H2O: A Biography of Water

  • Philip Ball
Weidenfeld & Nicolson: 1999. 387 pp. £17.99
Dewdrops: a macroscopic network of molecules linked by frequent but transient hydrogen bonds. Credit: CORBIS/GEORGE LEPP

Linking human perceptions of water in mythology, cosmology, politics, literature and the physical and biological sciences (and pseudosciences) may seem to be an idiosyncratic objective. Yet that is just what Philip Ball, until recently a senior editor at Nature, has undertaken. With the possible exception of gold, there can be no other substance for which one could write such an engaging account of the profound historical influence exerted on this wide range of subjects. The author's panoramic knowledge, conveyed through a clear and often delightful writing style, makes attractive reading for a technically literate, but not necessarily expert, audience.

The narrative begins with the Big Bang and the subsequent expansion of the Universe that, in due course, produced the elements and chemical compounds, and supplied the early Earth with a chemical and physical ambience conducive to the spontaneous appearance of life. Ball traces our terrestrial geological chronology, and summarizes our present understanding of the role of continental, atmospheric and oceanic water transport in present-day meteorology. And in keeping with the burgeoning interest in planetary exploration in our Solar System, he summarizes the intriguing extraterrestrial evidence for water in both solid and liquid forms that might conceivably have spawned alternative life forms beyond Earth.

Although water has often been seen as ‘unique’ among liquids, labelling it as such is not especially informative, except in the most trivial sense. Nevertheless, it exhibits an impressive array of anomalies in its physical properties that might qualify it as ‘eccentric’. Among these anomalies are the well-known expansion when it freezes at ordinary pressures, and the presence of a liquid-phase density maximum at 4°C.

The author undertakes to explain, or at least to rationalize, these attributes in terms of the known structure of the water molecule, its resulting electrical asymmetry, and its propensity to engage in tetrahedral arrangements of hydrogen bonds with its own kind as neighbours. The last of these has been amusingly anthropomorphized with line drawings that should appeal to all ages: each water molecule has been rendered as a round-bodied elf whose two arms are destined to grab nearby elfin ankles. This device is used to introduce the reader to the structure of ordinary hexagonal ice and the forms displayed by snowflakes, and to the structures of high-pressure forms of ice.

In answering the question ‘What is liquid water?’ by looking at history, Ball has reflected the emergence and maturation of science itself. Beginning with the ancient Greek perception of the substance as one of the primal elements, the shifting answer has reflected specifically the rise of modern structural chemistry. But even in what one might call the ‘modern’ period (the past half-century, say), considerable revision has occurred to the details of how the liquid is geometrically organized by hydrogen bonding. Imaginative, but now clearly naive, pictures insisted that water should be viewed as modified versions of ice (the ‘iceberg’ and ‘interstitial ice’ models), as a ‘self clathrate’, or as a distorted four-fold coordinated network of hydrogen bonds.

The present consensus seems to be that liquid water is a macroscopic network of molecules connected by frequent but transient hydrogen bonds, which allow unbonded neighbours to occur in numbers that vary with temperature and pressure. Attempts to identify unambiguous patterns of local molecular order that represent portions of the known ice polymorphs have generally proved to be unproductive. In any case, several independent computer simulations for liquid water, using only molecular equations of motion and estimates of the fundamental intermolecular interactions, confirm the random, defective-network viewpoint while automatically producing the characteristic thermodynamic water anomalies.

Quantitative modelling variations on this network viewpoint underlie recent studies directed at an intriguing possibility: does the regime of supercooled liquid water harbour a hidden first-order phase transition between two metastable liquids with different densities (to which the term ‘polyamorphism’ has recently been attached), along with an associated second critical point?

Water that is internal to living organisms differs from its pure bulk form. Aqueous biological fluids are electrolytes, and typically contain a wide array of biopolymers, nutrients and metabolites. As Ball emphasizes, intracellular water is forced to occupy a very crowded neighbourhood indeed, with available channels between the biopolymers being measured in nanometres, if not in ångströms. Consequently, most biological water is surface, or interfacial, water. Yet this aqueous solvent medium has vital roles in controlling the native folding patterns of proteins, and acting as a lubricant for the entire dynamic apparatus of life.

Quantitative details of this solvation role are still a bit hazy, but some broad themes have emerged from research. In particular, Ball provides an account of the present understanding of the ‘hydrophobic interaction’ phenomenon, which contributes significantly to protein folding and to the structural stability of membranes by driving together hydrocarbon-like molecular moieties.

It is in connection with Ball's discussion of the interfacial properties of liquid water that I would raise a minor quibble with what otherwise appears to be an accurate text. This concerns the comparison of the range of hydrophobic surface effects to the diameter of human hair. By using random samples from my own head as a basis, I estimate that this statement appears to be out by about two orders of magnitude.

As an object of research scrutiny, water has arguably attracted more than its fair share of questionable, or even absurd, claims. But like it or not, these scraps of pathological science constitute a legitimate part of the biography of water, so Ball provides detailed accounts of three notorious examples: the ‘polywater’ episode, which began in the former Soviet Union in the 1960s; ‘cold fusion’, announced by Stanley Pons and Martin Fleischmann in the United States in March 1989; and the alleged homoeopathic phenomenon reported a year earlier by Jacques Benveniste and collaborators for repeatedly diluted solutions of anti-IgE antibodies. Perhaps the inclusion of the last of these was inevitable, given that Nature itself was an active but nervous participant in its dissemination.

Some might judge that these and other less prominent water aberrations detract from the scientific legitimacy of the field, but the author intimates correctly that the situation deserves a more positive spin. First, the responses to these challenges to technical common sense affirm the health and vigour of the scientific method. Second, occasional bizarre claims can be interpreted as far-out indicators that creative imagination is widely at play, and this, when suitably filtered, provides the driving force for progress.

I read this book while Hurricane Floyd was inflicting its epic watery damage on the Atlantic coastline of the United States. This was a forceful reminder that understanding, let alone predicting, phenomena of all scales in our water-rich environment is still woefully inadequate. The mind wanders into musing about what a sequel to this book written at the end of the next century might reveal that this volume cannot. But for now, Ball's contribution is a delightful status report.