T H E J O U R N A L O F
PHYSICAL CHEMISTRY Registered i n U.S, Patent Office 0 Copyright, 1979, by t h e American Chemical Society
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VOLUME 83, NUMBER 11
MAY 31, 1979
The First Infrared Spectrometer Harold Gershinowitzt The Rockefeller University, New York, New York 10021 (Received September 5, 1978)
An anecdotal account of the construction of the Harvard Chemistry Department’s first infrared spectrometer during 1936-1938 is presented.
The title refers to the first infrared spectrometer of the Harvard Chemistry Department. For 10 years, from 1937 to 1947, infrared spectra a t Harvard were obtained on “a somewhat crude but effective semi-automatic infrared spectrometer-which saved much time over conventional equipment xn this field and was used to investigate the molecular vibrations of simple polyatomic molecules”.l The publication which described this instrument2is laconic and matter of fact. As in practically all reports of research, between the lines are many adventures and misadventures, sorrows and joys. None of them is of particularly great moment. It is only because this spectrometer was a very special first for Bright Wilson that it seems worthwhile to fill in for this Festschrift some of the empty spaces. Besides, nostalgia seems to be one of the “in” emotions these days. When this story begins, Bright Wilson, 27 years old, had already established a. reputation as an outstanding theorist. He was one of the rare theorists who are not satisfied to work with the data of others and to wait until someone else has experimentally verified or disproved their predictions. For him experiment and theory were inextricably linked. It was the spring of 1936 when I received a letter from George Kistiakowsky asking whether I would be interested in corning back to Harvard as a research assistant to Bright,, who had just been appointed an assistant professor. George had offered to share his Milton Fund grant with Bright in order to provide a stipend for a research assistant. In the books of the accountants I would be responsible to both, but in fact I would be expected to spend all my time with Bright What we were to do was design, build, and put into operation ,an infrared spectrometer. I accepted with alacrity. Although I had never been anywhere near 0022-3654/79/2083-l363$01 .OO/O
an infrared spectrometer I had the utmost confidence in George’s judgment. It my two years of experimental research with him he had taught me a lot but also had made it abundantly clear that he did not consider me one of the world’s greatest experimentalists. If George thought that I could build an infrared spectrometer, who was I to cavil? Although we did some preliminary planning by correspondence actual work began in July when I arrived in Cambridge. Bright and I were only slightly acquainted. I had left Harvard in June 1934, before he arrived to take up his appointment as a Junior Fellow. We had met only occasionally since. It turned out that we were completely compatible. Although the primary responsibility for the actual construction of the spectrometer was mine, all details of design and procurement were worked out in such close cooperation that it was almost impossible to say who originated which aspect. I can remember no important differences of opinion. Lest this be attributed to a roseate view of the distant past I assure the reader that I distinctly remember major disagreements with all three of the mentors with whom I worked between 1931 and 1936. In what follows the we is not an editorial we, it means Bright and I. I was given a laboratory in Mallinckrodt basement, the distinguishing feature of which was a concrete pier independent of the building, of which more anon. As far as equipment was concerned we were starting from scratch and with limited funds. One must remember that 1936 was about the middle of the depression and long before the era of government grants. I was well acquainted with the possibilities for finding surplus or unused equipment in the Chemistry Department. Bright managed to ingratiate himself with the Physics Department with the
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The Journal of Physical Chemistry, Vol. 83, No. 11, 1979
spectacular result of finding a thermopile which had been made by Coblentz himself about 1915. Professor Theodore Lyman, then still active and head of the Physics Department, gave Bright a slit which he had used in his discovery of the Lyman series of hydrogen in the far ultraviolet. One must remember that in 1936 infrared was still largely the turf of physicists so that this physics department connection was of great value for advice as well as for equipment. Other apparatus of less distinguished or a t least less distinguishable origins soon gave the laboratory the cluttered look of a place in which work was really being done. Prior to this process of acquisition had been, of course, the choice of an optical system for the spectrometer. We decided on a Wadsworth-Littrow mounting in order to facilitate the use of several different prisms without readjusting and recalibrating the optical system. To use this system in the way we planned, it was essential that the surface on which the prisms would stand and the mechanism for rotating this surface be machined with the utmost precision. Bright decided that we had to go all out for this part of the equipment and allocated the major part of our funds to it. To our great good fortune, Bright found that the Physics Department shop had, in the person of D. W. Mann, one of the nation’s best instrument makers. He did a superb job for us in record time and also made an exit slit curved to match the exit beam. A few years later Mr. Mann was to use his skills in a much more important task, the making of cavity resonators for the radar of World War 11. Another consequence of the choice of the mounting and of the amplifying system we proposed to use was the need for many front surface mirrors which had to be flat to a quarter wavelength of sodium light. Optical flats were expensive. I no longer remember who tipped us off that good quality plate glass was very flat indeed. All one had to do was buy a sheet of plate glass, have it cut into squares of the required dimensions and then check each of the squares against a standard optical flat in an interferometer. We found that for many of the squares only a slight amount of grinding and polishing was needed to make acceptible flats. One window size sheet of plate glass gave us an ample supply of flats for mirrors. My attempts to silver them were disasters but having that done outside was not expensive. The sodium chloride prism and windows were no problem. Large crystals of rocksalt were readily available and inexpensive. A razor blade and a mallet were the only tools needed to make windows of any desired thickness. A few manipulative tricks were soon learned. No polishing was necessary. One unexpected consequence of my window making was the discovery that the Very Rich, who are often very generous with large amounts of money, can be very careful about small amounts. One day I was standing at my workbench cleaving rocksalt when Albert Sprague Coolidge walked in and watched me for a while. When I stopped to change a razor blade he asked what I did with the old blades. He explained that he had bought a razor blade sharpener which worked so well that by the time a blade was past resharpening for shaving he could no longer remember where he had put the rest of the package. I showed him where I put the used blades and assured him that he could have one to try and if satisfactory he was welcome to as many as he wanted. While optical quality glass and rocksalt posed few difficulties, KBr was another matter. Fortunately Bright had M.I.T. connections also and discovered that Professor Stockbarger was just putting the finishing touches on a
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process for making large crystals of alkali halides. When asked whether some KBr would be available he kindly offered to give us several crystals. These were too precious to be handled in an amateurish way so we had a prism and windows cut and polished by professionals. By the autumn of 1936 there was enough equipment on hand to start putting things together. During this period the advice, encouragement, and occasional assistance of George Kistiakowsky were of inestimable value. One of the first things we did was to assemble the galvanometer (a Moll of uncertain age and antecedents) and amplifying system. In the paper describing the spectrometer we say merely that it was “mounted on a concrete pier which is independent of the building.” The pier was indeed independent of the building and did not react to slamming doors or running in the halls but it definitely was not independent of the rest of the universe. The undamped galvanometer was responding to a slow vibration of low amplitude. The period was on the order of seconds. The maximum of amplitude also had a period, of 10-12 h. Bright and I tried to correlate the vibrations with phenomena that might be expected to show such a period, such as, for example, traffic density on Oxford Street and the movements of subway trains in Harvard Square. In desperation we decided half-seriously that the pier went down to bedrock and that it was responding to the beating of waves on the rocky coast of Massachusetts. The maxima of amplitude would then have been due to the tides. Since our objective was infrared, not geophysics, we consulted the literature and mounted the galvanometer in such a way as to reduce the unwanted motion. In later years, when the sensitivity of the infrared detector was much improved, it was found necessary to install more elaborate damping devices. From then on the assembly of the equipment proceeded without incidents worthy of recall. By the spring of 1937 we had an instrument still incomplete but ready to be tried in the rocksalt region. We saw a chance for a scoop. George Kistiakowsky had under way a long term project for the synthesis of organic compounds and the measurement of their heats of reaction. Ketene had just been prepared in high purity. We could find no record of its infrared spectrum although its Raman spectrum had been measured. The simplicity of its structure made it a beautiful candidate for theoretical analysis. Ketene was a nasty material to handle. It showed a deplorable tendency to polymerize on the windows of the absorption cells. We learned how to make it behave and rushed into print with a note on the infrared spectrum in the rocksalt region3 Sad to say, a little while later a paper by Thompson and Linnett4 appeared which gave the calculation of the force constants on the basis of the Raman spectrum alone, since our results had not yet reached them. A positive result of this coincidence of interests was the arrival of Jack Linnett a t Harvard the next academic year as a visiting fellow, Linnett, who went on to become vice-chancellor of Cambridge University and was elected president of the Chemical Society shortly before his untimely death in 1975, always regarded his association with Bright and George as of major significance to his subsequent career. By the end of 1937 the spectrometer was essentially completed and we sent in its description to the Journal of Chemical Physics in January 193fi2 One more set of measurements remained for me. George and his men now had pure samples of cis- and trans-butene-2. Bright and I decided to do the Raman and infrared of these even though the molecules were a bit complicated for a theo-
The Journal of Physical Chemistry, Vol. 83, No. 11, 1979
Component Discrimination in Acid-Base Titration
retical analysiis. I experienced no problems in obtaining the spectra but when Bright looked a t them he said that there was something wrong. Even a superficial estimation of the effect of symmetry on the spectra showed that lines were appearing that had no right to be there. A careful review of the path of the samples from the makers to the absorption cells shovved that somewhere they had been interchanged and that what had been labeled as cis was trans. This was probably one of the first applications of infrared and Raman spectra to identification of structural isomers. A check with a new indubitable sample of one of them showed that now everything was correct and we published my last contribution to the projectU4 I left Harvard in May, 1938. From the summer of 1937 on the ranks of Bright’s post-docs had been increasing steadily, Bill Avery from Harvard itself and Jack Linnett, Bryce Crawford, and Fred Stitt as visiting fellows. I left
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my baby in their competent hands for improvement and development. Built by two amateurs from salvage equipment, it looked clumsy and ungainly, but it worked. T o nontechnical visitors who were impressed by the number of coordinated moving parts I would explain that the magical results were obtained by strings and mirrors. Forty years later it still seems like magic to me.
References and Notes (1) E. Bright Wilson, Jr., and J. E. Ross, Annu. Rev. fhys. Chem., 24, l(1973). (2) H. Gershinowitz and E. Bright Wilson, Jr., J . Chem. Phys., 6, 197 (1938). (3) H.Gershinowitz and E. Bright Wilson, Jr., J. Chem. fhys., 5, 500 (1937). (4) H. W. Thompson and J. W. Linnett, J . Chem. SOC., 1384 (1937). (5) H. Gershinowitz and E. Bright Wilson, Jr., J . Chem. fhys., 6,247 ( 1938).
Componerit Discrimination In Acid-Base Titration William E. Gordon’ bepatfment of Chemistry, The Pennsylvania State University, McKeespot?, Pennsylvania 15 132 (Received October 16, 1978) Publication costs assisted by The Pennsylvania State University
The paper cites a growing literature on determining chemical parameters in a solution by curve fitting, where makeup of the solution, and hence the governing functions, are known. The purpose here is to determine these quantities from titration data for an unknown solution. The method depends on an additive form of the titration function based on a device discovered by Simms. This eliminates protonicity, and makes number of components (terms) the sole determinant of functional form. The method, then, consists in finding the number of terms in the function needed to obtain a best curve-fit. Functions with one term, two terms, etc., are fitted until indicators show that a limit has been reached. This occurs when the fitted curve falls within the scatter range of the data. The components of pure compounds, such as citric acid, are cleanly separated, but mixtures for which pK values lie close together are not resolved completely. An analysis shows that the limit of resolution for two components is given by XzApP = 4apH, where Xz is fraction of minor component, ApK the pK separation, and U ~ the H standard deviation. While component separation is thus sharply limited, a range of useful application exists. Illustrative results are given for different types of systems. The paper describes how the analysis is organized, and outlines important algorithms.
Introductiom Potentiometric titration of a solution with OH- measures the quantity of dissociated protons as a function of pH. The shape of the curve reflects potentials and concentrations associated with the acids present in solution. If one views titration as scanning the p H spectrum, the pK values can be loosely regarded as absorption peaks. The question that motivated this work was whether it is possible to rcsolve the peaks in an unknown solution. More precisely, the question is: what are the possibilities and limitations associated with this problem? Components are distinguished here by curve fitting. In this respect the method is like that applied by Tanfordl to protein solutions. The mathematical treatment, too, is similar to Tanford’s, except for molecular charge effects that must be included for polyelectrolytes. The operation here, however, is geared entirely to the computer, and it proceeds de riovo with information inherent in the laboratory data. Titration points are fitted to a one-component model, a two-component model, and so on; and this is carried to the point where further resolution becomes meaningless. After EjUCh an analysis, one may postulate 0022-3654/79/20831365$01.OO/O
actual species in the solution, consistent with information developed by the computer. In this sense the treatment is preliminary. A study like Tanford’s, which is based in part on advance knowledge of the system, could logically follow the present type of analysis. There is a large body of work using curve fitting, often called nonlinear regression analysis, to evaluate stability constants of acids and complex ions from potentiometric measurements. Sillen and co-workers in 19622-5developed a least-squares program called LEGATROP (using Algol coding) for this kind of analysis. Unwin, Beimer, and Fernando6 produced a Fortran program for a similar purpose in 1967. Baes and Mesmer, in their book on the hydrolysis of cations? describe extensive use of the method. More recently, several groups have used least-squares fitting of the titration curve as a basis for chemical analysis. Ingman, Johansson, Johansson, and Karlsson8 used curve fitting to determine two monoprotic acids in solution, where the pK separation was in one case only 0.2 units. Barry and Meitesg applied the method to dilute solutions, showing that the equivalence point could be determined when there was no discernable inflection that would permit 0 1979 American Chemical Society
