Luck in the Lab Helped My Career

My scientific career has been helped along by two marvelous instances of good luck. The first occurred while I was a research student in chemistry at Leeds University where my supervisor was Prof. R. Whytlaw-Gray, the leader of a distinguished school for the measurement of atomic weights. His method depended on the use of a very delicate microbalance to determine the vapor densities of substances in their dilute gaseous states. The problem he gave me was to obtain a new and more precise value of the atomic weight of fluorine by measuring the vapor density of sulfur hexafluoride, a substance well-known for its inertness that is prepared by passing fluorine over powdered sulfur. After getting my fluorine-generating cell to work properly I made liter upon liter of SF6, which I stored in evacuated flasks. The subsequent purification of the gas was carried out in a vacuum apparatus and consisted, in the first place, in the removal of lower fluorides of sulfur, such as S2F2, by passing the gas over the liquid alloy of sodium and potassium, and secondly by repeated condensation of the SF6 to its solid state, followed by hard pumping to remove traces of air. Every time I allowed the SF6 to re-evaporate into storage flasks I noticed a tiny drop of liquid remaining behind. Was it water that had somehow escaped the treatment with Na/K? Out of curiosity I evaporated it into the microbalance part of my apparatus and was positively thrilled to find that its vapor density corresponded to a molecular weight of 254—dead on for S2F10. Whytlaw-Gray was as excited as I was to think that the department could claim the discovery of a new gas! He straight away came to my basement room and went through the process of vapor density measurement himself, using a different microbalance. He confirmed that the molecular weight was indeed 254 and this led to our announcement in Nature (vol. 131, p. 763) in 1933. My further program of work was then switched to that of a chemical analysis of the new gas (to make doubly sure) together with an investigation of its physical properties. No doubt I should still have gained a Ph.D. even if S2F10 hadn’t existed. Even so, it provided a nice start to my scientific career. My second stroke of good luck occurred during World War II and was of much greater significance. At that time I was the scientist in charge of RDX research and development at the Royal Ordnance Factory at Bridgwater. RDX, also known as cyclonite, was a newly produced explosive made by the nitration of hexamine (hexamethylene tetramine) with concentrated nitric acid. It had not previously been manufactured by large-scale continuous process. Indeed, the laboratory studies prior to the Bridgwater plant’s being designed and brought into operation had mainly consisted of batchwise nitrations in beakers. The highest reaction yields obtained in the hatchwise reaction, where finely divided hexamine was added to stirred acid, was about 80 percent (i.e., 1 mole of hexamine gave 0.8 mole of RDX), the remaining 20 percent being wasted in side reactions. What was very unsatisfactory when the continuously operating Bridgwater plant came into operation early in the war was that the yield was considerably less than 80 percent. It was my good fortune to discover that the reason resided in a significant chemical distinction between hatch reaction and the continuous reaction that had been adopted. Later this led to my making a very general study of the theory of continuous and steady state reaction, with applications to living cells as well as to the chemical industry. The essential point was really very simple. The continuous nitration vessel had been designed in the form of what I later called a CSTR, a continuous stirred tank reactor. The acid and the hexamine were fed separately into a vigorously stirred tank and the natural consequence of this mixing was that the concentration of acid within the reactor was the same as its concentration in the outflow, and was thus much lower than its concentration in the feed. Laboratory studies had established that the yield of RDX diminished rapidly with the increasing dilution of the acid. Also, the reaction was found to be very fast. Thus, whereas the yield obtained in a stirred beaker in the lab was the integral over a sequence of diminishing instantaneous yields, each of them characteristic of the momentary acid concentration, the steady state yield- obtained from the CSTR was that which was characteristic of the “spent” acid in the outflow. Having established this theory it was not difficult to devise a modification to the plant that resulted in an appreciably higher yield of RDX. This had the useful effect of increasing the output of the explosive at a critical period of the war. For me personally it was a marvelous instance of good fortune. During my weekends, away from the ROF, I slogged away at developing the theory of continuous reaction processes, making distinction between the performance of tubular reactors and continuous stirred tank reactors. Although I remained at the Royal Ordnance Factory until the end of the war, the ministry allowed me to publish my first paper on the subject (in Transactions of the Faraday Society, vol. 40, p. 352, 1944) as if from Southampton University, from where I had been seconded during hostilities. My only subsequent regret was that this paper failed to make mention, due to my lack of literature-searching facilities, of an earlier publication by McMullin and Weber which had discussed the bypassing effects in a CSTR. After the war I published several more papers on continuous reactor theory and these, I think, were helpful in stimulating this new field of chemical engineering. Previously chemical engineering had developed mainly to meet the needs of the petroleum industry, and was largely concerned with processes such as distillation, gas absorption and so on. “Chemical reaction engineering,” as it became known, was a new branch, and its arrival gave rise to a spate of publications from many authors. For myself, I became particularly taken up with the concept of the living cell’s being itself a continuous reactor. Perhaps the chemical industry might learn from this something about how the cell succeeds in producing such a marvelous range of chemicals without requiring either high temperatures or high pressures. But that is another story. So much for my good luck. As we know, when there are independent chances, the likelihood of a further “lucky” one is unchanged even if two have occurred already. So I am still hoping for a third! "Can there ever be anything new in the world?” asked Denbigh in his book An Inventive Universe—and answered the deceptively simple question with “a cautious yes.”As implied by the titles of this and other popular philosophical works, and of his major texts such as The Thermodynamics of the Steady State and The Principles of Chemical Equilibrium, Denbigh has long been preoccupied by “time’s arrow” and the concepts of entropy and thermodynamics. Formerly professor of chemical engineering science at London University and of chemical technology at the University of Edinburgh, Denbigh is now a visiting research fellow at King’s College, London. During World War II. he put his knowledge of thermodynamics at the disposal of the Ministry of Supply (Explosives), before resuming his academic career at Cambridge. From 1977 to 1983 he was director of the Council for Science and Society, reflecting his deep interest in the social relations of science.

Luck in the Lab Helped My Career

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