Cadmium sulfide (the solution has a much deeper, brilliant yellow color)
Freeman Dyson who is a hero of mine and who I have had the privilege of meeting at length several times is someone who has done a lot of interesting things during a long and fruitful life. Not only has he made brilliant, foundational contributions to many areas of mathematics, physics, engineering and astronomy but he has also written books showcasing elegant, wide-ranging, poetic prose.
If you look at Dyson's astonishingly diverse writings or talks it is easy to mistake him as a philosopher of science, a big picture thinker striding on the widest possible canvas.
But as he himself said to me during a long, one-on-one, intellectually sparkling lunch discussion last year, a lot of people think that talking about the big picture automatically makes one a philosopher. Dyson has indeed written about an amazing variety of big picture topics, from the origins of life to the colonization of space. But he also maintains that he has always been first and foremost a problem solver, someone who is much more interested in details than in grand theorizing. Whatever philosophy he manages to weave is built on a foundation of solving specific technical problems. This is partly evidenced by his work on highly technical engineering projects ranging from nuclear spaceships to nuclear reactors.
This quality would make Dyson quite comfortable in the company of chemists, since chemistry by its very nature is more a problem-solving discipline rather than a philosophical pursuit like cosmology or evolutionary biology. I was curious to know Dyson’s views on chemistry since while he has had thoughts on almost every imaginable topic, I could not really find anything by him on chemistry except for a review in Physics Today of Nobel Laureate Roald Hoffmann’s fine book “The Same and Not the Same”.
Then I remembered an excellent collection of interviews with Dyson that I found a few years ago on a website called Web of Stories. This website is a must-see for history of science enthusiasts. It features interviews with scores of famous scientists, humanists and artists from diverse disciplines. These interviews are real gems. The best thing about them is that they are long and detailed instead of two minute sound bytes; each interview lasts in total for several hours and covers most significant events in the interviewees’s life, so you get a real feel for the life and work of leading thinkers. In one of Dyson’s interviews I was delighted to find this:
“I was going to say about chemistry that Roald Hoffmann whom I got to know quite recently, who is a chemist who writes poetry and is a great character, he has the same attitude toward chemistry that I do. I mean it is the beauty of the details rather than any over-arching theory. In that way it’s very different from physics, and I had a taste for it. My taste is always more for the details than for the big picture…
…I learned chemistry from Christopher Longuet-Higgins who was already much more of an expert and more excited about chemistry than Eric James (Dyson’s chemistry teacher at Winchester College). And I remember Christopher bringing to Winchester some crystals of stannic iodide which he had made, which is the most marvelous stuff. It is a brilliant scarlet colour and it makes these beautiful scarlet crystals, and they’re also extremely heavy. If you have a little bottle full of it, it feels like lead. So that kind of chemistry I found delightful, just the sort of details of the actual stuff, rather than the theory that lay behind it.
I remember the joy when, here in Princeton, Willard Libby came on a visit once and brought along another little bottle of chemicals, which also was very heavy, and that was barium xenate, which was barium xenon oxide, which of course was an absolute revelation because nobody imagined that xenon could have compounds, being an inert gas. And it was sometime in the 1950s these compounds were discovered, and barium xenate is just such an ordinary stuff. It’s a sort of heavy white crystals which are completely stable, they don’t show any signs of anything strange and there it is. If you heat them up of course the xenon comes bubbling off…”
So there, I think Dyson would have felt right at home as a chemist. Chemists revel in solving particular problems. It’s not that they don’t care about general principles. Every once in a while someone like Linus Pauling or Alfred Werner comes along and ties together disparate threads into a neat superstructure. But the vast majority of chemical work consists of celebrating the diversity of structure and function inherent in natural and synthetic molecules. The point Dyson makes is an obvious and important one that is often lost among the clichéd caricatures of chemists bubbling frothy liquids and crystallizing colorful solids that one often sees in literature and cinema. But it’s precisely these bubbling liquids and colorful solids that endow chemistry with a palpable reality that’s often missing from more theoretical sciences.
A personal digression. I remember an episode from an undergraduate chemistry lab where we were supposed to estimate two unknown metal ions from a solution. After trying out every test in the book we could only detect copper. The other ion remained a mystery and we finally threw up our hands. That’s when the instructor revealed his trick. It turns out that the method of copper estimation that we were using involved turning the solution highly acidic with hydrochloric acid. With a smile on his face, the instructor put a single drop of the concentrated acidic solution in a large flask and then filled the flask to the brim with water, diluting the initial solution by at least a factor of ten thousand. Our eyes were glued to the flask as he passed hydrogen sulfide gas into the solution. And then, starting from the bottom and rising to the top, the flask filled up with the most beautiful yellow color that I have ever seen; it’s a sight that I will never forget. What happens is that cadmium is precipitated as cadmium sulfide only in dilute acidic solutions while for copper it’s the opposite. All our tests for detecting copper in concentrated acid missed the hidden cadmium, until it was ready to be unmasked by simple dilution.
Every chemist is familiar with this feeling of discovering something unknown, no matter how trivial or important, that actually exists; all the better if it has a brilliant scarlet or full-throated yellow color, as is often the case in chemistry. Dyson is right that there is something unmistakably reassuring, in-your-face - real – about holding a vial of something that was previously considered impossible.
The great organic chemist Robert Burns Woodward spoke of this very real quality of chemistry that helped him choose between chemistry and mathematics when he was a teenager:
“The fact is that I have always been very fond of mathematics- for one short period, I even toyed with the possibility of abandoning chemistry in its favour. I enjoyed immensely both its conceptual and formal beauties, and the precision and elegance of its relationships and transformations. Why then did I not succumb to its charms? For two reasons, I believe:
FIRST, because by and large, mathematics lacks the sensuous elements which play so large a role in my attraction to chemistry. I love crystals, the beauty of their form- and their formation; liquids, dormant, distilling, sloshing!; the fumes; the odors- good and bad; the rainbow of colours; the gleaming vessels, of every size, shape and purpose. Much as I might think about chemistry, it would not exist for me without these physical, visual, tangible, sensuous things.
SECOND, while in mathematics, presumably one’s imagination may run riot without limit, in chemistry, one’s ideas, however beautiful, logical, elegant, imaginative they may be in their own right, are simply without value unless they are actually applicable to the one physical environment we have- in short, they are only good if they work! I personally very much enjoy the very special challenge which this physical restraint on fantasy presents”
Woodward’s second reason for studying chemistry goes to the heart of the nature of empirical science, what Richard Feynman called “imagination in a straitjacket”. It’s a philosophy that drives all of science including the most rarefied theoretical ideas. Physicists often like to tell the story of how Einstein felt that “something had snapped inside” him when he saw the predictions of general relativity confirmed by observations of the perihelion of mercury. He surely must have felt the rare, once-in-a-lifetime satisfaction of a great theoretical construct being validated by a real observation that could be boiled down to a single number. We tend to think of Einstein as the great scientist-philosopher, but there he was, being ecstatic about a technical detail that was a crucial part of his magnum opus. Observing barium xenate or precipitating cadmium is not quite as momentous as confirming the theory of relativity, but I can readily imagine feeling a shiver down my spine if I had been presented with that sort of chemical evidence. Evidence that seemed to defy the impossible but which I could nonetheless hold in my hand and keep in my closet. That’s the joy of chemistry.
This is an updated version of a previous post on Scientific American.