What struck me most about the ACS list, however, was first how it seemed to conflate ‘experiment’ with ‘discovery’ – the now pervasive paradigm for historical and philosophical discussions of scientific work. And, second, I noticed how ‘beautiful’ was often equated by the panellists with what one of them called ‘conceptual simplicity’, coupled to the lingering notion that a ‘beautiful’ experiment ought also to be an important one. Indeed, the editorial article accompanying the list defined beautiful in this instance as ‘elegantly simple but significant.’
Elegance and simplicity are surely among the key attributes that entitle an experiment to be labelled beautiful, and some of my selections have been made for that reason. But it is not at all clear that these should be the only, or even the principal, criteria for every selection. In fact, if there was ever any intention of that being so for the ACS list, it was flouted more than once. For example, William Perkin’s synthesis of aniline mauve, the first aniline dye, in 1856, which fetched in at number 5 in the final ranking, was as messy and inelegant an experiment as one could imagine: the dye was the initially unpromising residue produced by a wholly misconceived attempt at chemical synthesis (see page 154). But the colour itself was surely beautiful, and to my mind that counts for something – albeit not enough to win a place on my list.
As for the issue of significance: there is no real reason why we should demand that a beautiful experiment also be an important one. In practice, that consideration takes care of itself, however, since inevitably the experiments we tend to record and recall and analyse in sufficient detail to know what really happened are those that made an impact. So all of the examples I have chosen do have some broader significance in chemistry or in science more generally. But they are not chosen specifically for that reason, nor are they in any sense meant to represent milestones in the evolution of chemical thought or practice.
I hope I will have said enough by now to justify the position that regards ‘experiment’ as implying ‘experimental science’, which could involve a series of investigations, perhaps even spanning several years. This means, however, that compiling a list inevitably means comparing apples and oranges: how do you weigh a single, neat test of some hypothesis against a conclusion derived from the dedicated accumulation of data over a long period? The former can have the beauty of a dramatic revelation; the beauty of the latter can derive from the construction of a coherent chain of logical argument and deduction. For example, experiment number 3 on the ACS list, the determination by the German chemist Emil Fischer in the early 1890s of the precise three-dimensional structure of the glucose molecule, was, in the words of science historian Peter Ramberg,
part of a large research project involving several smaller projects on the classification of the natural monosaccharides [sugars] that gradually came together in 1891 . . . . There was therefore no one specific experiment that ‘determined’ the configuration of glucose. This would be an example perhaps of ‘beautiful chemical reasoning’, rather than a specific experiment.
The same is true of Antoine Lavoisier’s work on the oxidation of metals in the seventeenth century, which led him finally to his oxygen theory of combustion. It was a milestone in chemistry (see page 30), it was ranked number 2 in the ACS list – but I am afraid it seemed just too diffuse an endeavour even for me to regard as a single ‘experiment’.
Yet I have tried to take a very loose view of how one should regard both ‘beautiful’ and ‘experiment’. One of the key themes in all of the cases I have chosen is that they are shaped by human attributes: invention, elegance, perseverance, imagination, ingenuity. This has tended to work against the inclusion of experiments (like Perkin’s) whose success depended on serendipity: chance discoveries are appealing and entertaining, but I find it hard to see beauty in sheer good fortune. (Admittedly, however, most serendipity is more than that.) In retrospect, I realised that each of the selections I have made can be considered to exemplify a different factor that (without providing an exhaustive list) contributes to the beauty of an experiment, and I have suggested as much in my chapter titles.
In the end, I think there are two key reasons why an exercise like this one could be regarded as rather more than sheer indulgence in the current fad for making lists of ‘greats’ and ‘favourites’. One is that it encourages us to think about just what an experiment is and what role experiments play in the evolution of science. It seems absolutely clear that this role extends well beyond the traditional one of hypothesis-testing. Moreover, in researching the histories of some of these experiments I was made aware of the gap that sometimes exists between the popular notion of how they happened and what they meant, and (as far as it can be discerned at all) the historical reality. Experiments give a concrete framework on which to hang stories about the histories of science – but sometimes those stories come to have a strong element of invention about them, which in itself says something interesting about how we understand both science and history.
The second justification for the exercise is that there is nothing like a list to provoke comment and dissent – and thereby, one might hope, to stimulate debate about how science is practiced and about the goals that it sets for itself. I fully expect to be told how outrageous it is that I have omitted this or that experiment from my choices, or that I have included undeserving candidates. In fact, I look forward to it.
CHAPTER 1
How Does Your Garden Grow?
Van Helmont’s Willow Tree and the Beauty of Quantification
Vilvoorde, near Brussels, early 17th century—Jan Baptista van Helmont, a Flemish physician, demonstrates that everything tangible is ultimately made from water, by growing a willow tree in a pot of soil nourished by nothing but pure water. His identification of water as the ‘primal substance’ is consistent with the Biblical account of Creation and thus supports the Christian basis of van Helmont’s ‘chemical philosophy’. His ideas, published only after his death, represent the final flourish of a semi-mystical view of chemistry that was shortly to give way to the strictly mechanistic philosophy championed by René Descartes.
Perhaps the first thing school students of chemistry learn is that it is all about weighing things. So many grams of this added to so many grams of that: no wonder it so often seems like cookery.
There is nothing obvious about this need for quantification in the study of matter and its transformations. There is little evidence of it in the philosophies of ancient Greece, which sought to explain nature in terms of vague, qualitative propensities and tendencies, affinities and aversions. For Aristotle, things fell to earth because they possessed a natural ‘downward’ propensity. Empedocles claimed rather charmingly that the mixing and separation of his four elements to make all the bodies of the world were the result of the forces of ‘love’ and ‘strife’.
This is not to say, of course, that quantification was absent from the ancient world. Of course it wasn’t. How can you conduct trade unless you know what you are buying and selling? How can you plan a building without specifying the heights and proportions? Throughout the ancient cultures of the Middle and Near East, the cubit was the standard measure of length: the distance from the point of the elbow to the tip of the middle finger. The dimensions of Solomon’s Temple are listed in great detail in the Bible’s first Book of Kings: an illustration of how much quantification mattered in the court of ancient Israel. Double-pan balances are depicted in Egyptian wall paintings from around 2000 BC, and precious materials were weighed out in grains and shekels. (Because the number of grains to a shekel varied from one country to another, a merchant in the Mediterranean would have to carry several sets of standard stone weights.)
And artisans knew that if you wanted to make some useful substance by ‘art’ – which is to say, by chemistry, which was then indistinguishable from alchemy – then you had to get the proportions right. A Mesopotamian recipe for glass, recorded in cuneiform script, specifies that one must heat together ‘sixty parts of sand, a hundred and eighty parts of ashes from sea plants [and] five parts chalk’. In Alexandria such prescriptions were collated and recorded in alchemical manuscripts,