic potential difference in the ceU when the cations of the electrolyte are reduced. I n 1921 Heyrovskj. was already interested solely in the second electrocapillary phenomenon, from which he expected to develop a new method for t,he determination of decomposition potentials. Together with the dropweight method he also measured the droptime of the electrode, which is simpler. In his work he always returned to his old problem, the aluminum electrode. He was so completely absorbed by his work that he stayed in his laboratory even on Sundays. On January 1, 1922, he attempted to measure the current passing through the electrolytic cell during polarization of the dropping electrode. Since his . galvanometer was probably of low sensitivity, he obtained quite hopeless results. At the end of January, 1922, he returned to the determination of the decomposition potential of electrolytes containing aluminum ions hut finaUy decided to investigate solutions of NaCl. On February 9, 1922, he measured electrocapillary curves in 1M NaC1. He obviously had some new research in mind which is shown by his remark about some irregularities on the electrocapillary curve; "At the maximum is something happening but no time to look for this now!" Figure 5. Recorded galwnomater 184
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Figure 3.
Jarorlov Heyrorskj. in 1 9 2 0 Whdo Longhonr, Proguel.
Figure 4. Decomposition patentids determined from electrocapillory meoruremenh with the dropping mercury electrode (8.91.
reodings on Februow 10, 1922.
Figure 6. The first polarographic curve obbinsd b y plotting HeyrovrkG'r 1922. Electrolyte; I M NaCi, open to original data from Februory air. Golvonometer reading (in centimeter4 pertain to the left hand t i l x i . For comparison, the diagram also includes electrocopillary measuremenkfrom February 9, 1922. x = weight of 30 drops in grams, o = drop-time of 50 drops (seconds). Hoyr&sk+'r remark3 put down during the moorvrement are also reproduced.
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On Fehurary 10, 1922, he connected a mirror galvanometer (lent by the Physics Professor, F. ZAviSka) in the measuring circuit. At an external voltage of 0.1 V a small deflection of the galvanometer was observed, and the light spot oscillation started to correspond to the drop periods. Two pages of Heyrovslcj.'~notebook (he wrote his remarks mainly in English), with the first measured values. are re~roducedin Fieure 5. When the e~~erimental'values were plotted in a diagram (Fig. 6) one could see that Heyr0vsk.J.had measured, in fact, the reduction wave of oxygen to hydrogen peroxide and of hydrogen peroxide to water. This he did not notice, and was not lookine for it in his exueriment. since he was interested in the potential range 1.9-2.0 V where the deposition potential of Na+ was situated. I n the next few days and following weeks he determined the influence of the droptime on the decomposition potential and the potential of the collected drops, which corresponded t o a dilute amalgam, then tried a number of various electrolytes etc. Soon afterwards he wrote the first polarographic (not so called at that time) paper "Electrolysis with the Mercury Dropping Electrode" (8, 9). Here he stated the principle of polarographic electrolysis which is still valid
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In using the dropping mercury as cathode, it has heen observed that in neutral or alkaline solutions hydrogen is not evolved even at high polmisations. This arrangement seemed thus convenient to study the cathodic deposition of the most "posit,ive" metals, which are otherwise attacked by water. Besides the high overvoltage the dropping mercury electrode possesses other advantages: it yields in the solution always s. fresh and pure mercury surface, avoiding thus any "concentration polarization"; further the drops when falling on the bottom mercury used as anode also produce stirring there. The bottom layer of resting mercury when in a. solution of halide or hydroxide keeps up the well-defined potential of the respective standard electrode, and thus can he relied upon as an exact reference electrode.
Fieure 7. Decomposition potentials determined from polarization curves with the dropping mercury electrode (8, 91.
When a cathode of very small dimensions is polarized, the large reference electrode being used as anode, the decomposition E. M. F. must be equal to the differencebetween the potential of the electrode used as anode and the potential at which decomposition takes place at the cathode. Let us denote the latter as the "deposition potential" of the cation in mercury. To show that this deposition potential is independent of the anion, solutions of chlorides and hydroxides of the same metal in various dilutions were electrolysed, and from the results the deposition potentials referred to the normal calomel electrode were calculated.
The resulting curves measured in the presence and in the absence of oxygen are shown in Figure 7. Heyrovskj. ascribed the waves of Oz and H2O2,recorded in a strongly simplified way, to the oxidation of the mercury surface by oxygen. The paper closes with a very clear theoretical treatment of the exponential shape of the I-E curve of metal deposition with amalgam formation. It is, however, impossible to find the exact day when Heyrovskj. noticed a limiting current and determined its properties. This happened probably some time in the spring of 1923 in his joint work wish Miss H. KadlcovA on polarography of lead. A full review of all these results was presented by Heyrovskj. at the General Discussion of the Faraday Society on "Electrode Reactions and Equilibria" (10,11). This meeting was the first step in the journey of Heyrovskj.'~method to its present fame. The Author is much indebted to Mrs. M. Heyrovski and to Dr. 11. Herovskj. who put at his disposal original notebooks of Professor Heyrovslrj. and supplied him with extensive additional information. Literature Cited (1) (2) (3) (4) (5) (0)
(7) (8) (9) (10) (11)
SLADE, R. E., S. Elcktrochcm., 17,201 (1911). HEYROVBRL. J.. J . Chcm. Sor.. 97, 27 (1920). K o n r ~ nJ.. , Chem. Lidv. 64, 1236 (19701. Er;movsa+,J.. J . Cham. Soc., 97, 11 (1920). Blennnr, J.. "Metal kmine Formation i n A~ueousSolutions," D. Has88 and Son, Copenhagen. 1941. KUEEM, G., Ann. Phvs. (Drude). 11, 529. 098 (1903). H e ~ n o v r ~ iJ. - , *ND Kim*, J., "Principles of Polarogra,~ h y . " Aoademic Press New York. 1965, p. 23. H ~ u n o v s n i -J.. , Chem. Lnsty, 16,250 (19221. H ~ m o v s a i .J.. . Phil. Mas., 45,303 (1923). Hmnovsxt, J.. Tions. Foradoy Sac.. 19,692 11924). Hmrnovsxi., J., Trans. Foroday Soe., 19,785 (1924).
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