VOL.6, No. 12
PRINCETON'S NEWCHEMICAL LABORATORY
PRINCETON'S NEW CHEMICAL LABORATORY
The Dedication Distinguished scientists of Europe and of America met a t Princeton, New Jersey, on September 26, 1929, to attend the dedication of the University's new Chemical Laboratory, and to be present a t the international conference on catalysis and the mechanism of chemical reactions which was held on September 27th and 28th. A t 12.30 P.M. on Thursday, September ZGth, the academic procession, its numbers swelled by the presence of the representatives of forty colleges and universities of this country, of seven learned societies and foundations, and of six foreign universities and institutes, filedkto the auditorium of the new Laboratory for the exercises. Following the singing of "America," Mr. Charles Zeller Klauder, the architect, presented the symbolic key of the building to President John Grier Hibhen, and addressed him as follows: MR. PRESIDENT:As early as 1916 we began our studies for the design of the Chemistry Laboratory. Many solutions were suggested and considered. The heads of the department were a t all times most helpful. We were quite surprised to discover haw much time and effort were devoted to the study of the best plan by the members of the staff. Indeed, I doubt whether any architect could alone design a successful chemistry laboratory because he would be without knowledge of the countless details of a d a n t necessary to the teachina of such a special science as chemistry: nor would he know exactly how the building was to function in the univ%sity life and curriculum. Many laboratories of recent construction were visited by the members of the faculty and ourselves during the course of the making of these designs for the building. I t was discovered that each of those buildings was based on some salient idea. But each differed from others in the choice of idea favored. In this building the laboratories were made to surround the stockrooms so that deliveries could be made to the different outlying rooms witb the least difficulty. By concentrating the stockrooms in the plan, that is, one above the other as they are arranged here, instead of dispersing them.on each floor, unnecessary duplication and expense are believed to have been avoided. A flat roof parapeted type of Tudor or Collegiate Gothic architecture was adopted in order t o avoid not only the waste space resulting from the use of steep pitched roofs, but the expense entailed in constructing such a roof itself. All of this made it necessary for us t o study the architectural masses of the building witb areat care, for the result we knew should be a composition in mass without recourse t o steep roofs for effect. I trust the result is satisfactory, and I take pleasure in banding you this key with the hope that the building will in every respect function as intended.
In opening his speech of acceptance President Hibhen paid tribute to Mr. Klauder's skill and said that in many ways the Chemical Laboratory was the crowning effort of his work on the Princeton campus since the designing of the building presented many unusual problems not encountered in other structures.
He revealed that the University was $n the point of erecting a smaller laboratory in 1915 which was to be the gift of Mr. Henry Clay Frick. Mr. Prick went so far, he declared, as to purchase for the University the plot of ground on which the new building stands, but the advent of the World War made it inadvisable to build at that time. He said that he felt now that the delay had been for the best, since the present building was more adequate in proportion and arrangement. In referring to the key which Mr. Klauder had handed to him, President Hibben said that he preferred to recognize it as the key to the door of knowledge, although he realized that there was no portal through which one might pass directly into knowledge. President Hibben said that the Laboratory would not have been justified if the University had not had a t its disposal the recently completed $3,000,000 fund for research in pure science and if i t did not have men capable of excellent research work. He declared that since he believed that the future had more discoveries in store than the past had had, he hoped that out of the new Laboratory might come discoveries which would be important to the world of chemistry and physics.
A f t e r P r e s i d e n t H i b b e n had concluded, Professor Hugh Stott T a y l o r , C h a i r m a n of the D e p a r t m e n t of C h e m i s t r y , delivered an address, w h i c h is as follows: This is indeed a happy and historic day in the development of chemistry a t Princeton. On behalf of the members of the Department of Chemistry I wish to express our indebtedness to you, President Hibhen, and to the Board of Trustees of the University for the courage and generosity with which you have met the demands a t Princeton for a laboratory so splendidly constructed and equipped as this building which you now turn over t o our care. Through a long period of years we have waited hopefully for this day and our trust in your determination to do everything that was possible for our welfare has been handsomely justified. We are proud of this fulfilment of our dreams and wish to thank those who have coooerated with us so whale-heartedly in the effort. To the architects we owe a design a t once architecturally handsome and yet eminently practical for the purposes to which i t is t o be put. The coiiperating engineers have ensured that the structure is efficiently equipped with heat, light, power, ventilation, plumbing, stoneware service, and all the other details that a modem chemical laboratory must possess. The designs of architect and engineer have been translated into the realities that we see around us by a varied group of organizations, too numerous t o detail, but t o which we wish t o express our heartiest thanks for their ever-evident effort not only to do the job but to do the job in the best possible manner. Those of us who have been most intimately associated with the work know that in every instance the best in thought and effort has been offered for our better sstisfaction. Professor McCay and I wish on this occasion publicly t o express our appreciation to our absent colleague, Professor Lauder W. Jones, for his large share of the labors of the departmental committee responsible forth" work. Many of the details of design in the building are the result of his rich store of experiapce in the construction of laboratories. Lareelv - - owina.t o the unremittina labor and care of our Curator. Mr. W B. Foulk, these details have been achieved and to him also we owe an outstanding contribution t o the oroblems of chemical laboratory stock distribution, organization, and control. We owe a special debt of gratitude to the numerous benefactors, research foundations, public spirited corporations, friends and alumni of Princeton who, by their generous contributions, have enabled the University t o open these laboratories to a large staff of teachers, research men, and students who may carry out their tasks with adequate equipment and an endowment which meets the present needs generously. We wish t o thank those who have come t o us today from far and near t o share with us our happiness. We are especially honored by our foreign guests, and are proud to have with us so distinguished a company of honorary alumni. To the representatives of the universities, colleges, learned societies, and research foundations we tender our appreciation of their presence. We trust they may take back with them pleasurable memories of their visit. The successive laboratories a t Princeton have covered the whale epoch of modern chemistry. From Old Nassau, the lectures of John Maclean, two of which we have reprinted and distributed among you today, voiced the dissatisfaction of the late eighteenth century chemist with the theory of phlogiston and his belief in the new principles of the science which the quantitative data of Dalton and Lavoisier made possible. From 1873 to 1891, chemistry a t Princeton, in the old John C. Green School of Science, was largely descriptive and analytical. Outside, in the Old World, organic chemistry was in its full flood of development, but contacts with Princeton were few and the processes of change were but slow. ~
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VOL.6, No. 12
PRINCETON'S NEW C ~ M I C ALABORATORY L
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In 1891, thc chcmical laboratory on Nassau Street, @vised and equipped through the exertions d Professor Henry Bedinger Cornwall, was opened for use. In thislaboratory the old era passed and the great change began. Young enthusiasts, fresh from their
chemical education. The curve of progress has been ever upward; some of us feel with pride that it is auto-accelerative in its nature and wonder to what pace it will attain. Certain it is that, in the recent yean, the growth has been abnormally rapid and has rendered imperative the building we dedicate today. During the life time of the old laboratory the science of physical chemistry has had its rise t o full estate. There are now abundant evidences that in the new fields to he conquered chemistry must draw yet more largely from her sister sciences of physics and mathematics. Ways have been devised to ensure close cooperation between the sciences, resulting in the drawing of ever increasing numbers of students to our graduate schools from all parts of the world. We commend especially to the parentsand guardians of our Princeton undergraduates a serious considerationof the rich opportunities for scientific training which Princeton now offers in contrast with earlier decades and we bespeak their counsel and encouragement to their sons seriously to consider theopportunities to which they are heir. In return for their labors we offer them a life in science rich in its satisfactions, full, scholarly, and enduring. "Non est mortuus p i scienliam uivifica~it."
At the close of Professor Taylor's address Dean Augustus Trowbridge of the Graduate School presented the candidates for the honorary degree of Doctor of Science as follows:
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JOURNAL OP CHEMICAL EDUCATION
DECEMBER, 1929
IRVING LANGMUIR,' President of the American Chemical Society, claimed as a distinguished colleague hy physicist and chemist alike and recipient of prizes and honors from national and foreign societies in both sciences. He completed his studies for the doctorate a t the University of Gdttingen in 1906 and returned to this country as instructor in chemistry a t Stevens Institute. In 1909 he was called to take a leading part in carrying out a far-sighted policy of fostering research in pure science adopted by the General Electric Company. In the laboratory of this great industrial corporation Langmuir has for 20 years attacked fundamental problems with the freedom af an academician yet with all the powerful resources of the industrial engineer. Langmuir's is the accepted concept of adsorption and the orientation of molecules a t surfaces; his studies have furnished us a mechanism of gas reactions a t the surface of the metal tungsten, universally used in electric illumination, long distance telephony, and radio. A brilliant investigator in command of twls worthy of his skill, Langmuir has made important contributions t o our knowledge of molecular and atomic phenomena. MAX BOD EN STEIN,^ Professor of Physical Chemistry in the University of Berlin and Director of the Institute which has l o w been preCminent in this field in Germany and has attracted students of the science from all parts of the world. As research student with Victor Meyer and later while privatdozent with Ostwald, Badenstein, early in his noteworthy career, began the series of classical researches on the velocity of chemical transformations with which he has enriched the subject of readion kinetics. To Bodenstein is due the concept of chain reactions which has heen of fundamental importance in the explanation of chemical readions in general. To him also is due the discovery of the r81e played by the purely chemical changes which follow on the adsorption of light by photochemical systems and this discovery has cleared a new and fruitful field of work. Bodenstein worthily maintains the high traditions of initiative and thoroughness which has characterized G m ' a n chemical research. IRVINE,~ ~ ~ N Principal and Vice Chancellor of the University of St. Sm JAMES C ~ L Q U H Photo by courtesy of I n d . & Eng. Chem. Photo by N. Perscheid, Berlin. V h o t o by Wide World Photos.
Andrews. Through his writings while professor of chemistry he won a world-wide recognition as expert on the structure and synthesis of organic compounds, notably of the sugars and of cellulose. I n the period of industrial depression following on the war the British Government secured unpartizan technical advice and aid in framing and administering reconstructive measwes. I n the department of scientific and industrial research Sir James' great executive ability, combined with the mastery of a pure science on which industries of great national economic importance are based, was early enlisted and generously devoted in the service of his counhy. PBRRIN14Nobel Prize Laureate, JEANBAPTISTE Director of the Laboratory of Physical Chemistry of the University of Paris and Director of the newly founded Institut Rothschild for Research in BioPhysics. A native of the city in which Pasteur made his first important diswvery, Perrin was early attracted to a scientific career a t the age of twentyone and secured by competition a place in the ficole Nomale Superieure. On graduation he was retained as teacher in this the highest school in France's system of public instruction. We owe to Pemn the classical determination of the magnitude of the important physical constant known as Avogadro's Number, and we owe to him also the demonstration of the applicability of the atomic concept to small particles showing the "Brownian Movement." His masterly analysis of this phenomenon has laid the foundation of a rational study of colloidal systems and thus opens the way for further and much needed work in bia-physics. His ideas on the interaction of radiation and matter, while they have not obtained general acceptance, have had a stimulating effect on research on the mechanism of chemical reactions. Perrin possesses in a marked degree the qualities of the eminent scientists of his gifted race: Photo by A. B. Lagrelius Westphal, Stockholm, and reproduced here through the wurtesy of Mr. Sederholm, managing director of Nobelstiftelsen, Stockholm.
strong individualism, daring and imagination in the interpretation of results, clarity in exposition. FREDERICK GEORGE DONNAN: Professor of ChemistryinUniversity College, London. A pupil of van't Hoff and of Ostwald, his outstanding contribution to science has heen the application of the theories of physical chemistry t o the chemistry of colloids and especially t o biological processes occurring a t cell walls. His pioneer work on equilibria of salt solutions a t membranes has guided innumerable studies of the conditions obtaining in living matter and has determined in great measure the direction which hio-ohvsical research has taken. . . In Liverpool and in London under Donnan's guidance were maintained the leading ~hvsica-chemical institutes for research in the British Commonwealth and from these . . has gone out a whole generation of scientists who are guided in the discovery and produdion of new and useful substances by the chemical philosophy of this great investigator and inspiring teacher.
President Hibben conferred the degrees upon them; Secretary V. Lansing Collins slipping the orange hoods about their shoulders. The exercises were concluded by a prayer and benediction pronounced by Dean Robert Russell Wicks of the University Chapel, and by the singing of "Old Nassau." With the completion and dedication of the new Chemical Laboratory, Princeton is providing modern housing and equipment for a chemical tradition which is one of the oldest in the country, a chair in the science having been established here in 1795. At that time a fund of a few hundred pounds was raised to purchase laboratory equipment for Dr. John Maclean, the Scotch physician, who was Princeton's first c h e m i ~ t . ~ The guests at the dedication were entepained a t luncheon at the Princeton Inn, and in the afternoon the ladies of the chemistry department gave a tea and reception in the library of the new laboratory. On the evening of the same day, in'the auditorium of the Chemical Laboratory, Professor F. G. Donnan, F. R. S. of the University of London, gave a public lecture on "The Application of Physical Chemistry to Chemical Industry with Special Reference to Catalysis." The Laboratory The building is constructed of native stone, granite, and limestone; and, as expressed by the architect, is "built around the stockroom." The laboratory has a fine appearance and is well arranged and lighted. It is so constructed that the middle floor is entered directly from the level of the street, yet all the windows of the laboratory are above ground, thus insuring abundant daylight. The auditorium seats 320 people. I t is completely equipped, and can be quickly and easily darkened for pictures or for demonstrations requiring darkness. Photo by Elliott and Fry, London. See "Some Letters hy Dr. John Maclean," by W. Foster, THISJOURNAL, 6, 2104-14 (Dec., 1929). . 6
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The library is the most attractive room inthe laboratory. It is panelled in oak, comfortably furnished for reading, and has two fireplaces over which are carved the following mottoes:
"Happy is he who hath learned the whence and wherefore of things."
"He is not dead who hath given new life to knowledge." (Quoted by R~CHARD DE BURY,Philo6iblon, Chap. 19,from the "Almagest" of Ptokmy the Mathematician, who lived about 139 A.D. The original, in Greek, has been lost.) A special librarian is in charge. In addition to ofices of faculty members, a lecture room, and a library, the new Chemical Laboratory has nine large laboratories, with windows on three sides, and thirty smaller ones, the former being for undergraduate classes and the latter for men engaged in research. There are three lecture rooms, seating from 70-100, and four recitation or quiz rooms, seating 25. The small laboratories have very little permanent apparatus in them and are so arranged that any type ,of equipment can be set up in them from time to time, in accordance with the desire of the research workers. Every room has outlets for all types oFelectric current in high and low voltages; and steam, gas, hot and cold water, and compressed air are piped to every room. Hydrogen sulfide is piped to rooms from a gasometer in the upper part of the building, which is filled from tanks containing the substance under pressure. There is an outlet in every laboratory for distilled water, which is supplied by an automatic still. The floors are largely rubberstone tile and asphalt, or "mastic," and the walls are constructed of terra cotta ashlar. The plumbing is exposed, and the waste lines are of acid-proof stoneware. The laboratories are equipped with steel desks with tops of Alberene, and are built in movable units, thus giving ready access to plumbing. There are individual down-draft hoods in the laboratories for general chemistry and qualitative analysis. The open-type hoods are fitted with Duriron steam-baths with tops of Monel metal, and each hood has a fireproof lighting fixture in the ceiling. All metal fixtures are chromium plated. The furniture and shelving are constructed of steel.
The laboratory contains a metal ware reclamation room, in which apparatus is cleaned, coated with enamel, and then baked. This room prevents much loss. There are many more important features in the laboratory, such as the electrical cleaning equipment, the charging control board, the automatic telephone, the machine shop, the glass-blowing room, and the coat room. The entire building is thoroughly ventilated; the air is washed and then preheated to about SOoF., and the temperature in the various rooms is thermostatically controlled. There is complete change of air in from three to five minutes. The cost of building and equipment was more than $1,500,000. Conference on Catalysis and the Mechanism of Chemical Reactions The following program was presented: Friday, September 27, 1929, 10.00 A.M. (1)
DR.IRVING LANGMUIR, President of the American Chemical Society: "Chemical
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Pno~~sson MAXBODENSTEIN, of the University of Berlin: "The Mechanism of
and Electrical Properties of Adsorbed Films on Tungsten." the Catalytic Oxidation of Ammonia." Friday, September 27, 1929, 2.00 P.M.
PERRIN, of the University of Paris: "Fluorescence and the Problcm (3) DR. FRANCIS of Negative Catalysis." MR. C. N. HINSHELWOOD, of Oxford University: "Trace Catalysis and Chain (4 ). E Reactions." of the Kaiser Wilhelm Institut, Berlin: "Atomic Re( 5 ) PnoaRsson M. POLANYI, actions and Luminescence in Highly Dilute Flames." Saturday, September 28, 1929, 9.30 A.M. (6) Dns. K. F. BoNHosaFER and P. HAnTEcK, of the Kaiser Wilhelm Institut: "Parahydrogen. Atomic Hydrogen and the Mechanism of Flame Reactions." and W. FRANKBNE~RGER, of the I. G. Laboratories, Oppau. (7) Dns. A. MITTASCH Germany: "The Historical Development and Theory of Ammonia Synthesis." Paper (7) is published in full immediately followiog this account of the dedication.
(8)
See page 2097.
Dns. H. MARK, H. DOASE,and W. KALBERER, of the I. G. Laboratories, Ludwigshafen, Germany: "Kinetics and Adsorption a t Contact Surfaces."
N o i c Papers (7) and (8) were presented on behalf of the authors by Paorssson Huorr
S. TAYLOR.
Abstracts of six of these papers immediately follow. LANGMUIR, Assistant Director of the General Electric ComDR. IRVING pany's Research Laboratory, discussed the behavior of oxygen on tungsten and tungsten-caesium filaments. His early work in this field had shown that oxygen molecules a t pressures of the order 0.01 to 0.001 mm., react with a tenaciously adsorbed film of oxygen, possibly atomic, on the tungsten surface. The product in this case is W03. From kinetic 0. = WOS studies it was shown that the activation energy of the reaction W = 0
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was of the order of 32,000 calories, a normal value. By a special experimental device it was found possible t o extend this study to pressures as low as 0.001 micron. The data obtained lead to the conclusion that under the given conditions no reaction between oxygen molecules and adsorbed oxygen atoms occurs a t the low pressures; that, on the contrary, what is being measured is the rate of evaporation of oxygeu atoms. The kinetic analysis leads t o a value of 7.3 volts or 164,000 calories for the activation energy of this evaporation process, a result which signifies that oxygen atoms are more strongly bound to tungsten surfaces than are oxygen atoms to one another in the oxygen molecule (6 volts > Do, < 5 volts). These results are confirmed by a study of the evaporation of electrons from tungsten filaments partially covered by oxygen in presence of caesium vapor. I t has been found that the evaporation of electrons from caesiated filaments covered with oxygen is loLtimes greater than from caesiated filaments of orygen-free tungsten. Hence, an experimental method by means of electron emission measurements may he devised to determine the fraction of a tungsten surface covered with oxygen a t a given tem~eratureand oxygen partial pressure. ~From the catalytic point of view results of interest are obtained with hydrogen and oxygen in contact with tungsten. Up to 1500DK.the reaction occurring is practically exclusively the formation of WOa, with no dissociation of hydrogen into atoms or reaction with oxygen t o form water. Here is a case of a reaction (2H2 01) being slowed down a t a surface. The same is true of caesium and oxygen which do not react on a tungsten surface a t temperatures a t which, in the gas phase, ready reaction would occur. ~
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The following is a brief abstract of PROPESSOR BODENSTEIN'S paper: The catalytic oxidation of ammonia cannot be a simple reaction according to the equation 6Hn0, 4NH8 50%= 4 N 0 especially because there is always formation of nifrogen, though subordinate to that of nitric oxide. The mechanism assumed is: OX = HNO HnO, fol%wed either hy 1. NHa 2. HNO O* = HN08, or by NHs = N2 H 2 0 Ha 3. HNO where, of course, HNOI is decomposed into NO and HBO,while O2 and Ha are burnt t o H 2 0 in later steps. Calculation of the relative yield of NO and N2 for gases with different ratios of O2:NH3were made on the assumption that every collision of an HNO just formed with O2 or with NHI gives rise to reaction 2 or 3. Older experiments made by Andrussow gave results which agree with those calculated only for the equivalent mixture hut differ for other mixtures in a direction accounted for by the fact that on the surface of the catalyst the excess of the excess-gas must be raised by the sudden reaction. New experiments with a ferric oxide-bismuth oxide catalyst in which the reaction occurs slowly gave results which agree with the calculation as well as the other features of the reaction do.
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According to DR. PERRIN, When a light quantum is absorbed by a fluorescent substance, an excited molecule is formed which has the power of reverting spontaneously t o its normal state, with the emission of light. This process is not instantaneous, but the excited molecule possesses a certain "mean life" which M. Perrin has been able t o evaluate by studying the polarization of the fluorescence light. The results indic3te t h a t an excited molecule of a fluorescent dyestuff is not affected by collisions with molecules of the solvent but that the
presence in its vicinity of another molecule of the same substance, in the normal state, may cause i t t o hecome deactivated without light emission. Consequently the mean life is shorter the more concentrated the solution, which is in line with the well-known fact that the fluorescence efficiency increases with dilution. This "deactivation by molecular induction" is interpreted as a resonance phenomenon, where the energy of excitation is transformed into kinetic energy of the resonating molecules. I n accordance with this view, it may also he produced by adding t o the solution another dyestuff, having an absomtion band sufficiently dose to that of the fluorescent substance. Deactivation without light emission is, however, also produced by certain classes of colorless substances, like iodides, phenols, and aromatic amines. These same substances are known to act as inhibitors in autovidation reactions, now generally considered to be chain reactions, and M. Perrin suggests that their inhibitory action iscdue t o their power of deactivating the. active molecules which form the links in the reaction chain.
MR. C. N. HINSHELWOOD, Fellow of Trinity College, Oxford, and author of "Kinetics of Chemical Change in Gaseous Systems" spoke on the subject, "Catalysis and Chain Reactions." Mr. Hinshelwood called attention to the essential similarity of catalytic and noneatalvtic reactions, and then proceeded to d/rcuss in some detail the nature of the soc:rllcd thermal chain rcaetiona. These arc rrnctiods in which newly-formed molecules of product are supposed to hare the prwcrty of activating frwh molrclrlea of reacrant, so that the impulse to react is passed along a n imaginary chain of reactant molecules. The PROFESSOR M. POLANYIO*. THE K~~~~~ I T J I~~~~~~~~ ~ ~ ~ FOR ~ speculations ~ ~ of Semenoff were briefly disP ~ u s ~ cAND n ~ ELECTRO-CHEMISTRY,cussed, and were applied in particular to BERLIN those curious cases of thermal explosion which Professor Polanyi gave a course of take place only between sharply-defined limits pre,,. T~~ was reac lectures on chemical activation in the symposium on chemical kinetics that the phenomena were due to a balance recently held at the university of hetween two opposing tendencies-the one Minnesota, being the "breaking" of chains a t the walls of the containing vessel, the other being the "breaking" of chains by collision with other molecules. The first is the more efficient a t low pressures, the second is more efficienta t high pressures. I n the case of mixtures of hydrogen, sulfur vapor, phosphorus vaDor, n e oxygen, there is this intermediate region in which neither process . . o .r ~ h o.s ~ b iwith ~. is sufficiently effective t o prevent propagation of the chains. The efficacy of small quantities of nitrogen peroxide in promoting oxidation reactions was also dealt with. This is a case of the so-called "trace catalysis."
PROFESSOR M. POLANYI has summarized in a very interesting and stimulating lecture his studies on the characteristics of some of those chemical
reactions which he terms "elementary reactions" and whic!~a r e t o o f a s t investigated by ordinary means.
t o be
Using very ingenious methods he has studied in great detail the rates of reaction of dilute alkali metal vapors with gaseous halogens,. or with vaporized halogen salts, and the accompanying chemiluminescence. The conclusion reached in these studies is that such reactions proceed generally in two steps. First, atoms of alkali metals react with halogen molecules farming alkali halide and a free atom of halogen, as for instance in the process: Na CI2 = NaCl CI. These reactions, in so far as they are exothermic, proceed on every collision of the gaseous reactants and do not require the "activation energy" typical of slaw chemical reactions. The halogen atoms set free could react further with alkali atoms, thus: C1 Na = NaC1. However, as has been shown by earlier theoretical considerations of Polanyi, Herzfeld, and Christiansen, suchdirect addition processes are incompatible with the principles of the theory of chemical reactions in gases. And indeed, Dr. Polanyi finds now that halogen atoms do not react in this way. Instead, a reaction takes place between halogen atoms and diatomic alkali molecules which latter are present in a smaller concentration in alkali vapors. Thus, for instance: C1 N a = NaCl Na. From the dependence of this reaction on temperature Dr. Palanyi is able to calculate the heat of dissociation of sodium molecules into atoms and finds a perfect agreement with data otherwise obtained. The energy set free in the reaction of halogen atoms with alkali molecules is transferred to that a l M i atom which remains free and serves t o excite it to a higher quantum level. The return to the normal state of the atom is accompanied by emission of excess energy as radiation, the resonance D lines in case of sodium atoms. Thus is explained why these reactions, while proceeding at relatively low temperatures, are accompanied by a bright chemiluminescent light of discrete wave lengths.
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The lecture was made even more interesting by a very successful demonby Dr. Polanyi of the chemiluminescence accompanying the re-
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action between s o d i u m and mercuric chloride vapors. DR. BONHOEFFER discussed the transformation of orthohydrogen into parahydrogen. This is accomplished by passing hydrogen through porous charcoal a t low temperatore, the charcoal irrving as catalyst. A t room tempcraturc thuc are 75 parts of orthohydragcn to 25 partr of parahydrogen; a t the temperature of liquid air the parahydrogen rises t o 50 per cent; while a t the temperature of liquid hydrogen i t reaches the high value of 99.7 per cent, leaving only 0.3 per cent of orthohydrogen. ~
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The physical properties of the two types of hydrogen are somewhat different, particularly their specific heats. It is assumed that the nuclei in the two atoms of a molecule of orthohydrogen are spinning in the same direction, while those of parahydrogen are spinning in opposite directions.
