ffOUI~N&L OF COLLOID SCIt lNCE 11,296-298 (1956)

Sir Eric Rideal--An Appreciation

Heredity, Sanderson's preparatory school at Oundle, and Cambridge in the late-classical period of J. J. Thomson served to mold and determine the future scientific career of Sir Eric Rideal. The processes of learning were complete by the time World War I broke out in the summer of 1914. The first academic year after the war Rideal spent in the University of Illinois. I t was perhaps fortunate for England that a large state university contrasted so radically with Cambridge. Smoking, also, was, at that time, prohibited on the Illinois campus. Rideal found himself much more at home on the Princeton campus, which he visited several times during the year. He did not find in Princeton what proved later to be Princeton's principal asset to him. I t was on the boat in 1920 returning to England that he first met the gracious Princeton lady who was subsequently to become his charming wife.

The threat of submarine warfare compelled England to take steps in 1916-17 to learn how the nitrogen of the air could be fixed and the ammo- nia converted to nitric acid. Rideal and Partington were withdrawn from the Somme barges where, as lieutenants in the Royal Engineers, they had supervised water supplies for the troops. Together they elucidated the catalytic ammonia oxidation process on platinum gauze and formulated pilot plant and production procedures. Greenwood had a small group of men working on synthesis proper, he being the only man with previous experience in high-pressure synthesis. The writer was assigned the task of learning how to produce the nitrogen-hydrogen mixture. Since this was a major fraction of the total cost from an economic standpoint, it was de- cided that Rideal should join in the effort. There ensued a happy, fruitful eighteen months of collaboration. A number of problems for the Army as well as in the production of synthesis gas were solved. We were dubbed the Siamese twins, and it would be difficult to decide who was responsible for this or that advance. And, together, during the same period, we wrote a book Catalysis in Theory and Practice to try to define a scientific content of the subject. A good friend who reviewed the book guessed which of us had written the individual chapters. His guess was wrong because he used the wrong measuring stick.

We parted company early in 1919, each resolved to find some more sci- ence to put into a second edition of the book if it should ever reach such a state. Rideal elected to pursue kinetics, the writer to concentrate on ad- sorption by catalysts. That was the way we started, but over the years we each crossed over from one domain to the other.

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From these early years a few researches may be cited. With Hurst, Rideal examined the ratio CO :H2 burnt in presence of copper catalysts promoted with palladium. With Norrish he studied the catalytic influence of oxygen in reaction at a liquid sulfur-hydrogen interface. Together, also, they studied the influence of surfaces on the reaction between ethylene and bromine vapor which indicated a nonhomogeneous process, catalyzed by glass, cetyl alcohol, or paraffin wax to varying degrees. With a joint study on the sensitization by chlorine of hydrogen-oxygen mixtures to visible light, Norrish was launched, as were so many of Rideal's subsequent stu- dents, on the pathway to academic honors and chairs of chemistry.

A new phase in Rideal's career was developing simultaneously which culminated in the newly established school and chair of Colloid Science at Cambridge. In 1924 he was examining the destruction of rennin at an air- liquid interface and with Sehofield was examining mono-layers on water as two-dimensional gases. They showed that as the length of the hydro- carbon chains in the fatty acids increases, the lateral adhesion between the gaseous films in the surface increases. The measurements of surface pressure using the Langmuir trough led also to measurements of "surface potential," the contact potential between the liquid and air. Early measurements by Guyot and Frumkin gave place to the detailed studies of Sehulman and Rideal (1931). They compared surface potentials with surface pressures and refined the techniques of the potential measurement.

Side by side with the work on surface films the work on solid surfaces was prosecuted vigorously. Undoubtedly the most important work in the Cambridge School in this period was the work initiated and carried through by Roberts on the adsorptive properties of clean tungsten filaments. This work ushered in an entirely new era in the investigation of metal surfaces. The incredibly accurate measurements of Roberts on flashed tungsten fila- ments indicating the rapidity of many processes of chemisorption on clean surface, the use of Pirani gauges for measuring adsorption at low pressures of the order of 10 -5 ram., the use of the accommodation coefficient of helium and neon to follow the adsorption process, all these techniques opened up a new era in adsorption by metals which Beeck, Tompkins, and many others have developed from their original beginnings in Cambridge. In the early thirties the advent of deuterium opened up a new phase of kinetic studies both homogeneous and heterogeneous. Farkas and Melville as postdoctoral students in Rideal's laboratory made basic advances in this area. The existence of isotopic exchange side by side with hydrogenation of ethylene was a major result from these studies.

Toward the end of the 1930's the study of reactions in surface films was in full swing including physical processes of adsorption and penetration as well as chemical reactions proper. Differences of penetration by sodium cetyl sulfate with films of cholesterol and cholesterol acetate had signifi- cance in the interpretation of biological processes as, for example, blood

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lyses. Interaction between amine films and a soluble acid substance, e.g., phenol, gave no change in surface pressure but change in the dipole mo- ment vector. Dihydroxy phenols could give rise to cross-linking. Hydroly- sis of esters was followed by change in surface potential as well as surface area. The oxidation of the double bond in oleic acid films with dissolved permanganate was shown to be a function of surface pressure; at low pres- sures the double bond was in the surface layer and oxidizable, at high pressures it was squeezed out of the surface and lined up in the hydrocarbon chain, inaccessible to the oxidant.

During World War II Rideal was engaged once more in scientific service to his country, this time at a high level of responsibility. Physical chemists have reason for gratitude to him also for his Presidency of the Faraday Society continuously during all the long war years. This unique record is paralleled by his Presidency both of the Chemical Society and of the So- ciety of Chemical Industry, surely a trio of honors not achieved by any other. The Professorship in Colloid Science lasted from 1930 to 1946, when Rideal succeeded Sir William Bragg and followed in the footsteps of Davy and Faraday as Fullerian Professor of Chemistry in the Royal Institution and Director of the Davy-Faraday Laboratory. This phase lasted three years, from 1946 to 1949. One suspects that the erstwhile Cambridge don missed the youth and vitality of the undergraduate. He returned to uni- versity work as Professor of Physical Chemistry at King's College, London, from 1950 until his retirement in 1955. It is impossible to think of Rideal away from a laboratory and so, even in his retirement, he will be found in a small group of laboratories, with an assistant or two, at Imperial College, London.

In his Sabatier lecture to the Society of Chemical Industry in 1943 Rideal suggested a mechanism of interaction between a van der Waals layer and a chemisorbed layer on surfaces. As the Rideal-Eley mechanism this theory has been competitive with that originally put forward by Langmuir, in which both reactants occupy competitively the chemisorbed layer. Later work of Rideal with Trapnell on evaporated tungsten films appears to favor the Langmuir concept but the two views are still much debated. The last five years of research have been as bewilderingly diversified as any of the periods in his active life which preceded it. Two or more generations of physical chemists now working in all the five continents testify to the breadth and range of his mind and the vitality which even physical disabili- ties or administrative difficulties could not quench. His life of service to physical chemical and colloid science has earned the gratitude that is written into these tributes from his friends. Ad multos annos.

HUGH TAYLOn April 7, 1956