Development of the Glass Electrode - ACS Symposium Series (ACS

Chapter 19

Development of the Glass Electrode

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 4, 2016 | http://pubs.acs.org Publication Date: January 1, 1989 | doi: 10.1021/bk-1989-0390.ch019

Carl E. Moore 1 , Bruno Jaselskis1, and Alfred von Smolinski2 1Department of Chemistry, Loyola University of Chicago, Chicago, IL 60626 2Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, IL 60680 The development of the glass electrode as a practical working device has been an evolutionary process. The paper describes the electrode's developmental stages which involve experiments on the conductivity of glass, the use of glass as an electrolyte in voltaic cells, the discovery of the response of glass to the hydrogen ion, the improvements in electrode response through control of glass composition and fabrication, and the development of devices for measuring voltages in circuits containing high resistance components. The glass electrode is the premier indicating electrode in the field of analytical chemistry when breadth of use and the quality of selectivity are the only considerations. Its practical importance puts it high on the list of historical topics which need to be included in the teaching of the culture of chemistry, but it must be noted that the history of the glass electrode is of interest from several points of view other than that of the immense importance of the electrode itself. Reflected in the records that embody the development of the glass electrode-in a way rarely equaled—are the tenacious spirit of scientific inquiry and the important part frequently played by intersecting technologies in technological developments. The history of this electrode emphasizes the critical roles occasionally played by unsung heroes and also, by means of its very rich literature, describes in great detail the development of our most widely used indicating electrode system. Even a rudimentary knowledge of State of the Art electronics of our time-the 1980s-makes it abundantly clear that most of the difficulties encountered in the early developmental work on the glass electrode are directly traceable to the fact that 0097-6156/89/0390-0272$06.00/0 © 1989 American Chemical Society

Stock and Orna; Electrochemistry, Past and Present ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


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workers of that period lacked a means for permitting accurate and reproducible measurements of the voltages of cells in which glass—i.e., a very high resistance-was a circuit element. The problem of measuring potentials in circuits containing very high resistances was not resolved in a practical way until there was an intersection of the electrochemical and communications technologies . This technological crossover came about via the utilization by the electrochemists of the development of the Audion, the first triode, by Lee de Forest in 1906. A major thrust of the research at the time of de Forest was to produce devices that would improve the strength of the wireless-telegraphic signal. Early Work The study of electrical properties of materials started systematically with the development of the Electric Machine and the Leyden Jar. These developments allowed the researcher to produce and store the electrical charge on command and by this means to become able to exert a significant amount of control over the electrical experiment. In 17 61 Benjamin Franklin (1) reported that some of the work of Lord Charles Cavendish, the father of the famous Henry Cavendish, demonstrated that glass heated to 400°F became a conductor of electricity. About a century later (1857) remarks by H. Buff (2.) make it seem likely that the electrical conductivity of hot glasses was a well-known phenomenon. Buff pointed out that everyone knows that different kinds of glasses differ significantly in insulating ability, that potash glasses are usually the best insulators, and that sodium glasses are less effective insulators. He mentions a very conductive Zuckerglas whose analysis shows it to be an almost potassium-free sodium glass. We have not been able to find other references to Zuckerglas. Both the Corning Museum and the Jena Glass Works have been unable to supply further information on Zuckerglas. We suggest the possibility that the term refers to a cheap glass used in the manufacture of containers for storing candies. Soon after the publication of the voltaic cell in 1800, the academician Ritter (~1802) of Munich prepared a Zn | Glass | Cu sandwich and noted that glass acted like a moist conductor. Buff (1857) also reported experiments with such arrangements as: Carbon Powder | Glass | Liquid Zinc Amalgam Manganese Dioxide | Glass | Liquid Zinc Amalgam He found that these arrangements would charge a condenser. He concluded that the glass acted as water would act under the same circumstances. The early experimenters frequently used well or spring waters for their experiments. Even the rain water collected in cisterns contained significant amounts of electrolytes . In 1875 Professor Sir William Thomson (3)—later to become Lord Kelvin—carried out experiments on flint glass sandwiched between


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copper and zinc plates. He noted that the conductivity increased with an increase in temperature and that there were signs of chemical reaction on both the metal plates. von Helmholtz, Giese, and Meyer


In 1888 W. Giese, (4) a former assistant of von Helmholtz, reported on a flask containing sulfuric acid which he had wrapped in tin foil. The arrangement was as follows: Tin Foil | Glass | H2SO4 | Pt In this paper he described an American Virginian glass, widely distributed in the marketplace, which showed such a high conductivity that it behaved like a metal. On April 5, 1881, von Helmholtz(5) gave the Faraday Lecture at The Royal Institution. The following quote from this English language lecture will give some insights into the state of electrical experimentation in the 1880s and von Helmholtz's recognition of the importance of the high resistance problem (see Figure 1 ) . I show you, therefore, this little Daniell's cell...constructed by my former assistant, Dr. Giese, in which a solution of sulphate of copper with a platinum wire, a, as an electrode, is enclosed in a bulb of glass hermetically sealed. This is surrounded by a second cavity, sealed in the same way, which contains a solution of zinc sulphate and some amalgam of zinc, to which a second platinum wire, b, enters through the glass. The tubes c and d have served to introduce the liquids, and have been sealed afterwards. It is, therefore, like a Daniell's cell, in which the porous septum has been replaced by a thin stratum of glass. Externally all is symmetrical at the two poles; there is nothing in contact with the air but a closed surface of glass, through which two wires of platinum penetrate. The whole charges the electrometer exactly like a Daniell's cell of very great resistance, and this it would not do if the septum of glass did not behave like an electrolyte; for a metallic conductor would completely destroy the action of the cell by its polarization. All these facts show that electrolytic conduction is not at all limited to solutions of acids or salts. It will, however, be rather a difficult problem to find out how far the electrolytic conduction is extended, and I am not yet prepared to give a positive answer. What I intended to remind you of was only that the faculty to be decomposed by electric motion is not necessarily connected with a small resistance to the current. It is easier for us to study the cases of small resistance, but the illustration which they give us about the connection of electric and chemical force is not at all limited to the acid and saline solutions usually employed.



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Figure 1.

Dr. Giese's Daniell Cell.


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In 1890 (6) Georg Meyer, who had worked in Warburg's laboratory in Freiburg, gave an inaugural dissertation at Heidelberg on the topic of the electromotive force developed between glass and amalgams. In this address he described in great detail the preparation of the glass surfaces that he used. Meyer pointed out that in some of his experiments he obtained puzzling results. He noted that in the manufacture of the test tubes which he was using as cells the end closures resulted in alkali-deficient outer-end surfaces, but alkali-rich (normal composition) inner-end surfaces. Flame tests showed the outer-end surface to be alkali-deficient but the inner-end surface to be alkali-rich. He proposed a model that involved an alkali solution via a film of water (Wasser Haut) on both the inner and outer glass surfaces. (Translation from the German) These phenomena can be explained through the assumption that the outer glass wall of the test tube was made alkali-deficient when it was exposed to the direct action of the flame during manufacture and thus was not covered by an electromotively active water layer and that, on the other hand, the inner wall, which consists of alkali-rich glass, adsorbs a water layer on its surface. We would observe the electromotive force of Hg | Glass | Alkali Solution | Hg since the water on the surface of the glass forms an alkali solution. Meyer used this model, which he supported with several suitably chosen experiments, to explain the lack of electromotive activity of dry glasses. This explanation was a giant step forward in the evolution of the glass electrode and undoubtedly influenced the thinking of Cremer. Many authors give Cremer full credit for the discovery of the glass electrode. Cremer's Key Observation In 1906, at the Institute of Physiology at Munich, Max Cremer published a paper titled "On the Origin of the Electromotive Properties of Tissues, at the Same Time a Contribution to the Study of Polyphasic Electrolytic Cells"(7). This paper is considered by many authors as the announcement of the discovery of the glass electrode. He pointed out that Warburg considered glass to be a solution of silicic acid containing sodium silicate as the dissolved electrolyte and that, according to Warburg, sodium could be replaced by lithium when a strong current was pushed through hot glass. Cremer referred to the "remarkable electromotive forces of glasses" and said that if the Warburg model is correct, then this would constitute the ideal case of the semipermeable membrane. His discovery-that appreciable voltages were produced when acid was placed on one side and base on the other side of a glass membrane—was the key observation that caught the attention of other researchers.


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He described his experiment as follows: (Translation from the German) Thus I obtained in the first experiment, when I prepared the following cell: Physiological sodium chloride solution — 1/10N sulfuric acid - glass - physiological sodium chloride solution — a difference of potential of 230 millivolts, when conduction was done with physiological saline solution, in the sense that the current goes from the acid into the glass. I used a flask which gave only an insignificant potential difference between the inner and outer wall and now prepared the following cell with it: Zinc in zinc sulfate - 0.6 percent sodium chloride solution - the same plus about 0.01 N sulfuric acid - glass wall - 0.6 percent sodium chloride solution - zinc in zinc sulfate. If the glass wall had not been there, this cell, like the first, would have shown no current. I was not a little surprised when I was able to discern an electromotive force of around 190 millivolts (current from the acid into the glass). I removed the acid again and replaced it by physiological sodium chloride solution after washing the flask. The potential difference was minimal. ...When I added dilute sulfuric acid to the 0.6 percent sodium chloride solution on the outside of the flask and sodium hydroxide to the 0.6 percent sodium chloride on the inside, the electromotive force of the combination increased to 0.55 volts when I used a physiological sodium chloride solution as the acting conductor. Haber and Klemensiewicz In January of 1909, Haber and Klemensiewicz (8) presented a paper before the Karlsruhe Chemical Society which was published

later in the year in the Zeitschrift

für physikalische

Chemie

under the title "On Electrical Forces at Phase Boundaries." It is important to note that even though Haber is remembered as a physical chemist, in this study of phase boundary potentials he also had an interest in physiology. He felt that phase boundary phenomena might help explain the action of muscles. In this work he studied the systems glass | water, benzene | water, toluene | water, and metaxylene | water. Haber developed a model and a theory that explained the forces developed by acids and bases at the boundaries of electrolytically conducting aqueous phases. Haber's "conceptualization" for the glass | water interface envisioned, as reported in the thesis of Hans Schiller, (2.) was 1. that the water-wetted surface layer of glass swelled, 2. that the swollen surface layer was a solid water phase (Haber refers his readers to the publications of Otto Schott and Fritz Forster for further information on the swelling process) ,


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3. that the H+ and OH- were of constant concentration and immobile in the glass, and 4. that this kind of solid water phase must behave as a metallic hydrogen electrode. Haber and Klemensiewicz reported the following: (Translation from the German) In all cases the test gave confirmation of a theoretical law whose main characteristic is that the boundary potential changes, as does the potential at a reversible hydrogen or oxygen electrode, on both sides of the neutral point, with the logarithym of the acidity, respectively alkalinity. In the case of soft glass, the observation of the interface potentials is so easy that one can base a titrimetric procedure on this voltage. An interesting insight into this research is contained in a letter from Klemensiewicz to Malcolm Dole published in the Journal of Chemical Education in 1980 (10). We quote from the letter: I came to Karlsruhe in November 1908....I was then 22. Haber proposed to me to explore the glass electrode, the interest for this topic having been suggested to him by the earlier work of Cremer. They tried already in Karlsruhe some experiments before I came, but without success. I have been handed over the respective apparatus, consisting of a piece of broken glass —cylinder about 3 mm thick, with a tin-foil sticked around. I saw at once that such an element could never work, being short-circuited all over the moist glass surface. Although I didn't know at this stage that glass-balloons have been used by Cremer (and previously by Giese), I blew the thin bulb which remains until today the classical form of the glass electrode. I also installed a quadrant electrometer with the use of which I was well acquainted. With this arrangement I got at once positive results especially as I discovered at the very beginning the aid of steaming and soaking the glass, quite independently, of course. I applied steaming at first as a method of cleaning, being in this case reluctant to use either chromic acid or organic liquids. I also learned in the first days the need of avoiding drying out of the glassbulb and the superiority of soft over hard glass. Finally, I chose the kind of diagram for plotting the bilogarythmic curve as the most adequate way of presentation. When Haber went to see me in the laboratory after two days, I was able to show him a very good curve in HC1-KOH, with an efficiency of about 0.5V. He would not believe first that it was possible to get these results in such a short time and I had to let him look at the reading telescope that he could plot the points by himself. The experiment proceeded smoothly, so he gave himself an outbreak of enthusiasm, leaped, embraced and praised me in his cheerful manner.


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Haber and Klemensiewicz a l s o made an important contribution to the knowledge of the e f f e c t of g l a s s composition and pretreatment on g l a s s electrode response.


The Decade of the 1920s World War I disrupted the work of the great laboratories of central Europe and brought fundamental research to a halt so that the next landmark paper did not appear until 1920, when Freundlich and Rona (11) confirmed the observation of Haber and Klemensiewicz that the glass electrode acted as a completely reversible electrode against the hydrogen and hydroxyl ions and that it was completely insensitive to capillary active substances such as organic dyes. The decade 1920-1930 was a particularly important and fertile period in the development of the glass electrode into a practical tool for the chemist. A listing of seminal papers of this period is given in Table I.

Horovitz, Schiller, and Others of the Period The mechanism of the process occurring at the glass | solution interface continued to intrigue researchers. In a further study of this problem, Horovitz ( 1 2 ) and Schiller (13), out of Horovitz's laboratory, extended Haber's theory. In this extension they considered 1. that glass is a solid electrolyte in which the Na ion preferentially affects conduction and must act as a metallic sodium electrode, 2. that glass also contains a series of other metal ions so that one cannot treat the glass as a simple electrode function but must consider it a mixed electrode in which the equilibrium condition must be fulfilled for all ionic species, 3. that the glass surface will exchange ions with the solution, and 4. that in aqueous solution hydrogen ions are taken up by ion exchange, causing the glass to act as a hydrogen electrode. Schiller pointed out in his dissertation that this hydrogen-ion sensing electrode is the most important of the electrodes generated by ion-exchange. Hughes (14.) attempted to establish the limits of the glass electrode by posing the following questions for experimental answers: 1. What is the exact character of the curve representing the relationship between glass-surface potential and hydrogen-ion as measured by the hydrogen electrode? 2. Can the potential of a glass surface be used as a measure of hydrogen-ion concentration in cases where the hydrogen electrode cannot be used, as in the presence of oxidizing agents?


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3. What are the conditions under which the glass-surface potential is not a reliable measure of hydrogen-ion concentration, and what other ions influence this potential? Brown (Hi) reworked Haber's theory of potential formation at the glass electrode. He noted that the kind of glass used was of great importance and that the electrode was very promising from the point of view of the biologist. He was among the first to mention the problem of shielding and insulation when dealing with high resistance circuits. Michaelis (16) mentioned that the glass membranes acted like his membranes of dried collodion. This observation points toward the current concept of membrane electrode theory. Kerridge (17) concerned herself with measurement of the voltage of the cell. She determined the relative utility of the Dolazalek, Compton and Lindemann electrometers. She preferred the Lindemann instrument because of its portability. From the very earliest studies on the electrical behavior of glass, it had been apparent that the properties of glass were very dependent on composition. However, nearly two centuries were to pass before a significant systematic study was undertaken on the effect of chemical composition on glass electrode response. MacInnes and Dole (18) reported on January 8, 1930in what should be considered one of the landmark papers on the glass electrode—a systematic study of glass composition versus electrode response to the hydrogen ion. They formulated a number of glasses and measured (1) the potential existing in the diaphragm of the glass to be tested, (2) the resistance of the electrode, (3) the deviation from the theoretical in a buffer at pH 8, and (4) the deviation in an approximately 0.1 N sodium hydroxide solution of pH 12.75. They concluded that the best hydrogen-ion response was obtained from a glass of the composition SiO2, 70%; Na2O, 22%; and CaO, 6%. The response of Thuringer glass to alkali and alkaline earth metals prompted Trümpler (19) to propose the glass electrode as a means of determining normal potentials via the use of amalgams. He found a value of 2.72 V for sodium. An acceptable model for the mechanism of the behavior of the glass electrode was now in place. The type of glass used, the nature of the pretreatment, the other ions in the solution, and the thickness of the glass bulb were all recognized as experimental parameters requiring control. However, the formidable problems in measurement circuitry associated with the high resistance of glass still remained to be solved, and, as is so often the case in chemistry, the answer to the problem—the measurement of voltages in circuits of high resistance—was already in the literature albeit hidden in a new and poorly understood field of physics.


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The Vacuum Tube Is Applied to Acid-Base Chemistry A significant portion of the science effort during the middle and late 1800s was directed toward the problems involved in improving telegraphic communications. As a consequence of the intense interest and the resulting progress in the field of communications technology, an environment was developed that was suitable for the creation of the vacuum tube. Sir John Ambrose Fleming paved the way for the next major step forward by providing this invention-the diode-in 1904. Fleming used the diode for rectifying the alternating current generated in an antenna by incoming radio waves. The triode version of the vacuum tube was soon developed by Lee de Forest, who filed for patent coverage on October 2 6, 1906. An excerpt (20) from de Forest's description of the invention follows: It now occurred to me that the third, or control, electrode could be located more efficiently between the plate and the filament. Obviously, this third electrode so located should not be a solid plate. Consequently, I supplied McCandless with a small plate of platinum, perforated by a great number of small holes. This arrangement performed much better than anything preceding it, but in order to simplify and cheapen the construction I decided that the interposed third electrode would be better in the form of a grid, a simple piece of wire bent back and forth, located as close to the filament as possible. I now possessed the first three-electrode vacuum tube—the Audion, granddaddy of all the vast progeny of electronic tubes that have come into existence since. According to the autobiography, de Forest had trouble making suitable glass envelopes for his experimental vacuum tube. McCandless, an independent manufacturer of what in today's language would be called light bulbs, had a shop near de Forest's laboratory. When de Forest turned to him for help, he not only prepared the glass envelopes successfully but also gave de Forest many helpful suggestions on the experimental work. The advent of the triode in the communications field via a technology crossover put in the hands of all science a tool of undreamed of worth. Of course, in its early months—and yearsits wide range of uses were unrecognized. In his autobiography de Forest (21) remarks on it as follows: The Audion, in a measure, is to the sense of sound what a microscope is to that of sight. ...But when the first steps were taken in the work which eventually resulted in the Audion of today, I no more foresaw the future possibilities than did the ancient who first observed magnification through a drop of water.


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Goode Develops a Continuous Reading Titration Apparatus This new development, the triode, was not immediately used. The first report, some 16 years later, of its use in connection with the hydrogen ion was in the construction of a continuous reading titration apparatus which was published as a paper in the

Journal

of the American

Chemical

Society

in 1922.

It is inter-


esting to note that this research was done for the M.S. degree. Goode stated both in the paper ( 22) and in his thesis (21) : The investigation described in this paper has shown that the 3-electrode vacuum valve ("audion") presents almost the ideal case of a "voltmeter" which draws no current from the source to be measured, and can therefore be employed as a continuous-reading instrument for determining the concentration of the hydrogen ion. Goode recognized and reported that this was the ideal instrument for the high resistance case. Elder and Wright Develop a pH Meter However, there was another delay of several years before a paper appeared in the literature (1928) applying vacuum tube technology to the glass electrode (24). In the summer of 1928 Walter H. Wright, a young radio-ham undergraduate student at the University of Illinois, had the good fortune to take a course, Advanced Analytical Instruments, under Lucius Elder. His memories of the class are that it was wide-ranging and somewhat similar to what we would now call a "Think Tank." As a result of the interest he generated in this class and his knowledge of radio and wireless telegraphy, he was prompted to propose for a B.S. degree thesis project (25) the construction of a device for pH measurement. (The historic little thesis that resulted is held in the rare books collection of the Archives of the University of Illinois at Champaign-Urbana, Illinois.) The device would employ a vacuum tube potentiometer and a glass electrode. Then, in an amazing piece of research, he overcame both the electronics and electrode construction problems and put together a workable instrument for measuring pH. He cannibalized his one-tube radio receiver and used its audion (UV199) to build the potentiometer. He then prepared a soda-lime glass for electrode production. A portion of his account (23.) is as follows: The first attempt at pure soda-lime glass preparation was a disaster! The melt was made in a platinum dish and heated in a 20KW carbon granule furnace equipped with a tap-off transformer and protected by a circuit breaker in the power supply. I had been assured that the furnace would not melt Ferro-Silicon (approx. 1590°C) and was therefore safe for platinum (M.P. 1753°C) . I reasoned that the furnace power supply maximum could be 20KW so



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ELECTROCHEMISTRY, PAST AND PRESENT I set the tap-off transformer at the highest voltage to keep under this figure. When the breaker tripped I set the tap-off transformer at the next lower tap, reset the breaker and repeated the process. As the furnace temperature rose, the carbon resistance fell, thus drawing more current and tripping the breaker. I followed the temperature rise by observing a range of segar cones placed alongside the platinum dish. After several cycles of [the] above steps I removed the lid to observe the melt. White light came from the furnace, the segar cones had melted, also the platinum dish and its charge! One explanation was that the platinum dish ($300 worth) had been purchased during World War I and therefore might not be pure platinum. I then looked up the thesis (CA 1915) covering the original use of the furnace for preparation of Illium type alloys for S. W. Parr. The original user apparently was afraid to trip the breaker and thus never got the full 20KW available and hence did not reach the temperatures possible. In any event the contents of the furnace bottom were removed and turned over to an inorganic grad student (S. C. Ford) for platinum recovery. The next move was to use a graphite crucible and risk some impurity in the glass being picked up from the binder used in the crucible. The melt from the graphite crucible did have a slight purple color possibly due to manganese or cobalt (?). Finally, a large Nickel crucible was used resulting in a melt that was drawn into small rods with a slight brown color, probably due to a trace of dissolved nickel oxide.

Mr. W. H. Wright, after a long career with E. I. du Pont de Nemours and Co., now (1988) lives in Wilmington, DE in retirement. He still has in his possession the little UV199 vacuum tube and some of the original soda glass that he used to fabricate his electrode. Thus the glass electrode-vacuum tube pH measuring machine made its way into the literature. The novelty of the Elder and Wright study led to its early publication. Beckman Builds a Practical pH Measuring Instrument Then, as we all know, A. 0. Beckman(27) a few years later (1935) built and commercialized a sturdy and stable pH measuring device, with a two-stage amplifier, that was to make the name Beckman synonymous with pH meter. This line of instruments with improved electrodes and electronics led to papers by the score and has played a very positive role in the development of all phases of science.

In Conclusion One cannot pore over the records of this development—which delineate the many clever experiments, interminable hours of work, and seemingly endless frustrations endured by our colleagues of


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the past while enroute to the highly satisfactory solution of the glass electrode problem—without feelings of humility, joy, pride, and deepened respect for our forbears .

Literature Cited 1. Berry, A. J. Henry Cavendish. His life and Scientific Work; Hutchinson of London, 1960; p 13. Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 4, 2016 | http://pubs.acs.org Publication Date: January 1, 1989 | doi: 10.1021/bk-1989-0390.ch019

2. Buff, H. Liebigs Ann. Chem. 1857, 90, 257-283. 3. Thomson, Sir W., F.R.S. Proc. R. Soc. London 1875, 23, 463464. 4. Giese, W. Ann. Phys. (Wieri. Ann.) 1880, 9, 161-208. 5. Professor Helmholtz; XLII. J. Chem. Soc. London 1881. 39, 277-304. 6. Meyer, G. Wied. Ann. 1890, 40, 244-263. 7. Cremer, M. Z. für Biologie 1909. 47, 562-607. 8. Haber, F.; Klemensiewicz, Z. Z. phys. Chem. 1909, 67, 385431. 9. Schiller, H. Ann. Phys. 1924, 74, 105-135. 10. Dole, M. J. Chem. Educ. 1980, 57, 134. 11. Freundlich, H.; Rona, P. Sitz. Ber. Preuss .Akad. Wiss. 1920, 20, 397. 12.Horovitz, K. Z. Phys. 1923, 15, 369. 13. Schiller, H. Ann. Phys. 1924, 74, 105-135. 14. Hughes, W. S. J. Am. Chem. Soc. 1922, 44, 2860-2867. 15. Brown. W. E. L. J. Sci. Instrum. 1924, 2, 12-17. 16 Michaelis, L. Naturwissenschaften. 1926, 14, 33-42. 17.Kerridge, P. M. T. J. Sci. Instrum. 1924, 3, 404-409. 18.MacInnes, D. A.; Dole, M.J. Am. Chem. Soc. 1930, 52, 29-36. 19.Trumpler, G.; Z. Elektrochem. 1924, 30, 103-109. 20.de Forest, L. Father of Radio: the Autobiography of Lee de Forest: Wilcox & Follett: Chicago, 1950; p 214. 21. ibid. "Extracts from a paper— 'The Audion. Its Action and Some Recent Applications'—which I read before the Franklin Institute at Philadelphia, January 15, 1920."; p 477. 22.Goode, K. H. J. Am. Chem. Soc. 1922, 44, 26. 23.Goode, K. H. M.S. Dissertation: Continuous Reading Electrotitration Apparatus, The University of Chicago, 1924. 24. Elder, L. W.; Wright, W. H. Proc. Nat. Acad. Sci. 1928. 14, 936-939. 25. Wright, W. H. B.S. Thesis: pH Measurement with the Glass Electrode and the Vacuum Tube Potentiometer. University of Illinois, 1929. 26. Letter from W. Wright to C. E. Moore, November 7, 1985. Archival Document. Loyola University of Chicago, Chicago, IL 60626. 27.Tarbell, D. S.; Tarbell, A. T.J. Chem. Educ., 1980, 57, 133. RECEIVED August 12, 1988


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Development of the Glass Electrode - ACS Symposium Series (ACS

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