Allan T. Gwathmey and His Contributions to the Science of Catalysis

Jun 3, 1983 - It was my privilege to be a student and long-time friend of Allan Talbott Gwathmey who by his personality and experimental observations ...
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Allan T. Gwathmey and His Contributions to the Science of Catalysis HENRY LEIDHEISER, JR. Lehigh University, Department of Chemistry and Center for Surface and Coatings Research, Bethlehem, PA 18015

It was my privilege to be a student and long-time friend of Allan Talbott Gwathmey who by his personality and experimental observations played an important role in directing the attention of scientists to the role of the atomic geometry of catalysts in controlling the rates of heterogeneous catalytic reactions. I accept with pleasure the invitation to attempt to place his work in perspective. It is my intention to give a picture of the man as well as the technical contributions he made in the field of catalysis. I will draw on two previous publications (1,2) where appropriate. The Man A l l a n Gwathmey was born i n Richmond, V i r g i n i a on J u l y 29, 1903. He attended preparatory school i n Richmond and r e c e i v e d h i s B.S degree from V i r g i n i a M i l i t a r y I n s t i t u t e i n 1923. Following s e v e r a l years of employment as an engineer, he e l e c t e d to r e t u r n to school and he earned the B.S. degree i n E l e c t r o c h e m i c a l Engineering from Massachusetts I n s t i t u t e of Technology. After s e v e r a l years of i n d u s t r i a l research, A l l a n Gwathmey entered the Graduate School of the U n i v e r s i t y of V i r g i n i a during the severe depression years of the 1930 s and earned the Ph.D. degree i n Chemistry i n 1938. He continued at the U n i v e r s i t y of V i r g i n i a as a research a s s o c i a t e u n t i l h i s appointment as a member of the Chemistry Department f a c u l t y i n about 1947, and he remained a member of the f a c u l t y u n t i l h i s death i n 1963. His i n t e r e s t s at the U n i v e r s i t y of V i r g i n i a were campus wide. He l i v e d f o r many years i n the Colonnade Club on the Lawn, that b e a u t i f u l terraced green l i n e d w i t h grand t r e e s , that connects C a b e l l H a l l with the b u i l d i n g that symbolizes the Univers i t y , the Rotunda. He fought i n many ways to r e t a i n the d i g n i t y and charm of the Colonnade Club to the end that i t was the f o c a l point f o r f a c u l t y s o c i a l l i f e . He served on the U n i v e r s i t y T

0097-615 6/8 3/0222-0121$06.00/0 © 1983 American Chemical Society

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F i g u r e 1. A l l a n T a l b o t Gwathmey. P h o t o g r a p h t a k e n i n 1955. ( R e p r o d u c e d w i t h p e r m i s s i o n from R e f . 2.)

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Senate and d i d what he could to encourage deemphasis of i n t e r c o l legiate athletics. I t i s i n t e r e s t i n g to conjecture what h i s view would be i f he l i v e d during the 1981 and 1982 seasons when Ralph Sampson was the outstanding s t a r of i n t e r c o l l e g i a t e b a s k e t b a l l . His viewpoints with respect to a t h l e t i c s were d i f f e r e n t from those of many of h i s f r i e n d s , a s s o c i a t e s , and students, but these views d i d not i n h i b i t h i s f r i e n d s h i p s . He was c a l l e d on by the President of the U n i v e r s i t y many times to host d i s t i n g u i s h e d v i s i t o r s because of h i s knowledge of the U n i v e r s i t y , h i s charm and h i s genteel manner. He was a constant thorn i n the s i d e s of deans and p r e s i d e n t s when they were not a g g r e s s i v e l y seeking to b u i l d e x c e l l e n c e i n t o departments. He played important r o l e s i n encouraging wealthy alumni to support t h e i r u n i v e r s i t y . His i n t e l l e c t u a l i n t e r e s t s were broad. He taught a course i n a e s t h e t i c s i n the Department of Philosophy, and he was w r i t i n g a book, which he never completed, on economics. Professor Gwathmey treated h i s graduate students as one b i g f a m i l y . They were welcome to confide i n him and to seek h i s adv i c e on t e c h n i c a l as w e l l as n o n - t e c h n i c a l matters. His o f f i c e door was always open and he would i n t e r r u p t whatever he was doing to t a l k to students. Since he married l a t e i n l i f e and had no c h i l d r e n of h i s own, h i s students f i l l e d a v o i d i n h i s l i f e . When things d i d not go w e l l i n the l a b o r a t o r y or when the demands of the experiment were greater than the a v a i l a b l e resources, h i s f a v o r i t e expression was "The toughening d i s c i p l i n e of a complex experiment." Years l a t e r when h i s students communicated among themselves by l e t t e r s , wire or telephone, i t was not unusual to have a p o s t s c r i p t which read TTDOACE. He loved h i s n a t i v e s t a t e with a passion. The beauty of the Lawn at the U n i v e r s i t y , the S p i r i t of VMI, and h i s admiration f o r Thomas J e f f e r s o n were o f t e n subjects f o r comment or d i s c u s s i o n among h i s f r i e n d s and almost always crept i n t o h i s p u b l i c l e c t u r e s . The l o s s of W i l l i a m Barton Rogers to Massachusetts, and h i s founding of MIT i n the north r a t h e r than at W i l l i a m and Mary, bothered him enormously. He p r e v a i l e d upon the V i r g i n i a Academy of Science to fund an i n s t i t u t e devoted to b a s i c research. They did i n 1948 and the Commonwealth of V i r g i n i a i n 1949 provided a grant of $20,000 plus f r e e r e n t a l of an o l d b u i l d i n g i n a park i n Richmond and the V i r g i n i a I n s t i t u t e f o r S c i e n t i f i c Research came i n t o being. V i r g i l Straughan and I were the f i r s t f u l l - t i m e employees, and the hardships endured i n p u l l i n g an i n s t i t u t i o n up by i t s bootstraps were only bearable because of the enthusiasm and i n s p i r a t i o n of A l l a n Gwathmey. This i n s t i t u t i o n grew to a s t a f f of approximately 40 and s u f f i c i e n t funds were r a i s e d to b u i l d a modern l a b o r a t o r y on 20 acres of ground i n the b e a u t i f u l west end of Richmond. The b u i l d i n g was dedicated i n J u l y 1963 and was named the A l l a n T a l b o t t Gwathmey Laboratory. He l i v e d to see i t completed and occupied. The I n s t i t u t e i s now part of the U n i v e r s i t y of Richmond.

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The w r i t t e n word and the spoken word were important to Dr. Gwathmey. He would d r a f t a l e t t e r , put i t aside f o r s e v e r a l days, rewrite the l e t t e r , perhaps r e v i s e i t s e v e r a l more times before i t was considered worthy of m a i l i n g . Manuscripts were r e v i s e d many times before submittal f o r p u b l i c a t i o n and he i n s i s t e d upon r e p l i c a t i o n of research r e s u l t s before he would accept them as c o r r e c t . S o c i a l events were planned c a r e f u l l y and meetings w i t h important people, e s p e c i a l l y on a c o n t r o v e r s i a l i s s u e , involved strategy p l o t t i n g of a high order. He discussed strategy o f t e n with c l o s e a s s o c i a t e s and enjoyed the planning and the c o n f r o n t a t i o n w i t h a r e l i s h that was contagious. A l l a n Gwathmey was not blessed with good h e a l t h and was a rather f r a i l c h i l d . His f a t h e r died while A l l a n was young, and t h i s event made him aware of the importance of good h e a l t h . In the e a r l y 1950*3 i t was recognized that he had a severe case of diabetes and he soon became a " b r i t t l e d i a b e t i c " . His pockets always contained sugar, candy or f r u i t so that he could t i t r a t e the i n j e c t e d i n s u l i n as h i s body advised him. Blackouts were not uncommon i n the e a r l y days of h i s treatment and one of them r e s u l t e d i n a broken knee. In 1961 he began to experience impairment i n the muscles that c o n t r o l breathing, swallowing and t a l k ing. Chemotherapy was of some help, but a creeping p a r a l y s i s began that culminated i n h i s death on May 12, 1963. The l a s t few months of h i s l i f e were d i f f i c u l t beyond expression, but he never l o s t h i s optimism and h i s i n t e r e s t i n the world around him.

The

S c i e n t i s t and His

Contributions

A l l a n Gwathmey began h i s studies of surface s t r u c t u r e as r e l a t e d to the a c t i v i t y of d i f f e r e n t c r y s t a l faces of a s i n g l e c r y s t a l i n 1934, at which time he decided to u t i l i z e low v o l t a g e e l e c t r o n d i f f r a c t i o n as a technique i n studies l e a d i n g to the Ph.D. degree. He was captivated by the d i f f r a c t i o n experiments reported by Davisson and Germer i n 1927 and he recognized the a p p l i c a b i l i t y of t h i s phenomenon to a b e t t e r understanding of the surface p r o p e r t i e s of metals. In the s t y l e of the times, he b u i l t the apparatus himself, n e u t r a l i z e d the s t r a y f i e l d s that might i n t e r f e r e with the t r a j e c t o r y of the d i f f r a c t e d e l e c t r o n beams, and developed the technique f o r preparing, c u t t i n g and s u r f a c i n g the copper s i n g l e c r y s t a l s to be used as samples. He received no t e c h n i c a l support from h i s t h e s i s advisor, A. F. Benton, and moral support only i n the form of a pat on the back and a "get to i t " . During the course of the d i f f r a c t i o n experiments he decided to study the p r o p e r t i e s of an o x i d i z e d copper surface. His experimental sample was shaped i n the form of a sphere with a small h o l d i n g shaft so that he could manipulate the sample i n the d i f f r a c t i o n chamber and expose d i f f e r e n t c r y s t a l faces to the e l e c t r o n beam. The o x i d a t i o n of the e l e c t r o p o l i s h e d sphere r e s u l t e d i n the development of a b e a u t i f u l i n t e r f e r e n c e c o l o r pattern

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which r e f l e c t e d the symmetry of the c r y s t a l . This observation was the beginning of h i s d e d i c a t i o n to the a p p l i c a t i o n of metall i c s i n g l e c r y s t a l s to s t u d i e s of s u r f a c e phenomena. A l l a n Gwathmey began h i s work i n c a t a l y s i s when the emphasis of much of the work i n the f i e l d was an attempt to understand the k i n e t i c s of the r e a c t i o n s by means of adsorption s t u d i e s . The development of the Brunauer-Emmett-Teller r e l a t i o n s h i p allowed one to c a l c u l a t e the surface areas of c a t a l y s t s and to determine the amounts of adsorption and the energetics of the adsorption process. I t was a time when t y p i c a l papers with a c a t a l y t i c o r i e n t a t i o n were f i l l e d with information on adsorption h y s t e r e sis, heats of adsorption, changes i n surface area with heat treatment, and pore s i z e s . People such as Hugh Taylor of P r i n c e ton played a dominant r o l e i n molding opinion and i n s e t t i n g the standards f o r research i n c a t a l y s i s and i t was Hugh Taylor that Dr. Gwathmey took as h i s f a v o r i t e antagonist i n meetings such as the Gordon Conference on C a t a l y s i s . His o b j e c t i o n to the t h r u s t of the research was that i t often focused on elaborate measurements on poorly prepared m a t e r i a l s . He fought f o r experiments which were c a r r i e d out on w e l l c h a r a c t e r i z e d m a t e r i a l s . Others who a l s o began preaching the same sermon included F. P. Bowden w i t h h i s b e a u t i f u l work on the surface energy of mica c r y s t a l s and E. W. M i i l l e r with h i s pioneering work on f i e l d emission and l a t e r f i e l d ion emission experiments. The f i r s t p u b l i c a t i o n of h i s work was i n the Transactions of the E l e c t r o c h e m i c a l Society (_3) i n which he described the a n i s o t r o p i c p r o p e r t i e s of a copper s i n g l e c r y s t a l submitted to various chemical and e l e c t r o c h e m i c a l e t c h i n g treatments. His second paper described the method f o r preparing, shaping, and s u r f a c i n g copper s i n g l e c r y s t a l s p r i o r to an experiment (4) and r a p i d l y f o l l o w i n g papers described the b e a u t i f u l i n t e r f e r e n c e patterns obtained when an e l e c t r o p o l i s h e d copper sphere was o x i d i z e d i n a i r 05,6). The f i r s t p u b l i c r e p o r t , other than l o c a l presentat i o n s through the V i r g i n i a Academy of Science, on c a t a l y s i s appeared i n 1942 i n which he described the surface rearrangements that occurred on copper s i n g l e c r y s t a l s as a consequence of the hydrogen-oxygen r e a c t i o n . In h i s own words (7): "The r e a c t i o n between hydrogen and oxygen renders the surface s u f f i c i e n t l y mob i l e to develop c e r t a i n c r y s t a l f a c e t s . In order to produce the rearrangement, the e f f e c t i v e temperature at the surface of the metal when the r e a c t i o n i s taking place must be considerably above the measured temperature of the r e a c t i o n v e s s e l . Since the r e a c t i o n between hydrogen and oxygen becomes appreciable at the same temperature at which the development of f a c e t takes p l a c e , t h i s experiment suggests that these f a c e t s may be r e l a t e d to the p o s i t i o n s of enhanced c a t a l y t i c r e a c t i v i t y f o r t h i s part i c u l a r r e a c t i o n . " The work on the hydrogen-oxygen r e a c t i o n on copper and n i c k e l was f u r t h e r elaborated on by L e i d h e i s e r (8), by Cunningham (9) , and by Wagner (,10).

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Although the work on the hydrogen-oxygen r e a c t i o n received a t t e n t i o n , the l a r g e d i f f e r e n c e in. the a c t i v i t y of the d i f f e r e n t c r y s t a l faces of n i c k e l f o r the carbon monoxide decomposition r e a c t i o n , 2C0 = C + CO2, was d r a m a t i c a l l y shown by the d i f f e r e n t r a t e s of carbon d e p o s i t i o n (11). See Figure 2 . The a b i l i t y to d i s p l a y t h i s d i f f e r e n c e i n c a t a l y t i c a c t i v i t y by means of a photograph aided i n convincing the unbeliever of the importance of surface geometry of atoms i n c a t a l y t i c r e a c t i o n s . The superb photographs beginning to emerge from f i e l d emission and i o n emiss i o n microscopy provided complementary support f o r the concept. Another c a t a l y t i c r e a c t i o n — t h e d e p o s i t i o n of a metal on the surface of a d i f f e r e n t metal using a reducing agent—was a l s o shown to be a n i s o t r o p i c i n nature. The d e p o s i t i o n of cobalt from a potassium formate melt, the d e p o s i t i o n of n i c k e l from a potassium formate melt, and the d e p o s i t i o n of n i c k e l from a hypophosp h i t e s o l u t i o n a l l occurred on copper s i n g l e c r y s t a l s at rates which depended on the c r y s t a l face exposed at the surface (12). This work was c a r r i e d out i n Dr. Gwathmey's l a b o r a t o r y but he d i d not wish to be a coauthor s i n c e he had not contributed to the planning or execution of the experiments. Perhaps the most important c o n t r i b u t i o n that Dr. Gwathmey made was to develop the r e c o g n i t i o n among those working i n m a t e r i a l s science that the surface p r o p e r t i e s of m a t e r i a l s were a n i s o t r o p i c and that d i f f e r e n t c r y s t a l faces of the same m a t e r i a l had d i f f e r e n t p r o p e r t i e s . He demonstrated t h i s phenomenon i n c a t a l y s i s , corrosion, electrochemical properties, electrodeposition, wetting, f r i c t i o n , wear, o x i d a t i o n , and r e a c t i o n with hot gases such as bromine, c h l o r i n e , and hydrogen s u l f i d e . He developed the r e c o g n i t i o n that anisotropy of surface behavior was u n i v e r s a l . A chance meeting with A. B. Winterbottom of the U n i v e r s i t y of Trondheim l e d Gwathmey to apply the technique of e l l i p s o m e t r y to non-destructive studies of the r a t e of growth of oxide f i l m s on s p e c i f i c c r y s t a l faces of copper. The h e r o i c e x p l o i t of Tronstad, the developer of the technique as a p p l i e d to metal surface s t u d i e s , and h i s death during a r a i d on a heavy water plant i n Norway during WW I I , gave the technique an e x o t i c f l a v o r that appealed to Dr. Gwathmey s imagination. He gave the a s s i g n ment to h i s student, Fred W. Young, J r . , who along with f e l l o w student John Cathcart brought the technique to the point that i t was able to provide p r e c i s e , q u a n t i t a t i v e information on the thickness of an oxide f i l m on a s i n g l e c r y s t a l copper substrate. This technique was f u r t h e r developed by graduate student Jerome Kruger, who l a t e r a p p l i e d the technique to many i n t e r e s t i n g c o r r o s i o n problems at the N a t i o n a l Bureau of Standards. Another student of Prof. Gwathmey s, Kenneth Lawless, spent a year i n Trondheim working with Prof. Winterbottom. Coincident with the research on the anisotropy of the chemic a l behavior of metal s i n g l e c r y s t a l s there was growth i n the development of the concept of imperfections, both s t r u c t u r a l and chemical, i n semiconductors and metals. Two leaders i n the f i e l d , John M i t c h e l l and N i c o l a s Cabrerra, j o i n e d the physics f a c u l t y at the U n i v e r s i t y of V i r g i n i a . A strong bond of f r i e n d 1

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F i g u r e 2. The s e l e c t i v e d e p o s i t i o n o f c a r b o n on t h e (111) f a c e s o f a n i c k e l s i n g l e c r y s t a l d u r i n g t h e c a t a l y t i c decompos i t i o n of c a r b o n monoxide a t 550 C. ( R e p r o d u c e d from R e f . l l . C o p y r i g h t 1948, A m e r i c a n C h e m i c a l S o c i e t y . )

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ship b u i l t up among these men, e s p e c i a l l y between M i t c h e l l and Gwathmey. This f r i e n d s h i p and a j o i n t empathy f o r the a e s t h e t i c continued u n t i l Dr. Gwathmey s death. Dr. M i t c h e l l was a tower of strength f o r Roberta Gwathmey during the d i f f i c u l t two years preceding h i s decease. The f i r s t s i g n i f i c a n t d i s c u s s i o n of the e f f e c t of d i s l o c a t i o n s , l a t t i c e d e f e c t s , and e l e c t r o n i c and geometric f a c t o r s on the c a t a l y t i c p r o p e r t i e s of s i n g l e c r y s t a l s occurred i n a paper with Cunningham (13). This same paper i n cluded studies of the hydrogénation of ethylene, the f i r s t c a t a l y t i c r e a c t i o n that was studied by Gwathmey that d i d not lead to surface rearrangement. The concept that c r y s t a l o r i e n t a t i o n and defects j o i n t l y were important i n c o n t r o l l i n g surface r e a c t i v i t y was c a r r i e d f o r t h by Cathcart at the Oak Ridge N a t i o n a l Laboratory (ORNL). Cathcart and colleagues at ORNL observed that high rates of o x i d a t i o n of copper occurred on those c r y s t a l faces i n which there were s e v e r a l p o s s i b l e e p i t a x i a l r e l a t i o n s h i p s between the copper substrate and the cuprous oxide o x i d a t i o n product and that the low r a t e s of o x i d a t i o n occurred on those faces where there was one dominant o r i e n t a t i o n a l r e l a t i o n s h i p . Benard and colleagues i n P a r i s had e a r l i e r shown that the o x i d a t i o n of copper occurs i n i t i a l l y at l o c a l s i t e s that increase i n s i z e by l a t e r a l growth. Imperfections tended to be a maximum on those faces with m u l t i p l e o r i e n t a t i o n a l r e l a t i o n s h i p s because of l a t t i c e mismatch i n those regions where merging occurred. P r e c i s e s t u d i e s of the s t r u c t u r a l imperfections i n copper s i n g l e c r y s t a l s were c a r r i e d out by F. W. Young, J r . a f t e r he received the Ph.D. degree and j o i n e d the S o l i d State Branch of ORNL. Young developed etchants that brought out the d i s l o c a t i o n s which i n t e r s e c t e d the surface. He was thus able to determine the number of imperfections that was present as a consequence of the s i n g l e c r y s t a l growth process and to determine those that were introduced by v a r i o u s mechanical treatments. Many of the metals with which h i s graduate students worked were very d i f f i c u l t to shape when i n the form of a pure s i n g l e c r y s t a l . Metals such as zinc r e a d i l y s p l i t along (0001) planes; indium was almost as s o f t as c o l d b u t t e r ; lead and copper deformed under t h e i r own weight i f not supported p r o p e r l y ; and gold tended to smear rather than cut when handled with a normal c u t t i n g t o o l on a l a t h e . I t was necessary to develop proper c u t t i n g speeds, rake angles, and c u t t i n g angles f o r each d i f f e r ent metal. Dr. Gwathmey decided to develop h i s own machine shop and he was fortunate to f i n d a t a l e n t e d machinist i n the person of V i r g i l Straughn. This machine shop grew i n competence i n handling s i n g l e c r y s t a l s of metals such that s i n g l e c r y s t a l s of lead and zinc could be machined i n the form of spheres where r e c r y s t a l l i z a t i o n was confined to the outer l a y e r i n the case of lead and where shearing was prevented i n the case of z i n c . Dr. Gwathmey s a c t i v i t i e s a f t e r about 1944 f i l l e d the e n t i r e lowest f l o o r of Cobb Chemical Laboratory. This f l o o r was known as the sub-basement, even though i t was above ground l e v e l on one 1

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s i d e . The drainage system f o r the organic chemistry l a b o r a t o r i e s on the f l o o r above passed through t e r r a c o t t a pipes below the c e i l i n g l e v e l i n the sub-basement. The passage of time r e s u l t e d i n sagging of the pipe i n some l o c a t i o n s and the a c i d s and organi c solvents that improperly entered the drainage system caused d e t e r i o r a t i o n of the cemented j o i n t s . Students constructed a secondary drainage system with the a i d of funnels and tubing to c o l l e c t the exudate and c a r r y i t to the s i n k . The n o v e l t y of the arrangement was always a source of d i s c u s s i o n with many of the famous s c i e n t i s t s who v i s i t e d the l a b o r a t o r y . When d i s agreements broke out between the " o r g a n i c s " and the " p h y s i c a l s " , the " o r g a n i c s " on the f l o o r above held the upper hand s i n c e they had recourse to lachrimators with which Prof. Lutz's students o c c a s i o n a l l y worked. Although Dr. Gwathmey had a good sense of humor there i s only one case where I can remember that laughter overwhelmed him. An undergraduate student had begged f o r summer employment and Dr. Gwathmey took him i n t o the group and suggested that the graduate students might u t i l i z e h i s s e r v i c e s i n some of the more r o u t i n e operations that were performed. The young man proved to have l i t t l e c a p a b i l i t y f o r experimental work and e s p e c i a l l y so f o r s i n g l e c r y s t a l s that had to be handled with gentleness and l o v i n g care. As a consequence, the assignments that were given to the undergraduate ended up being mundane and u n i n t e r e s t i n g . One day he v i s i t e d Prof. Gwathmey to share h i s unhappiness. He rested against the open o f f i c e door during the conversation and when i t was completed, he turned to leave the room. Unfortun a t e l y , h i s l e f t r e a r pocket had become ensnared by the doorknob, h i s foot prevented the door from f o l l o w i n g h i s departure, and the rear of h i s pants was t o r n s e v e r e l y . Dr. Gwathmey was very kind and compassionate about h i s misfortune, but a f t e r the student had l e f t the b u i l d i n g to change c l o t h i n g , he was convulsed with laughter that could not be c o n t r o l l e d f o r s e v e r a l minutes. The i n c i d e n t r e i n f o r c e d very c o n v i n c i n g l y the " a l l thumbs" l a b e l with which the graduate students had i d e n t i f i e d the undergraduate. Many s c i e n t i s t s came by to v i s i t P r o f . Gwathmey and each v i s i t o r represented a challenge to convince the v i s i t o r of the s i g n i f i c a n c e of metal s i n g l e c r y s t a l s as research t o o l s and as a c u t t i n g edge of m a t e r i a l s s c i e n c e . A l o c a l carpenter was given the assignment to construct a d i s p l a y case i n which the s i n g l e c r y s t a l s could be e a s i l y viewed. Prof. Gwathmey maintained the case, f i l l e d with metal s i n g l e c r y s t a l s e x h i b i t i n g some important principle, i n his office. I t was a d e l i g h t to see such w e l l known s c i e n t i s t s as J . Beams, W. A. Noyes, J r . , H. H. Storch, N. F. Mott, H. E y r i n g , and C. J . Davisson l e a n i n g over the case and being e n t h r a l l e d by the enthusiasm of t h e i r host. Prof. Gwathmey's eyes would become teared when he became emotionally involved i n h i s subject and t h i s act had a f a v o r a b l e e f f e c t on the v i s i t o r who recognized the s i n c e r i t y of the speaker.

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Literature Cited 1. Leidheiser, H. Jr. Virginia J . Science 1964, 15 (1), 1. 2. Leidheiser, H. Jr. Corrosion 1976, 32, 191. 3. Gwathmey, A. T.; Benton, A. F. Trans. Electrochem. Soc. 1940, 77, 211. 4. Gwathmey, A. T . ; Benton, A. F. J . Phys. Chem. 1940, 44, 35. 5. Gwathmey, A. T.; Benton, A. F. J . Chem. Phys. 1940, 8, 431. 6. Gwathmey, A. T.; Benton, A. F. J . Phys. Chem. 1942, 46, 969. 7. Gwathmey, A. T.; Benton, A. F. J . Chem. Phys. 1940, 8, 569. 8. Leidheiser, H. J r . ; Gwathmey, A. T. J . Am. Chem. Soc. 1948, 70, 1200. 9. Gwathmey, A. T.; Cunningham, R. E. J . Chem. Phys. 1954, 51, 497; Cunningham, R. E . ; Gwathmey, A. T. J. Am. Chem. Soc. 1954, 76, 391. 10. Wagner, J . B. J r . ; Gwathmey, A. T. J . Am. Chem. Soc., 1954, 76, 390. 11. Leidheiser, H. J r . ; Gwathmey, A. T. J . Am. Chem. Soc. 1948, 70, 1206. 12. Leidheiser, H. J r . ; Meelheim, R. J . Am. Chem. Soc. 1949, 71, 1122. 13. Cunningham, R. E.; Gwathmey, A. T. Adv. in Catalysis 1957, 9, 25. Received November 17, 1982