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NICHOLS MEDAL AWARD In recognition of his work on catalysis, Hugh S. Taylor, have been judged of outstanding merit. David B. Jones Research Professor of Chemistry a t Princeton been made to the following: University, was awarded the William H. Nichols Medal for 1928 E. B. Voorhees at the meeting of the New York Section of the AMERICAN CHEM- 1903 1905 C. L. Parsons ICAL SOCIETY on March 9, 1928. After presentation of the medal 1906 M. T. Bogert 1907 H. B. Bishop Doctor Taylor delivered the address which is given below. 1908 W. H. Walker The Nichols Medal was founded in 1902 through the gift of 1908 W. A. Noyes and H. C. P. Weber 1909 L. H. Baekeland William H. Nichols and is awarded annually by the New York 1911 M. A. Rosanoff and C. W. Easley Section to that investigator whose contribution in any publication 1912 Charles James under the auspices of the AMERICANCHEMICAL SOCIETYshall 1914 Moses Gomberg
Previous awards have 1915 1916 1918 1920 1921 1923 1924 1925 1926 1927
Irving Langmuir C. S. Hudson T. B. Johnson Irving Langmuir G. N. Lewis Thomas Midgley, Jr Charles A. Kraus E. C. Franklin Samuel C. Lind Roger Adams
Catalysis as an Inspiration of Fundamental Research Hugh S t o t t Taylor PRINCETON UNIVZRSITY, PRIHCETOX, N. J.
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H E award of the Nichols Medal for 1928 serves once more to emphasize the importance of the study of catalysis not only in the development of chemical industry, but also in the realm of fundamental chemical science. For, apart from the manifold contributions to industrial chemical progress which have been secured through the application of the catalytic agent, there exists also a very definite contribution to the general problem of mechanism in chemical reactions that has been and is being achieved by study of the catalyst. To the recipient the award presents a n opportunity to discharge a threefold obligation incurred in the achievement of the honor now paid t o him-a debt t o Princeton University, to colleagues and graduate students who have collaborated in the work, and finally to chemical industry in suggesting the scientific problems that needed solution. No university could have more freely and unquestioningly supported a prolonged series of researches. Associated in this work is a long line of graduate students, all of whom it is not possible to name. The technical skill of my former colleague Doctor Marshall, and latterly of Doctor Kistiakowsky, has made possible the continuous translation of ideas into actual experimental accomplishment. A third obligation remains-and that to industry for the suggestion of fundamental problems. During the war years, in England, it was possible only to realize how very lacking in basic fundamental research the practice of catalysis was. Some of this research it has been possible to initiate since that time. A fruitful contact with E. I. du Pont de Nemours & Company has served to emphasize the need of fundamental studies over a wider field than first was realized. Much of the Princeton work, especially in the field of inhibition or negative catalysis and latterly with oxide catalysts, has sprung from this industrial contact. Much has been written of the advantages that accrue to industry from the promotion of fundamental science. In the field of catalysis it is possible to show how much fundamental science can reap of advantage from contact with industry. Against that as a background what follows may be examined. C o n t a c t Catalysis
In the field of contact catalysis industry had already ascertained empirically, prior to the initiation of the Princeton studies, a number of valuable principles of the catalytic art, which lacked, however, any extended scientific basis. Industry had learned of the importance of catalyst preparation in the determination
of catalytic activity. The problem of catalyst poisons, highly detrimental to yield even when present in minimal amounts, was already well known from the industrial development of contact sulfuric acid, the hardening of fats, and the synthetic-ammonia process. This last enterprise had also served to indicate the importance which promoter action played in the determination of catalyst activity, and the rules there observed had led to a study of promoters in other contact catalytic processes. Furthermore, the empirical studies undertaken industrially served only to heighten the specificity displayed by contact agents in a variety of reactions and gave color to the view, even now held by many skilled in the catalytic field, that the problems of contact catalysis could most satisfactorily be solved by the methods of trial and error, and that there was little room for scientific judgment and forecast as to the most suitable catalyst for a particular operation. How little of basic theory there was t o guide one in such matters is very evident from a perusal of the pertinent portions of the first edition of “Catalysis in Theory and Practise.” In the eight years (1918-1926) that elapsed between the first and second editions of this book it was necessary to expand by fourfold the space devoted to theory. It was possible in the second effort a t least to outline the basic theory which underlies these characteristics of contact catalysis, methods of preparation, poisons, promoters, and specificity. It will be possible here only t o summarize the point of view thus developed. In the development the Princeton work was only a unit in the structure which was being produced simultaneously in many different places, and of which mention may be made of the Fixed Nitrogen Research Laboratory at Washington, the Warrington researches of Armstrong and Hilditch, and those a t Cambridge under Rideal. The investigations a t Princeton centered upon metal catalysts. These were important catalysts of hydrogenation and they had the advantage that, since single metals only need be used in practice, a single species of atoms only was involved in the theoretical studies. It was fortunate also that we determined a t Princeton to seek a theoretical basis for catalyst behavior in the adsorption characteristics of these metals. Subsequent history has shown that we chose a group of catalysts for study in which the important underlying principles could be most readily and convincingly exhibited. Langmuir in 1916, in a paper which already has received the award of the Nichols Medal, had sketched the newer ideas as to the nature of the forces operative at the surfaces of solids and had
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pointed out the applicability of such ideas t o the study of contact ment of the heat liberated by a few tenths of a cubic centimeter of action. His contribution shed a new light on the century-old gas adsorbed. This represented a considerable step forward, suggestion of Faraday t h a t catalytic action was determined by but the apparatus was complicated and required at least two the forces of attraction exerted by clean surfaces upon surround- persons to operate. Quite recently we have developed a n appaing gases. Langmuir’s paper emphasized the orderly arrange- ratus of the same catalyst capacity but more readily operated and ment of atoms in the solid surface, their unsaturated nature as more compact. This permits measurements with a higher degree compared with interior atoms, and, more important still, the prob- of accuracy owing to the reduction in volume of the dead space ability that in many cases adsorption occurred in unimolecular of the apparatus. The substitution of a 25-junction thermofilms only. It was this latter concept which revolutionized the couple for the platinum resistance thermometer has simplified concept of heterogeneous reaction velocities. The work of Bo- the temperature measurement without loss of precision. denstein and Fink had suggested that these latter were primarily From measurements by Wolfenden and Kistiakowsky on t h e diffusion velocities. On Langmuir’s view they became the rates ionization potentials of hydrogen and nitrogen on the metals of chemical reactions. copper, nickel, and iron, we were led t o conclude that these eleThe work on adsorption a t Princeton was guided in its earliest ments were present on the surface of the metals in an activated stages by the ideas which Langmuir state, probably as atoms. The ionizahad stressed. It became evident, howtion potentials varied definitely from ever, that the facts of contact catalysis those of the molecular species. Fryling in many cases called for a n amplification therefore sought to establish, by a study of this treatment. The earliest work of the heats of adsorption of hydrogen at Princeton abundantly demonstrated on promoted nickel catalysts, the presthe parallelism between a d s o r p t i v e ence of a n active species and saw, i n capacity and catalytic activity-that a n initial increase in the curve of heat is, between quantity of surface and of adsorption plotted against volume quantity of reaction at such surfaces. adsorbed, experimental justification for A more penetrating analysis revealed, the assumption that the hydrogen first however, that the sensitivity of catalysts adsorbed on the active spots of t h e to heat treatment, t o poisons, and to catalyst underwent an endothermic acpromoters could only be fully explained tivation, probably a dissociation into in a varying quality of the catalyst atoms. This initial increase we have atoms in the surface. It was shown, more carefully investigated with the in a variety of experiments, that the m o r e r e f i n e d apparatus. We have p a r a l l e l i s m between adsorption and shown that it is a function of t h e catalytic activity was not an exact catalyst mass, since we can destroy i t proportionality. The work of Burns by poisoning the catalyst or by heatand of Pease (first a t Princeton and treating an active sample (Kistiakowsky subsequently with his students a t Virand Flosdorf). While, as we have alginia) showed that the effect of heat ready pointed out, there are theoretical treatment and poisons was far more difficulties in the way of unqualified acpronounced on catalytic activity than ceptance of these results, nevertheless Hugh S. Taylor on adsorption. Gauger and Russell they are now so numerous’ that we showed that in the use of supports and acceDt them as confirmation of our view promoters for nickel the catalytic action that‘at the most active centers of the and adsorptions indicated a qualitative improvement of surface catalyst a very pronounced endothermic process of activation rather than a quantitative extension of surface. All these phe- takes place. nomena became explicable if one turned from the “elementary While such studies were in progress, industrial catalysis took spaces” of Langmuir t o a composite surface upon which there were another forward step. To chemical industry the catalytic synareas of varying activity. Upon the most active spots only were thesis of methanol was important on account of the threat of the difficult reactions achieved. These were profoundly sensitive annihilation t o which the wood-distillation industry was subjected. t o poisons, heat treatment of the catalyst, and promoter action. It served to intensify a feeling of uneasiness on the part of wellThere were, however, other reactions in which the bulk of the established enterprises that they too might be among the next surface atoms were active. Such reactions would be relatively victims. There has been a very noticeable increase of respect by insensitive t o the nature of the surface or the presence of foreign industry for the catalytic agent since the first tank steamer constituents in the reaction stream unless such constituents were sailed into New York harbor with its cargo of methanol. extremely strongly and preferentially adsorbed by the contact To the student of theoretical catalysis, also, the synthesis of agent. methanol was of first significance. It represented the 6rst These conclusions led t o a new phase in the study of the catalyst. major use, as hydrogenation catalysts, of the so-called irreducible Means were sought to establish by direct physical measurements metallic oxides. Hitherto such catalytic hydrogenations had the existence of areas of varying activity and also t o ascertain the been confined to the well-known hydrogenation metals of the nature of the changes induced in the reacting gas by its asso- platinum group, the iron group, and copper. The new result, ciation with the catalyst mass. The former study has led t o however, might well have been anticipated, since there was a the development of methods for measuring the heat of adsorp- steadily growing mass of literature in which the pronounced detion of minute amounts of gases on catalytic agents. The earlier hydrogenation activity of such oxide catalysts had been estabwork on adsorption and poisons had shown the necessity of thus lished, and the reverse process of hydrogenation became a thermoconcentrating attention on the gases adsorbed at minute partial dynamic necessity. We were hardly prepared t o find, neverpressures. In the first apparatus (Beebe) we were content with a theless, upon examination of such catalysts by the methods t h a t measurement of the heat liberated upon the adsorption of a few had shown good service with the metals, that these oxides excubic centimeters of gas, and a Beckmann thermometer sufficed hibited adsorption characteristics t o a n even more pronounteed for the temperature measurement. Next we employed (Kistia1 See Garner and McKie, J . Chcm. SOC.(London), 2457 (1927), for kowsky) a platinumresistancethermometer t o permit the measure- similar results with oxygen on charcoal.
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degree than did the metals. That this is so, however, is evident from Table I taken from one of our recent publications.2 It will be noted that the adsorption of hydrogen on a zinc oxide-chromium oxide catalyst is higher a t 100" C. and 1 mm. pressure than the adsorption of our best nickel catalyst a t 0' C. and 760 mm. Table I--Adsorptions per 100 grams of Catalyst CATALYST H2 ADSORBED TEMPERATUREPRESSURE cc. 0 c. Mm. Reduced Cu 13.4 110 i60 Reduced Cu 45 0 760 Reduced S i 130 0 760 ZnO-CrrOa 184 100 1 ZnO 50 0 20
I t is well to emphasize these findings, since there has recently been a marked tendency to discount work of this nature as an auxiliary method of approach to the discovery of suitable industrial catalysts. It is safe to say that, had such results been available t o and appreciated by the chemical directors of industrial corporations several years ago, it would have been possible to lay down with precision the conditions under which the industrial synthesis of methanol could be achieved. It would have been possible to state that zinc oxide would be a good catalyst but that mixtures of zinc and chromium oxides would be far superior. It could have been stated that these catalysts would be found superior t o a metal catalyst such as copper, that they would be relatively less sensitive to such constituents of industrial gases as carbon dioxide, oxygen, and water vapor. It could have been forecast that these catalysts would begin to function well in the temperature range of 300' to 400' C., so that, with the aid of well-known equilibrium calculations, the maximum yields attainable with a given gas mixture could have been deduced before experiment was undertaken. The adsorption characteristics of these oxides parallel those of the metals. There is rapid saturation of the surface a t low pressures and small change as the pressure is raised. This behavior is characteristic of adsorptions involving high heats of adsorption. Mr. Flosdorf has now made preliminary experimental measurements of the heat of adsorption of hydrogen on a zinc oxide-chromium oxide catalyst. The results confirm our anticipations since values of 40,000 calories per mol of hydrogen adsorbed a t low partial pressures have been obtained. It is pertinent again to emphasize the contrast between such values and the heat of liquefaction. In every case that we have so far studied, the heat of adsorption of reactants on a catalyst has involved the liberation of energy quantities far in excess of liquefaction energies. This points t o a profound modification in the make-up of the molecule by its association with the surface. Chemical Reactions Induced by Excited Mercury The assumption that, in catalytic hydrogenation processes, the hydrogen was present in the catalyst surface in the atomic condition led to our studies of the properties of atomic hydrogen in hydrogenation processes. The method developed by Cario and Franck for producing atomic hydrogen permitted such a study a t room temperatures under simple experimental conditions. It was necessary simply to allow the resonance radiation = 2536.7 A. from a cooled mercury arc t o fall upon a quartz reaction system containing mercury vapor, hydrogen, and the gas with which it was desired to cause atomic hydrogen to react. T h e energy of the resonance radiation (112,000 calories) was absorbed by the mercury vapor to yield an excited atom Hg', which was communicated to the hydrogen by collision causing a dissociation into atoms, Hg light (A = 2536.7 A) = Hg' Hg' HP = Hg 2H Atomic hydrogen so produced is reactive with a variety of substances. Among the more noteworthy reactions is that with
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Taylor and Kistiakowsky, J . A m . Chcm. Soc., 49, 2465 (1927).
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oxygen to yield hydrogen peroside and with carbon monoxide to yield formaldehyde. It is worth recording in regard to the latter reaction that formaldehyde is not the only major product. Investigations of this type conducted in the I. G. laboratories a t Oppau have shown that glyoxal is also a major reaction product. According t o Doctor Frankenburger, this must result from a chain mechanism of the type H CO = HCO HCO Hz = HCHO H HCHO HCO = (HC0)z H From considerations based upon relative yields and collision frequencies he concludes that reaction (3) is much more readily achieved than reaction (2). The actual calculation indicates that only 1/5o0 of the collisions in (2) are fruitful for each fruitful collision in (3). The German investigations have confirmed the results obtained in Princeton by Doctor Marshall, which showed that the reactions of atomic hydrogen with oxygen and carbon monoxide were chain processes, although the chains were short. The activity of excited mercury is not confined to the dissociation of hydrogen. The recent work of Bates in Princeton showed definitely that a wide variety of decomposition processes could be produced by means of excited mercury. Among other compounds, ethylene, hexane, formic acid, alcohols, esters, amines, and ammonia were all broken down a t room temperatures. Such a method of producing chemical reactions is of great utility, since it facilitates a study of the stages in the total process unhampered by factors which become controlling when high temperatures are required to produce decomposition. This may be illustrated by results obtained by Bates with ammonia and by Elgin with hydrazine. By means of a flow method Bates showed that the initial products from the decomposition of ammonia by excited mercury contained much more hydrogen than would be obtained in a stoichiometric decomposition. This suggested that the decomposition might occur through hydrazine as an intermediate stage, Hg' NH3 = Hg NHI H NH.NHI = NzH4 H Meanwhile, the researches of Dickinson and Mitchell had shown that the mercury-sensitized decomposition of ammonia was markedly inhibited by hydrogen, while nitrogen and argon were without effect. Since it was difficult to push further our understanding of the mechanism by a study of ammonia alone, we undertook a similar investigation with hydrazine. This work is now nearing completion and has proved to be extremely illuminating. Mr. Elgin has shown that the sensitized decomposition of hydrazine occurs a t least twenty times more rapidly than the corresponding reaction with ammonia. Indeed, the decomposition of hydrazine is, thus far, the most rapid reaction we have studied with excited mercury. It occurs a t least twice as rapidly as the combination of hydrogen and oxygen under the same conditions of mercury concentration and illumination with resonance radiation. It is apparent, therefore, that the decomposition is a chain reaction with chains a t least twice as long as those in the formation of hydrogen peroxide. This rapid decomposition, moreover, does not yield the elementary constituents. On the contrary, a t the close of the rapid reaction we have demonstrated that the products are ammonia, nitrogen, and hydrogen in the amounts to be expected from a decomposition in accordance with the equation 2NzH4 = 2NH3 Np Hz We have separated and analyzed more than 90 per cent of the ammonia to be expected on this basis. It is apparent, therefore, that hydrazine decomposition proceeds through ammonia. The kinetics of the process indicate, however, that it is not bimolecular since the rate is practically constant until the reaction according to the above equation is substantially complete. Then follows a slow decomposition of ammonia.
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Further investigation showed that the rate of hydrazine decomposition is independent of nitrogen, ammonia, and hydrogen concentrations, even when these are present in great excess. This independence of hydrogen concentration, in sharp contrast to the case of ammonia, is a most remarkable result, since i t is already known that collisions between excited mercury and hydrogen molecules are completely inelastic. This means, therefore, that the energy of those mercury atoms which collide with hydrogen is still in some manner available for decomposition of hydrazine. A mechanism such as is represented by the equations Hg’ NzH4 = Hg f NzH3 H NzHs f NzH4 = 2NH3 f Nz H , H NZH4 = NZH3 f HZ would account for the products of the sensitized decomposition, the speed with which it occurs, the independence of the hydrogen concentration, and the chain mechanism of the reaction. Whether it corresponds to reality further experiment must show. The mechanism Hg’ NzH4 = Hg NzHz Hz NzHz NzH4 = 2”s Nz would account for the products formed but not for a chain mechanism. Also, hydrogen would be expected to retard the rate of decomposition in the sensitized reaction. It is of interest to record that in the straight photochemical decomposition of hydrazine the products are also ammonia, nitrogen, and hydrogen, with simultaneous further photo-decomposition of the ammonia formed, though a t a much slower rate. The thermal decomposition of hydrazine a t 250” C. in a quartz vessel yields almost exclusively ammonia and nitrogen. This would suggest a trimolecular reaction 3NzH4 = 4NH3 f Nz We are making kinetic studies of this reaction. Ethylene, when subjected t o the action of excited mercury, undergoes polymerization t o yield a liquid of high vapor pressure and of the empirical formula C,Hz,, since there remains little residual gas and this contains hydrogen, methane, and some higher hydrocarbons. The presence of hydrogen in this case enormously increases the rate of disappearance of ethylene. It acts approximately proportionally to its concentration. Experiment shows that this influence of hydrogen is not due mainly t o the production of ethane. I n a given experiment, hydrogen equivalent t o 30 per cent of the initial ethylene disappeared during the reaction. Between the temperatures of solid carbon dioxide and liquid air the condensate from the reaction products, which we may call ethane, amounted to 12 per cent of the initial ethylene. Between room temperature and -78’ C., a condensate of the products equal t o 16 per cent of the initial ethylene was formed. If this were C, hydrocarbons, it would mean that 32 per cent of the ethylene disappeared this way. The residual 56 per cent ethylene was evidently transformed to liquid products mainly unsaturated but possibly in part saturated. The complete analysis of this complex yield will require a n elaborate technic. For the moment it must suffice to record that all these reactions are enormously more rapid when photosensitized by mercury than as straight photo-reactions. It is of interest also t o note that, thus far, the polymerization of ethylene is the only photosensitized reaction that we have secured with a new technic using excited cadmium a t 250” C. as the photosensitizer. In this case the resonance radiation is at X = 3262 A., of which the corresponding energy quantity is 87,000 calories, or approximately 14,000 calories less than the dissociation energy of hydrogen and some 25,000 calories less than that of excited mercury.
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Inhibition of Chemical Reactions The Princeton studies in catalysis have also extended to a scientific investigation of the retardation of chemical reactions by small amounts of added materials-a field quite generally
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known as negative catalysis but which may be more properly described as inhibition. Originally a purely academic problem studied by Bigelow and by Young in the oxidation of solutions of sodium sulfite, it has recently acquired an extended industrial importance since it has been realized that autoxidation processes are involved in many cases of deterioration. The development of rancidity in oils, the deterioration of textiles and fibers and of rubber, the fading of dyestuffs, the discoloration of unsaturated organic compounds, possibly the combustion of gasoline, are examples of reactions for the prevention of which the use of inhibitors has been invoked. For a period of years it has been customary to adopt the view of Moureu and Dufraisse in this matter and “explain” the action of inhibitors by a sequence of reactions, of which the following may be cited as typical for an autoxidizable substance A with inhibitor B:
The problem of inhibition is really more interesting than such ideas would indicate. Doctor BBckstrom submitted to experimental test in Princeton a theory of inhibition due to Christiansen. According to this theory reactions which show inhibition are chain reactions; that is to say, they are processes in which the energy of the reaction products is transferable to molecules of reactant, thus activating them. I n such chain processes an initial reaction between a single pair of molecules may suffice to promote a sequence of similar reactions many thousands in number. When such chain reactions are photosensitive, the chain mechanism is readily demonstrable. It is only necessary to measure the number of quanta of activating energy and the number of molecules thus brought to reaction. Biickstrom reported recently the outcome of such measurements for the oxidation of aldehydes and of aqueous solutions of sulfites. He showed that in these typical examples of inhibited reactions as many as 10,000 t o 50,000 molecules underwent reaction for each quantum of monochromatic light energy absorbed. Christiansen’s theory was thus emphatically confirmed. It is impossible here to develop in detail the full consequences of this theory of inhibition. This has been done comprehensively by Backstrom. He traces out the connection between the chain reaction theory and the phenomenon of chemiluminescence shown by autoxidizable substances. The oxidation of phosphorus is a familiar example of chemiluminescent reaction shown by BBckstrom to be a chain reaction. His work also indicates that chain reactions, and therefore those which show inhibition must also be photosensitive, and the photo-reactions show many molecules reacting per light quantum absorbed. The autoxidation reactions show, moreover, the phenomenon of photosensitization in such a degree that this may be regarded as characteristic of such reactions. As Christiansen pointed out, the inhibitor acts by breaking the sequence or chain of reactions. The theory as developed by Backstrom leads t o an important conclusion as to the mechanism of the inhibition. This, in the case of autoxidation reactions, may involve a n oxidation of the inhibitor. It may, however, involve a variety of other reactions, such as condensation, polymerization, or the like. It will, in general, be characteristic of these chain-breaking reactions that they will be “photochemical” in the sense that one of the reacting constituents of these final reactions shall be activated by one of the energyrich reaction products, and that this activation will be similar in magnitude to that produced by light absorption. It is, however, on the quantitative side that the chain-reaction theory has proved decisive. If a n inhibitor of oxidation acts by breaking a chain which is as many as 50,000 units in length, it follows that the principal reaction can be cut down 50,000 fold for unit oxidation of inhibitor. We have sought t o study this a t Princeton, making use of sodium sulfite oxidation and several alcohols as inhibitors. Mr. Alyea has succeeded in showing that
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with three inhibitors-isopropyl, isobutyl, and benzyl alcoholin a given concentration of sodium sulfite solution, the amount of alcohol oxidized per unit time is constant over a wide range in concentration of inhibitor, this range varying with the inhibitor chosen; the number of molecules of inhibitor oxidized, however, in unit time remains identical from case to case. The experiments also show that, over the range of inhibitor concentrations studied, the amount of sulfite oxidized is inversely proportional to the inhibitor concentration. This means that the inhibitor does not influence the number of reaction chains started and that each chain started is ended by an inhibitor molecule. The amount of inhibitor oxidized is also significant. It is approximately one fifty-thousandth of the amount of the sulfite which would have been oxidized under the given conditions had the inhibitor not been present. This has demanded a special technic of measurement of such slight amounts of oxidation. The examples chosen are those for which sensitive quantitative colorimetric methods of estimating the oxidation product could be developed. This has proved to be possible in the case of acetone, methylethylketone, and benzaldehyde, the three oxidation products of the several alcohols studied. The data obtained are summarized in Table 11.
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These results are obvious on the chain-reaction theory. The constant amount of oxidized inhibitor means that substantially every chain is broken by a n alcohol molecule being oxidized once a certain alcohol concentration is exceeded. The minute amount of alcohol oxidized is also understandable on the chain theory. The varying efficiency of the inhibitors, as evidenced by the varying lower limits of concentration a t which substantially complete inhibition is secured, is however a matter which calls for more than passing attention. It is a problem full of significance in the general question of reaction mechanism to ascertain why the destruction of reaction chains in equivalent alcohol concentrations occurs thirty-seven times more frequently with benzyl alcohol than with secondary isobutyl alcohol. It is a matter, too, of high scientific interest to learn by what mechanism the energy-rich reaction products of the sulfite oxidation transfer that energy to unoxidized sulfite molecules even in aqueous solutions less than 1 molar in concentration, in which, therefore, a t least fifty-five collisions with water molecules occur for every collision with a sulfite molecule. Conclusion
There are those who imagine that industrial problems are lacking in thrills for the pure scientist. They surely cannot have Table 11-Action of Alcohols as Inhibitors of Sodium Sulfite realized the inspiration and stimulus to fundamental research Oxidation which achievements in the field of industrial catalysis have so RATIO INHIBITOR abundantly produced. Over the fireplace in the new chemical MOLS0x1DIZED t0 laboratories now under construction in Princeton there will be CONCN. INCREASERELATIVE ALCOHOLSULFITE MOLS RANCG OF IN ALCO- INHIBITION 0x1NORMALLY inscribed the motto “Felix qui potuit rerum cognoscere causas.’’ POWER OF DIZED A OXIDIZED* HOL ALcoiroL It is that happiness in learning the cause of things which has ALCOHOL C V - K * l o % C O N C N . ALCOHOL 15% 15% been the chief joy of these studies and which has brought in its Mols Mols/hour Isopropyl 0 , 0 2 5 to 2 , 5 100-fold 3 0.000046 1:54,000 train the additional joy of the appreciation of which this occasion sec-Isobutyl 0 . 1 5 t o 1 . 8 12-fold 1 0.000049 1:51,000 is a testimony. Benzyl 0.005 to 0 . 1 7 34-fold 37 0.000049 1:51,000
NOTES AND CORRESPONDENCE Tin Plate and the Electrochemical Series Editor of Industrial and Engineering Chemistry: I n a recent paper Kohman and Sanbornl have shown that under certain conditions in canned fruit juices the electrochemical relations usually assigned to the tin and iron comprising tin plate are reversed, the tin becoming anodic t o the iron. This confirms the results of experiments carried out in the writers’ laboratory in the winter of 1924 and 1925. Like Kohman and Sanborn, the writers cannot subscribe to the views recently published on this subject by Mantel1 and Lincoln,2 who have stated that, in fruit juices in general, tin continues in a cathodic relation t o iron, thereby accelerating the corrosion of iron with which it is in electrical contact. The writers have demonstrated that immediately after contact with many fruit juices or a water solution of citric and malic acids tin and iron exhibit their normal electrochemical relations; i. e., iron is the anodic metal. However, this condition is quickly reversed and the iron ceases to be corroded a t an appreciable rate. This reversal of the polarity in the tin-iron cell under suitable conditions is the direct result of the large difference in the hydrogen overvoltage of the two metals-tin = 0.53 volt3 and iron = 0.175 v o l t 4 The results of the writers’ investigations are now being prepared for publication. I n d . Eng. Chem., 20, 76 (1928). (1926); Zron Age, 119, 843 (1927); Can. Chem. Met., 11, 29 (1927); A m . Metal. Markef Monthly Rev., 33, 242 (1926). a Caspari, Z . phys. Chem., 30, 89 (1899). 4 Thiel and Breuning, Z . anorg. Chem., 83, 329 (1913). 1
* Canning Age, 7, 847
Although the observations of Kohman and Sanborn confirm those made in this laboratory a t an earlier date, we cannot agree with these authors in their attempt t o apply their results to the commercial aspects of corrosion in the tin container. As far as the canner is concerned, one of the most serious results of corrosion in the tin can is the perforation of the tin plate. Kohman and Sanborn have stated that perforations develop at points where the iron base is exposed by imperfections or fractures in the tin coating. It has been conclusively demonstrated both by experiment and commercial practice that the rate at which tin plate is perforated decreases with increase in the weight of tin coating. I n attempting to explain this fact on the basis of their results, Kohman and Sanborn assume that increasing the thickness of tin coating decreases the total area of iron base relative to the area of the tin coating exposed t o the contents of the can, and state: “Increasing the tin coating decreases the area of t h e cathodic iron relative t o the anodic tin and, in accordance with the electrochemical theory, corrosion of the iron is reduced.” On the basis of this statement one would expect that any increase in the area of iron base relative to that of the tin coating exposed in the can should bring about an increase in the rate a t which a can is perforated. This view is not in harmony with results previously published by the same authors,6 in which it was shown that in enameled cans free from tin coating perforations develop a t a much slower rate than in enameled cans carrying a normal weight of tin coating. It appears that Kohman and Sanborn have fallen into the 5
Kohman and Sanborn, Ind. Eng. Chcm., 19, 514 (1927).
