iVteftofe Medal
Addresm
Physicochemical Principles i n Analytical Research I. M. KOLTHOFF, University of Minnesota, Institute of Technology, Minneapolis 14, Minn. It is urged that w e continue t o cultivate analytical chemistry as a science, b o t h in education a n d i n research, lest w e awake t o a f u t u r e w h e r e scientific a n a l y t i c a l c h e m i s t s w i l l b e f o u n d o n l y i n h e a v e n for there will n o t b e a s i n g l e o n e o n e a r t h U N an occasion like this one the recipient of the medal can not help but feel that in his accomplishments he has only been an instrument in the hands of his Creator. No scientific answer can be given, and I believe ever will be given, to the question of what does determine an individual's interests, intuitions, inspirations, and creative abilities. Creative power, be it in arts, literature, or science is an endowment from the great Unknown Power, be it called God, Creator, or Fate. I t is this endowment which is the driving force in the tireless search for understanding and discovery and which also is the source of supreme happiness derived from the fruits of one's work. Truly and verily, a person with such endowments may call himself "Amor Dei." I t has been my privilege and good luck to receive most of my education from the late N. Schoorl, who taught analytical chemistry both as a science and an art. Being a pupil from the old famous Amsterdam school of van't Hoff, Bakhuis Rozeboom, and Lobry de Bruyn, it is not surprising that Schoorl stressed the scientific aspects of analytical chemistry and cultivated the feeling of an understanding of the facts. Certainly his teaching of analytical chemistry had nothing in common with the kind of cook book analytical chemistry taught in most universities in those days. Schoorl often told me that van't Hoff did not exhibit the slightest interest in analytical chemistry, a sentiment which is still shared by many physical chemists today. The reason for this poor appreciation of analytical chemistry was explained as early as 1894 by the famous German scientist Wilhelm Ostwald in his unassuming, modest booklet entitled "The Scientific Fundamentals of Analytical Chemistry." Although published at the end of the past •century, this book is still of fundamental importance, and I would like to see all students get acquainted with it, especially those who major in analytical chemistry. In the preface of "Die WissenschaftHichen Grundiagen" Ostwald states "contrary to the development which the technique of analytical chemistry has experienced is its scientific development." Consequently, Ostwald says, analytical VOLUME
chemistry occupies the position of a maidservant among the other branches of chemistry. Sixty years later we do well to remember this characterization of analytical chemistry, as there is a tendency at present to overemphasize the teaching of the manipulation of instruments, called by naïve people "instrumentation." With due respect to real "instrumentation," a subject rightfully gaining academic recognition by all scientists, it must be stated that the further development of analytical chemistry is based upon further systematic studies and applications of properties of substances, be they chemical, physical, or biological. If this is not done, analytical chemistry may relapse to the role of the maid-servant, a situation which is not cherished by most of us, even though maids belong to an almost extinct, but socially useful and financially well rewarded group. Let us fully appreciate the proper role of the analytical chemist and let us beware of a future time when all scientific analytical chemists would be found only in heaven because there would not be a single one on earth. Acid·Base Indicators I t was Schoorl who laid the foundation of my appreciation of the physicochemical and also organic principles of analytical chemistry. When I took my first course in quantitative analysis in 1913, I was greatly puzzled by the proper choice of acid-base indicators in acidimetry and alkalimetry. Before the days wrhen the concept of p H was introduced by S. P. L. Sôrensen in 1909, Schoorl in a series of Dutch papers published in 1904 made some basic contributions to our understanding of properties of indicators. Sorensen's papers still belong to the most fundamental publications on the subject of pH and indicators and are as important now as they were in those days. Clear definitions of acid-base indicators with an experimental study and interpretation of their properties were given. No less important in the same paper is the set of buffer mixtures with p H values measured with the hydrogen electrode. No wonder, that with Schoorrs guidance, Sorensen's papers stimulated me greatly. It now appeared
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possible to calculate from ionization constants of acids and bases the "neutralization curves" and to- select the ^proper indicator for the detection of the end point. My first book in the scientific field was published in 1920 on the subject "Die Théorie der Farbenindicatoren," which in its latest English edition is called "Acid-Base Indicators." For a reasonable interpretation and the further development of the analytical applications of indicators it is essential to understand the development of the theories of acidity and basicity. Most analytical work has been and still is confined to aqueous systems. For a quantitative formulation of acid-base equilibria in such systems the classical theor}' of acids and bases of Arrhenius. amended by the Debye-Huckel theory of strong electrolytes,, is still adequate. However, for a study of acidity and basicity in nonaqueous systems and especially for a correlation of the acid or basic strength of a substance in various solvents the Arrhenius theory is entirely inadequate, because it does not take into account the acid and basic properties of the solvent. This is one of the main features of the more modern theory of Brônsted-Lowry (1923) of acids and bases. This theory simply states that an acid is a substance which can split off a proton and a base is a substance which can combine with protons. Free protons do not exist to a measurable extent in any solvent. In order to get dissociation of an acid in any solvent, the latter must be a base, it must have an affinity for protons. The so-called degree of dissociation of an acid in a solvent is therefore determined by the intriasic acid character of the acid, that is its tendency to split off protons, and by the basic character of the solvent, that is its affinity towards protons. An acid which is weak in water becomes a strong acid in a solvent which is a much stronger base than water, for example, liquid ammonia. On the other hand uncharged compounds which are weak bases in water become strong bases in solvents which are much stronger acids than water is, for example glacial acetic acid or sulfuric acicl. The analytical significance of the acid-base properties of the solvent are clearly demonstrated by the classical studies of Conaht and Hall (1931) in glacial acetic acid as a solvent. It was shown potentiometrically that substances like pyridine and aniline, which are very weak bases in water, can be ti835
trated like strong bases in glacial acetic acid. Systematic studies of acid-base properties in nonaqueous solvents are still lacking. With certainty it can be predicted that such studies should yield results which are of direct analytical significance. Substances which are too weak acids and bases in water t o be titrated satisfactorily in water can be titrated in appropriate solvents. Systematic studies of the above nature are on our program, and it is fully realized that they \yill not be quite simple. Most salts are strong electrolytes in water and are completely dissociated in this solvent. With a fair approximation their dilute solutions can be considered as ideal, that is, as a first approximation concentrations can be written instead of activities. This situation no longer holds true in solvents of small dielectric constant. Even in a solvent like nitrobenzene with a dielectric constant as high as 35, the dissociation of electrolytes which are strong in water is very incomplete as was shown first in the classical studies by Kraus and Fuoss. Marked deviation from ideal behavior is found even at very high dilutions, and a knowledge of activity coefficients ef all i®ns and of dissociation constants of all electrolytes is required in the quantitative formulation of acid-base equilibria in solvents of low dielectric constant. An* additional difficulty is our limited supply of suitable indicators. Admittedly f we m a y have some 400 to 500 substances which are suitable indicators in t h e entire p H range which can be covered in water as a solvent. But with solvents which are stronger acids than water is, in which we are dealing with so-called "superacid" solutions, or in solvents which are much stronger bases than water is, where we have "superbasic" solutions (the "super" with reference to water) our supply of suitable indicators is very limited. In solvents with superacidity some of the indicator bases used by Hammett in his classical studies of the "acidity function" should be useful for analytical purposes, but much research remains to b e done in order to find an adequate supply of indicators which are suitable for acid-base studies in nonaqueous solvents. There is n o doubt in my mind that studies of the above nature will yield rich dividends to analytical chemistry, especially to organic quantitative analysis. Lewis
Acid'Base
Theory
This very brief review of acid-base titrations in various solvents would be woefully incomplete without mentioning the G. N . Lewis theory of acids and bases. According t o Lewis bases are donors of a pair of electrons, and acids are acceptors of a pair of electrons donated by a base. Bases have at least one pair of unshared electrons; when they react with acids, a coordination compound is formed. The
836
" Lewis theory is a very general one; it is mxich broader than the Bronsted-Lowry theory, which confines itself t o the transfer of protons comparable to the electrochemical theory of oxidation-reauction wfciich confines itself to reactions involving t h e transfer of one or more electrons. T b e question has arisen whether the Lewis theory should be generally adopted and t h e Bronsted-Lowry theory dropped. In spite of certain apostles of the Lewis theory i t must be maintained that the Bronsted and Lewis theories are not contradictory, b u t t o the contrary, they supplement each other. Strictly speaking, the substances which belong to the claps of compounds containing a proton which c a n be split off and which have been called acids for centuries would not be called acids according to the Lewis theory. The reason is that the proton c a n not be doubly coordinated. T h e su"bstance HC1 can be considered as the neutralisation compound of the proton, wtiich i s a Lewis acid, and the chloride ioxi, which is the base. In order t o h a v e t h i s neutralization product, which is called hydrochloric acid, act like a Lewis acid, w e must assume that the primary reaction between HC1 and a base consists of the formation of a coordination compound; i n other words, it must be assumed th.at.the proton can be doubly coordinated. TInuswe arrive at the conclusion that the large group of substances, classified by the time-honored name as acids, are not acids according to the Lewis theory. It is j u s t this group of substances with which thte Brônsted-Lowry theory is concerned. Therefore, there is more than ample justification for the proposal to maintain both th_e Lewis and the Bronsted-Lowry theories of acids and bases. The late Professor Lewis w a s in complete agreement with this pr-oposal. In fairness to t h e Lewis theory, it m a y b e stated that t h e acid properties of a Bronsted acid can be accounted for by considering it as the neutralization product of the Lewis acid proton with a base. I n the reaction of such a neutralization product with bases we are dealing with a replacement of t h e original base in the "neutralization product" by another one: ( 0 · Ι Ι 2 0 ) + 4- NH 3
> (H-NH,) + + H 2 0
Formally, this presentation is identical with thie proton ^transfer reaction in the Bronsted sense. The objection to the above formulation, however, is that we have t o call a Bronsted acid a neutraliza t i o n product in the Lewis theory. Undoubtedly the last word has not been s a i d yet about the mechanism of an acidbase reaction. I t is, to say the least, qxiestianable whether the primary re action of Bronsted acids writh bases in volves the direct transfer of a proton. T h e primary reaction between the acid a n d the base may consist in the formation o £ a hydrogen bond. In basic solvents
CHEMICAL
of high dielectric constant the acid reacts with the solvent base with primary formation of a hydrogen bond, the latter dissociating immediately with the forma tion of solvated protons and the conjugate base of the acid. However, in solvents of low dielectric constant acids and bases may react, neither in the Lewis nor in the Bronsted sense, but by formation of a stable addition product through hydrogen bonding. Even in aqueous medium re action through formation of a hydrogen bond often occurs. We only have to consider the interaction between water and ammonia. Without more detailed knowl edge of the hydrogen bond it seems safe to expand the Bronsted definition in the following way: Acids are substances which can transfer a proton to a base or which combine with a base by formation of a hydrogen bond. You may raise the question why an analytical chemist should be concerned about these theories at all. Over and over again it has been my own experience that only by an understanding of the reactions we make use of in quantitative analysis can we extend and expand the scope of analytical chemistry. T o be sure some one may find empirically that acetate or an amino-acid like glycine can be titrated like strong bases in glacial acetic acid with a standard solution of perchloric acid in the same solvent. However, in order t o develop systemati cally the entire field of acid-base titra tions in nonaqueous solvents, an under standing of the Bronsted-Lowry theory, the modern theory of strong electrolytes, etc., are required. Also a proper appreciation of the Lewis theory is of importance t o the analytical chemist, as the following example illus trates. T h e yellow compound dimethylaminoazobenzene, often called butter yellow or methyl yellow, has been used for many years as an indicator for hydro gen ions which combine with the azo compound to form red-colored cations. This reaction had always been considered a s a specific one for hydrogen ions, until G. N. Lewis broke away from the "cult of the proton" and showed that in aprotonic solvents an indicator like methyl yellow reacts with a (proton-free) Lewis acid like boron trifluoride or antimony chloride with the formation of a red neutralization product. Thus methyl yellow does not only react with protons but with all Lewis acids if they have the proper strength. T h e analytical replica tion or application of the above illustra tion is self-evident. It should be possible t o titrate Lewis acids in appropriate non aqueous solvents with the proper bases when a suitable indicator is used. Acidity and basicity in nonaqueous solvents i s an attractive research field for the ana lytical chemist. Considering the success derived from calculation of acid-base equilibria and properties of indicators, I extended the
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application of results obtained from calculations of equilibria to precipitation, complex formation, and oxidation-reduction reactions. The ultimate outcome was a book entitled "Volumetric Analysis," published in German in 1926 and dedicated to my teacher Schoorl under the motto "Theory guides, the experiment decides." I still fully subscribe to this motto. When I wrote the first edition of this book, I did not dare and I still hesitate to challenge my colleagues by proposing
a change in the name of the time-honored classification "Volumetric Analysis" into "Equivalization Analysis." The word "volumetric analysis" really is a misnomer and would be appropriately applied to gasometric methods of analysis in which volumes are measured. In volumetric analysis with weight burets no volumes are measured at all. Electrownetric Methods In my studies of titrations I did not confine myself to the visual observation
of the end point. Inspired by a paper by J. H. Hildebrand in 1913 on titrations with the hydrogen electrode and the work by the Swiss chemist Dutoit, I became more and more interested in the electrometric type of titration. In order to avoid confusion I proposed to make a distinction between potentiometric and conductometric titrations. In 1923 a little monograph appeared in German on eonductometric titrations which summarized the work in this field. In 1924 I visited this country and gave some talks on elec-
vehement exponent of the principle that analytical chemistry must be grounded in and preceded by fundamental scientific knowledge if it is to be truly a science rather than "the hand-maiden of the describes as "fabulous by academic standsciences," Kolthoff has ever sought the ards." However, KolthofFs devotion theoretical basis of analytical proceto fundamental investigation and redures as a fundamental end. However, quirement of maximum personal and scientific freedom were not adaptable to his virtuosity in developing experimental procedures to prove the basic theories has industrial occupation, and he declined been demonstrated on many occasions. without hesitation. He remained at Kolthoff's friends know, him as a man Utrecht as a teacher and when, in 1918, the Dutch laws were altered, received his of outstanding mental and physical vitality. His enthusiasm for intellectual Ph.D. in chemistry upon the submission activity has been exercised not only in of a thesis titled "Fundamentals of Iodimhis professional field of chemistry but as etry." He even practiced a little phara thinking and acting member of the macy, or at least toxicology. Kolthoff is national and world community. A a skilled raconteur, and one of his favorite stories is a pungent account of his first "middle of the road" liberal, a natural compromiser, and constitutionally oppostmortem examination. The subject posed to extremes of thought, he has been was no less than Mata Hari's daughter the target of both political wings. His who had died mysteriously shortly after unceasing efforts for the internationaliinheriting her mother's not inconsiderzation of science and for the broadening able ill-gotten gains. The chemist could of human liberties throughout the world detect no unaccountable poison but mainhave been recognized repeatedly. tained that his report could have been His enthusiasm and natural exubermuch more conclusive if the surgeon had ance have found physical release in a used anything but bichloride of mercury whole catalog of sports including riding, as a disinfectant during the dissection. tennis, swimming, hiking, rowing, and By 1924 KolthofFs increasing reputaskiing. His favorite is probably riding tion led to a speaking tour of Canada and which he learned along with his chemistry the United States, and in 1927 he acfrom Prof. Schoorl. A favorite anecdote cepted a temporary appointment at the of the University of Minnesota campus is University of Minnesota, which ultithe tale of Kolthoff's convalescence from mately resulted in his permanent estaba recent spinal operation. While still lishment in this country. His relocation, confined to his bed he had a special telehowever, did not disrupt the orderly sequence of research investigations which . phone installed so that he could get hourly reports from his laboratories. had been begun almost simultaneously Once released from the hospital he was with his collegiate education. His first often seen being helped from his crutches investigations of the theory of acid-base onto a horse for his daily ride. reactions and the mechanism of other analytical reactions evolved into the de"Piet" Kolthoff (even he is not sure velopment of the electrometric methods. where the nickname came from) seems to The studies of electrometry centered first come pretty cjpse to satisfying everyon conductometric methods and then body's specifications for a well-rounded progressed to potentiometric and ultiscientist. He has done sound basic mately amperometric techniques. Even work but always with an eye to its ultihis wartime excursion into the mechamate practical application. He is obnism of emulsion polymerization, which viously aware of the social implications still continues, revolves around the acof a technological society and has accurate analysis of the various phases of tively worked for his social beliefs. And the reaction mixture. he has a good time, too. He doesn't say that he has been able to do all this beKolthoff's co-workers see him as the cause of his carefully maintained bachelorembodiment of his favorite motto: hood. "theory guides, experiment decides." A
Isaac Maurits Kolthoff I N Holland in 1911 fluency in English, French, and German was not considered adequate linguistic preparation for academic work in the physical sciences. A special examination in Latin and Greek was also required. Isaac Maurits Kolthoff, graduating from the Hoogereburger (High) School in that year, did not have an acquaintance with these venerable languages so he chose to exercise an already well-developed interest in the field of chemistry by studying chemical engineering at the University at Delft. However, 14 days in this curriculum convinced him that he had little liking for the solid year of mathematics which introduced the course, and he returned home to reconsider his plans. Under family pressure to resume his studies or "go into business" he enrolled in the school of pharmacy at the University of Utrecht. The title of pharmacist is not conferred lightly in Holland and climaxes a six-year course of intensive study. Pharmacy students are encouraged to initiate independent research projects early in their training, and in 1913 Kolthoff published the first of his scientific articles. Submitted to the famous analytical and microchemist Nicholas Schoorl for review, the young scholar's maiden effort drew the comment, "Kolthoff, your Dutch is terrible. Since you apparently are going to write a lot of papers you will simply have to improve your style." Apparently the advice was well taken for one of Kolthoff's colleagues recently said that if Kolthoff had never faced a class he would still be a great teacher because of the lucidity and explicit exposition of his seven books on analytical chemistry. Schoorl's prophetic assumption also proved justified for since that first maligned effort more than 600 publications have appeared under the Kolthoff name. When he had completed his course of study, his diploma said "pharmacist," but his adequacy and reputation as a chemist was attested by an offer to assume the chemical directorship of the Bandoeng Works in Java at a salary that he
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trometric titrations, a subject well ap preciated here, thanks to the contributions of J. H. Hildebrand, H. H. Willard, N. II. Furman, and others. It has been my good luck to find Prof. Furman willing and anxious to be the coauthor of a mono graph," Potentiometric Titrations," ( 1927) a third edition of which is in preparation with D. N. Hume as a third coauthor. In retrospect, I believe that it is fair to state that in the past 20 years not much has been added to the fundamentals of potentiometric and conductometric titra tions although it is readily admitted that with the recent rapid advances in instru mentation the practical performance of this type of titration has been greatly facilitated. Guided and inspired by the pioneer work of J. Heyrovsky of Charles Univer sity, Prague, J. J. Lingane in 1936 de cided to choose the fundamentals of polarography as the subject of his doctor's thesis. The outcome was not only that Lingane has become a recognized leader in this field, but the subject also directed our attention to another type of electrometric titration for which I coined the word "amperometric" titrations.. One attractive feature of amperometric titra tions is that mant^ determinations can be made accurately even at high dilutions. A number of organic reagents have proved to be very suitable for the determination of a large number of inorganic cations. As a side line of a study of electrolysis phenomena at the dropping mercury electrode, H. A. Laitinen in 1939 started a simitar study at stationary platinum electrodes of various shapes and finally at the rotated microplatinum wire electrode. The unique properties of this rotating electrode are only slowly being recognized. It is no rash s atement when I say, that in my opinion, amperometric titrations with the dropping mercury electrode and the rotating platinum electrode as in dicator electrodes will become at least as much practiced as potentiometric titra tions are at present. A great number of titrations await further study by the amperometric technique. A systematic study of the first reaction products in the precipitation of various metals with organic reagents is now possible, especially with dropping mer cury as the indicator electrode. Several organic reagents have been found suitable in the amperometric titration of a number of inorganic ions,' especially, when present in micro- and submicro quantities. Other important reactions, like that between sulfide or ferrocyanide and metal ions can be studied simply and tested for their analytical applicability. It has been shown, for example, that upon ampero metric titration of a mixture of copper and zinc with sulfide under suitable conditions copper precipitates quantitatively before zinc sulfide starts to separate. We just have been talking about one aspect of'precipitation methods in titrim838
etry. It is not surprising that an an alytical chemist should become interested in the various properties of precipitates. Solubility, size, and purity of precipitates are of essential importance in gravimetric analysis. Adsorptive properties of pre cipitates are especially important in con nection with the use of adsorption in dicators in precipitation methods in ' 'volumetric analysis" while the colloidal properties of precipitates are of funda mental importance in nephalometric and turbidometric determinations. It was my good fortune to have been introduced into the fundamentals of colloid chemistry by nobody less than H. R. Kruyt of the University of Utrecht, a most inspiring teacher and a world leader in this field. The course in colloid chemistry has been the background of and the inspiration for my work in the field of precipitates. Aging of Precipitates Time docs not allow a discussion of coprecipitation, postprecipitation, and ad sorptive properties of precipitates. How ever, I would like to dwell briefly upon one aspect of the subject, that is, aging of precipitates, either ' when in contact with a liquid phase or in the dry state. The subject is of direct analytical im portance, because frequently it is found that a considerable purification of a pre cipitate occurs upon aging. Another fortunate incident in my scientific life was to find Charles Rosenblum, one of S. C. Lind's students, interested in the application of radioactive isotopes to a study of aging of precipitates in the pres ence of a liquid phase. It soon appeared that a microcrystalline precipitate of lead sulfate formed by rapidly adding together 0.1 M lead nitrate'and 0.1 M alkali sulfate was subject to a great number of recrystallizations when allowed to age in the supernatant liquid. The occurrence of such rapid recrystallizations appeared to be a general phenomenon. Ε. Β. Sandell studied the aging of calcium oxalate, H. Yutzy and others that of silver halides with radioactive halogens as indicators, G. E. Noponen and others studied the aging of barium sulfate under varying conditions, and F. T. Eggertson that of lead chromate. Based on refined x-ray measurements carried out by Walden and co-workers at Columbia University, it may be concluded that small amounts of coprecipitated impurities are incorporated in the host crystal in the form of a solid solution. These solid solutions are not in equilibrium with the surrounding liquid and seem to be responsible for continuous recrystallizations of the primary precipi tate. During the recrystallizations the impurities enter into the liquid phase where they remain. Thus, it is seen that in the presence of a liquid phase the recrystallizations of highly imperfect crys talline precipitates ultimately lead to a considerable purification of the primary precipitate. The analytical implications CHEMICAL
of the purification upon aging are selfevident. I t is not always necessary to have a liquid phase present in order to ac complish these recrystallizations; they may be brought about thermally in the dry state. Dry precipitates with a low melting point, like the silver halides are subject to drastic aging when kept at room temperature. This was first shown by Λ. S. O'Brien who studied the exchange between radio active bromine in the gas phase and bro mide ions in freshly prepared dry silver bromide. I. Shapiro arrived at a more complete understanding of the mechanism of this thermal aging of silver bromide by measuring changes of the electrical con ductance, specific surface, compressibility, apparent volume, and other physical pr^erticf. Most of the ordinary types of precipi tates like barium and lead sulfate, lead chromate, and lead molybdate have too high a melting point to allow thermal aging at room temperature in the dry state. With such precipitates thermal aging can be brought about by heating to higher temperatures. A preliminary study with barium sulfate was started by Wm. McNevin -with a very fine, microscopi cally undefined product of barium sul fate. Upon heating at 800° C. or at higher temperatures, well developed rhombohedrons were formed as a result of the thermal recrystallizations. Copre cipitated impurities like sodium sulfate were expelled from the primary precipitate and could be removed simply by washing the heated product with water. Studies of thermal aging of silica by G. Cohn and I. Shapiro have contributed some under standing of the complex reactions which take place. However, more intensive studies of thermal aging of analytically more important precipitates are planned in order to arrive at an understanding of the phenomena and an appreciation of the practical analytical importance of the* results. Certainly, studies of the solid state deserve the attention of the ana lytical chemist. Up to this point I have talked briefly* on research started before the war. Int December 1942 I voluntarily became a. scientific war casualty. At that time we· were assigned by the office of the RubberDirector a project for the development of* analytical research methods to be used in. a study of the emulsion polymerization· of butadiene and styrene. This assign ment illustrates the historical role of" analytical chemistry in providing the· physical and organic chemists with methods which are necessary in systematicstudies of an understanding of a new field with involved reactions. Naturally, our* group did not confine itself to the develop ment of the analytical methods, but we took part in applying the methods to an understanding of the kinetics and mecha nism of emulsion polymerization. From the analytical viewpoint it is* gratifying to me that this "rubber reAND
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search," which has interfered and is still interfering so much with my prewar research, has led to the exploration of the application of another physicochemical principle in analytical chemistry, namely of reaction kinetics, which had been almost completely neglected. Based upon the difference in rate of reaction between external and internal double bonds with perbenzoic acid, T. S. Lee developed a method for the determination of the amount of 1,2-and 1,4-addition in rubber. Further systematic studies by Lee have shown now that the difference in reaction rates can be made the basis of a method of analysis of mixtures of two compounds which contain the same reactive group towards a given reagent. Thus, for example, it is possible, now, to determine .simply the composition of a mixture of two esters (rate of saponification with sodium hydroxide) or of two compounds containing a carbonyl group (rate of reaction with bisulfite, or rate of decomposition of the bisulfite addition compounds). Undoubtedly the principle will become quite generally applied in quantitative organic
analysis when dealing"with a mixture of two compounds which contain the same reactive type o f group towards a given reagent. There is another field of reaction * kinetics, that o f chain reactions, which proves to be of considerable importance in the interpretation, and the possible elimi- . nation of "induced reactions" which frequently are the source of a great nuisance in analytical chemistry. As an example, let me briefly discuss the determination of traces of organic peroxides in various organic compounds, like oils and fats, monomers, rubber, ether, aldehydes, etc. Classical methods for the determination of the traces o f peroxides are based on their reduction with ferrous iron. Upon systematic investigation it appeared that in the presence of oxygen two to three times more iron could be consumed than corresponds to the stoichiometric amount. This is attributed t o "induced" oxygen oxidation of trie ferrous iron. On the other hand, in t h e absence of oxygen, less ferrous iron i s consumed than corresponds to t h e stoichiometric amount.
Smith Receives Hillclii and Prize À STAFF* REPORT JLRESENTATION of the
1948 Hillebrand
Prize .to Edgar Reynolds Smith, chief of the physical chemistry section of the National Bureau of Standards, highlighted the annual dinner meeting and dance of the Chemical Society of Washington, local section
of
the
AMERICAN
CHEMICAL
SOCIETY. Duncan A. Maclnnes, close personal friend and one-time professor of Dr. Smith at MIT's graduate school and who is presently associated with the Rockefeller Institute for Medical Research, delivered an address, "Dr. Edgar R. Smith and His Scientific Background/' Dr. Maclnnes, pointed out that Dr. Smith was of the school of physical chemists originally initiated by Arthur A. Noyes. Dr. Noyes, on his return from Germany, where he had completed his doctorate under Ostwald in 1890, joined the staff at M I T . In 1903 he established MIT's research laboratory of physical chemistry, one of the first in the United States for the development of pure science. Of a group of approximately 50 physical chemists whose studies under Dr. Noyes had given them an opportunity to learn of his high standards of precise thinking and precise measurements was E. W. Washburn. Dr. Maclnnes in turn studied under Dr. Washburn prior to joining MIT's staff, where Dr. Noyes was still spending a portion of his time. Following completion of his undergraduate work, during which time his physical chemistry course was still under Dr. Noyes' direct supervision, Dr. Smith
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continued his graduate work a t M I T in this same field under Dr. Maclimos' direction. It was here that Smith initiated his studies on the moving boundary method for determining transference numbers, as well as studies on measurements o n the potential of liquid junctions between solutions of electrolytes. Dr. M a c l n n e s further stated that such studies are part of t h e underlying stratum of pure science upon which applied sciences such as medicine and engineering are built. Edgar ft. Stnith receives president of the section,
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This is attributed to "induced" decomposition of the peroxide. The use of the word· "induced" reaction admittedly is a very convenient one, especially if we are ignorant of its nature. Was it not Goethe, who said: "denn eben wo Begriffe fehlen, da stellt ein Wort zur rechten Zeit sich ein"? Systematic investigations by A. I . Medalia have clarified the mechanism o f the induced reactions, which involve chain reactions and which occur in the over-all reaction between ferrous iron and peroxides. An understanding of those reactions showed the way how to eliminate or greatly decrease the extent of the i n duced reactions under consideration. In conclusion the question may b e asked: "Quo Vadis," where do we go i n analytical chemistry? Considering only the academic side of the question m y answer is : continue t o cultivate analytical chemistry as a science, both in education and in research. Only in this way can w e maintain the position of importance and recognition which w e have conquered after the period of decline at the beginning of this century.
Dr. Smith's 23 years' work at the National Bureau of Standards have been of t h e solid, unsensational type in pure science. In addition to his transference numbers studies, which are essential for an understanding of solutions of electrolytes, D r . Smith has done other important pioneer work. Dr. Maclnnes characterized Smith as a quiet, hard wrorker, with persistence and ingenuity and a love of accuracy o f measurement. Presentation of the award was made b y I. C. Schoonover, of the N B S , immediate past president of the Chemical Society of Washington. C. E. White, of the University of Maryland, presided at the meeting.
Hillebranfl Prise certificate from C. E. White, as Past President I. C. Schoonover, looks on
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