H2O: A Biography of Water
by Philip Ball
Weidenfeld & Nicolson: 1999, 387pp.
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Review by Frank H. Stillinger
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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 Senior Editor at Nature, has undertaken. With the possible exception of gold, for no other substance could one write such an engaging account of the profound historical influence exerted on that wide range of activities. The author's panoramic knowledge conveyed through a clear and often delightful writing style has generated an attractive reading opportunity for a technically literate, but not necessarily expert, audience.
Philip Ball's narrative begins with the Big Bang and subsequent expansion of the Universe that in due course produced the elements, chemical compounds, and supplied the early Earth with a chemical and physical ambience that was conducive for spontaneous appearance of life. He traces our terrestrial geological chronology, and summarizes 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 conceivably might have spawned alternative life forms beyond Earth.
Although water has often been identified 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 upon freezing at ordinary pressures, and the presence of a liquid-phase density maximum at 4 degrees Celsius. 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 neighbors. The last 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 (Part II, entitled "Two Hands, Two Feet"). This representation serves to introduce the reader to the structure of ordinary hexagonal ice and the forms displayed by its snowflakes, and to the structures of high-pressure forms of ice.
The answer to the basic question-- What is liquid water?--through recorded history has reflected the emergence and maturing 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, say the last half century, considerable revision has occurred in the details of how the liquid geometrically is organized by hydrogen bonding. Imaginative, but now clearly naive, pictures insisted that water should be viewed as modified versions of ice ("iceberg" and "interstitial ice" models), as a "self clathrate", or as a distorted but everywhere fourfold-coordinated hydrogen bond network. The present consensus seems to have converged onto the perception of a macroscopic network with frequent strained and broken hydrogen bonds, permitting unbonded neighbors to occur in amounts varying 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, utilizing only molecular equations of motion and estimates of the fundamental intermolecular interactions, confirm the random defective network viewpoint while automatically producing the signature thermodynamic water anomalies. Quantitative modeling variations on this network viewpoint underlie recent studies directed at an intriguing possibility: Does the regime of supercooled liquid water harbor 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 internal to living organisms differs from its pure bulk form. Aqueous biofluids are electrolytes, and typically contain a wide array of biopolymers, nutrients, and metabolites. And as Philip Ball takes pains to stress to his readers, intracellular water is forced to occupy a very crowded neighborhood indeed, with available channels between its biopolymer space-competitors measured in nanometers, if not in Angstroms. Consequently most biological water is surface, or interfacial, water. Yet this aqueous solvent medium has the obligation to control the native folding patterns of proteins, and to act 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 the research frontier. In particular, the author provides an account of the present understanding of the so-called "hydrophobic interaction" phenomenon that contributes significantly to protein folding and to membrane structural stability by driving together hydrocarbon-like molecular moieties.
It is in connection with 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 with the diameter of human hair (p. 245). Using random samples from this reviewer's own head as a basis, the statement offered appears to be off by about two orders of magnitude.
Water as an object of research scrutiny arguably has attracted more than its share of questionable, even absurd, claims. Like it or not, these scraps of pathological science constitute a legitimate part of the biography of water. Detailed accounts for three notorious examples form the subject for Part IV, entitled "Strange Brew". They are the polywater episode that began in the former Soviet Union in the 1960's, "cold fusion" announced by Pons and Fleischmann in the U.S. in March 1989, and the alleged homeopathic phenomenon reported a year earlier by Jacques Benveniste and collaborators for repeatedly diluted solutions of anti-IgE antibodies. Perhaps inclusion of the last of these was inevitable, given that Nature itself was an active but nervous participant in its dissemination. Some might judge these and other less prominent water aberrations as detractions from the scientific legitimacy of the field, but the author intimates correctly that the situation deserves a more positive spin. First, these challenges to technical common sense stimulate responses that affirm the health and vigor of the scientific method as ordinarily construed. Second, occasional bizarre claims can be interpreted as far-out indicators that creative imagination is widely at play, which upon suitable filtration provides the driving force for progress.
Circumstances required reading this book for review while hurricane Floyd inflicted its epic watery damage on the Atlantic coastline of the U.S. This was a forceful reminder that understanding, let alone predicting, phenomena of all length scales in our water-rich environment is still woefully inadequate. The mind automatically wanders into musing about what a sequel to "H2O: A Biography of Water" written at the end of the next century might reveal that the present example cannot. But for now, Philip Ball's contribution is a delightful status report.
[Frank H. Stillinger is at Bell Laboratories, Lucent Technologies,
600 Mountain Avenue, Murray Hill, NJ 07974, USA]
