Triple the pressure, and the volume shrank to a third, and so on. This effect became known as Boyle's law, a staple of chemistry to this day.
More important is a stunning implication of this experiment: air, or any gas, can be compressed. One way to understand this is to think of the gas as composed of particles separated by empty space. Under pressure, the particles are pushed closer together. Does this prove that atoms exist? Unfortunately, other explanations can be imagined, and Boyle's experiment only provided evidence consistent with the idea of atomism. The evidence was strong enough, however, to help convince Isaac Newton, among others, that an atomic theory of matter was the way to go. Boyle's compression experiment at the very least challenged the Aristotelian assumption that matter was continuous. There remained the problem of liquids and solids, which could not be squeezed with the same ease as gases. This didn't mean they aren't composed of atoms, just that they have less empty space.
Boyle was a champion of experimentation, which, despite the feats of Galileo and others, was still viewed with suspicion in the seventeenth century. Boyle carried on a long debate with Benedict Spinoza, the Dutch philosopher (and lens grinder), over the question of whether experiment could provide proof. To Spinoza only logical thought was proof; experiment was simply a tool for confirming or refuting an idea. Such great scientists as Huygens and Leibniz also doubted the value of experiment. Experimenters have always had an uphill battle.
Boyle's efforts to prove the existence of atoms (he preferred the term "corpuscles") advanced the science of chemistry, which was in a bit of a mess at the time. The prevailing belief of the day was still the old idea of elements, going back to the air, earth, fire, and water of Empedocles and modified through the years to include salt, sulfur, mercury, phlegm (phlegm?), oil, spirit, acid, and alkali. By the seventeenth century these were not just the simplest substances comprising matter according to the prevailing theory, they were believed to be the essential ingredients of everything. Acid, to take one example, was expected to be present in every compound. How confused chemists must have been! With these criteria even the simplest chemical reaction must have been impossible to analyze. Boyle's corpuscles led the way to a more reductionist, and simpler, method of analyzing compounds.
THE NAME GAME
One of the problems faced by chemists in the seventeenth and eighteenth centuries was that the names given to various chemicals made no sense. Antoine-Laurent Lavoisier (1743–1794) changed all that in 1787 with his classic work, Méthode de Nomenclature Chimique. Lavoisier could be called the Isaac Newton of chemistry. (Perhaps chemists call Newton the Lavoisier of physics.)
He was an amazing character. An accomplished geologist, Lavoisier was also a pioneer in scientific agriculture, an able financier, and a social reformer who had a hand in fomenting the French Revolution. He established a new system of weights and measures that led to the metric system, in use today in civilized nations. (In the 1990s the United States, not to be left too far behind, is inching toward the metric system.)
The previous century had produced a mountain of data, but they were hopelessly disorganized. The names of substances—pomph-olyx, colcothar, butter of arsenic, flowers of zinc, orpiment, martial ethiop—were colorful, but gave no clue to an underlying order. One of Lavoisier's mentors once told him, "The art of reasoning is nothing more than a language well arranged," and Lavoisier took this to heart. The Frenchman eventually shouldered the task of rearranging and renaming all of chemistry. He changed martial ethiop to iron oxide; orpiment became arsenic sulfide. The various prefixes, like "ox" and "sulf," and suffixes, like "ide" and "ous," helped organize and catalogue the countless numbers of compounds. What's in a name? Sometimes nomenclature is destiny. Would Archibald Leach have gotten all those movie roles if he hadn't changed his name to Cary Grant?
It wasn't quite that simple for Lavoisier. Before revising the nomenclature, he had to revise chemical theory itself. Lavoisier's major contributions to chemistry had to do with the nature of gases and the nature of combustion. Eighteenth-century chemists believed that if you heated water, you transmuted it to air, which they believed was the only true gas. Lavoisier's studies led to the first realization that any given element could exist in three states: solid, liquid, and "vapor." He also determined that the act of combustion was a chemical reaction in which substances such as carbon, sulfur, and phosphorus combined with oxygen. He displaced the theory of phlogiston, an Aristotelian-like obstacle to a true understanding of chemical reactions. More than this, Lavoisier's style of research—based on precision, exquisite experimental technique, and critical analysis of the assembled data—set chemistry on its modern course. Although Lavoisier's direct contribution to atomism was minor, without his groundwork scientists in the following century could not have discovered the first direct proof of the existence of atoms.
THE PELICAN AND THE BALLOON
Lavoisier was fascinated with water. At the time, many scientists were still convinced that water was a basic element, one that could not be split into smaller components. Some also believed in transmutation, thinking that water could be transmuted into earth, among other things. There were experiments to back this up. If you boil a pot of water long enough, eventually a solid residue will form on the surface. That's water being transmuted into another element, these scientists would say. Even the great Robert Boyle believed in transmutation. He had done experiments showing that plants grow by soaking up water. Ergo, water is transformed into stems, leaves, flowers, and so on. You can see why so many people distrusted experiment. Such conclusions are enough to make you start agreeing with Spinoza.
Lavoisier saw that the flaw in these experiments was one of measurement. He conducted his own experiment by boiling distilled water in a special vessel called a pelican. The pelican was so designed that the water vapor produced by boiling was trapped and condensed in a spherical cap, from which it returned to the boiling pot through two handlelike tubes. In this way no water was lost. Lavoisier carefully weighed the pelican and the distilled water, then boiled the water for 101 days. The long experiment produced an appreciable amount of solid residue. Lavoisier then weighed each element: the pelican, the water and the residue. The water weighed exactly the same after 101 days of boiling, which tells us something about Lavoisier's meticulous technique. The pelican, however weighed slightly less. The weight of the residue was equal to the weight lost by the vessel. Therefore the residue in the boiling water was not transmuted water but dissolved glass, silica, from the pelican. Lavoisier had shown that experimentation without precise measurement is worthless, even misleading. Lavoisier's chemical balance was his violin; he played it to revolutionize chemistry.
So much for transmutation. But many people, Lavoisier included, still believed water was a basic element. Lavoisier ended that illusion when he invented an apparatus with a double nozzle. He would shoot a different gas through each nozzle, hoping they would combine and form a third substance. One day he decided to work with oxygen and hydrogen, expecting them to mix together into some kind of acid. What he got was water. He described it as "pure as distilled water." Why not? He was making it from scratch. Obviously, water was not an element but a substance that could be manufactured from two parts hydrogen, one part oxygen.
In 1783 a historical event occurred that would indirectly further chemistry. The Montgolfier brothers demonstrated the first manned air flights with hot-air balloons. Soon thereafter J. A. C. Charles, a physics teacher no less, rose to a height of 10,000 feet in a balloon filled with hydrogen. Lavoisier was impressed; he saw in such balloons the possibility of rising above the clouds to study meteors. Soon thereafter he was named to a committee to explore methods of cheaply producing gas for the balloons. Lavoisier set up a large-scale operation to produce hydrogen by decomposing water into its constituent parts by percolating it through a gun barrel filled with hot iron rings.
At this point, no one with any sense still believed that water was an element. But there was a b
igger surprise for Lavoisier. He was splitting apart water now in vast quantities, and the numbers always came out the same. Water yielded oxygen and hydrogen in a weight ratio of eight to one every time. Clearly, some sort of neat mechanism was at work here, a mechanism that might be explained by an argument based on atoms.
Lavoisier did not speculate much about atomism, except to say that simple indivisible particles are at work in chemistry and we don't know much about them. Of course, he never had the opportunity to sit back in retirement and write his memoirs, in which he might have elaborated further on atoms. An early supporter of the Revolution, Lavoisier fell out of favor during the Reign of Terror and was sent to the guillotine in 1794 at the age of fifty.
The day after Lavoisier's execution, the geometer Joseph Louis Lagrange summed up the tragedy: "It took them only an instant to cut off that head, and a hundred years may not produce another like it."
BACK TO THE ATOM
The implications of Lavoisier's work were investigated a generation later by a modest, middle-class English schoolteacher named John Daiton (1766–1844). In Dalton we have at last our made-for-TV-movie image of a scientist. He appears to have led a totally uneventful private life and never married, saying that "my head is too full of triangles, chemical processes, and electrical experiments, etcetera, to think much of marriage." A big day for him was a walking tour and maybe attendance at a Quaker meeting.
Dalton started out as a humble teacher in a boarding school, where he filled his spare hours reading the works of Newton and Boyle. He put in over a decade at this job before landing a position as a professor of mathematics at a college in Manchester. When he arrived he was informed that he would also have to teach chemistry. He complained about twenty-one hours of teaching per week! In 1800 he resigned to open his own teaching academy, which gave him the time to pursue his chemical research. Until he unveiled his atomic theory of matter shortly after the turn of the century (between 1803 and 1808), Dalton was still considered little more than an amateur in the scientific community. As far as we know, Dalton was the first to formally resurrect Democritus's term atom to mean the tiny indivisible particles that make up matter. There was a difference, however. Recall that Democritus said atoms of different substances had different shapes. In Dalton's scheme, weight played the crucial role.
Dalton's atomic theory was his most important contribution. Whether it was "in the air" (it was) or whether history gives far too much credit to Dalton (as some historians say), no one questions the tremendous influence of the atomic theory on chemistry, a discipline that soon became one of the most pervasively influential sciences. That the first experimental "proof" of the reality of atoms came from chemistry is also most appropriate. Remember the ancient Greek passion: to see an unchanging "arche" in a world in which change is everywhere. The a-tom resolved the crisis. By rearranging a-toms, one can create all the change one wants, but the rock of our existence, the a-tom, is immutable. In chemistry, a relatively small number of atoms provide enormous choice because of the possible combinations: the carbon atom with one oxygen atom or two, hydrogen with oxygen, or chlorine or sulfur and so on. Yet the atoms of hydrogen are always hydrogen—identical one to another, immutable. But here we go, forgetting our hero Dalton.
Dalton, noting that the properties of gases can best be explained by postulating atoms, applied this idea to chemical reactions. He noticed that a chemical compound always contains the same weights of its constituent elements. For example, carbon and oxygen combine to form carbon monoxide (CO). To make CO, one always needs 12 grams of carbon and 16 grams of oxygen, or 12 pounds of carbon and 16 pounds of oxygen. Whatever units you use, the ratio is always 12 to 16. What can the explanation be? If one atom of carbon weighs 12 units and one atom of oxygen weighs 16 units, then the macroscopic weights of carbon and oxygen that disappear into CO will have this same ratio. This alone would be a weak argument for atoms. However; when you make hydrogen-oxygen compounds and hydrogen-carbon compounds, the relative weights of hydrogen, carbon, and oxygen are always 1 to 12 to 16. One begins to run out of alternative explanations. When the same logic is applied to many dozen compounds, atoms become the only sensible conclusion.
Dalton revolutionized science by declaring that the atom is the basic unit of the chemical element and that each chemical atom has its own weight. Here he is, writing in 1808:
There are three distinctions in the kinds of bodies, or three states, which have more specially claimed the attention of philosophical chemists; namely, those which are marked by the terms elastic fluids, liquids, and solids. A very famous instance is exhibited to us in water, of a body, which, in certain circumstances, is capable of assuming all three states. In steam we recognize a perfectly elastic fluid, in water a perfect liquid, and in ice a complete solid. These observations have tacitly led to the conclusion which seems universally adopted, that all bodies of sensible magnitude, whether liquid or solid, are constituted of a vast number of extremely small particles, or atoms of matter bound together by a force of attraction, which is more or less powerful according to circumstances....
Chemical analysis and synthesis go no farther than to organize the separation of particles one from another and their reunion. No new creation or destruction of matter is within the reach of chemical agency. We might as well attempt to introduce a new planet into the solar system, or to annihilate one already in existence, as to create or destroy a particle of hydrogen. All the changes we can produce consist in separating particles that are in a state of cohesion or combination, and joining those that were previously at a distance.
The contrast between Lavoisier and Dalton in scientific styles is interesting. Lavoisier was a meticulous measurer. He insisted on precision, and this paid off in a dramatic restructuring of chemical methodology. Dalton had many things wrong. He used 7 instead of 8 for the relative weight of oxygen to hydrogen. He had the composition of water and ammonia wrong. Nevertheless, he made one of the profound scientific discoveries of the age: after some 2,200 years of speculation and vague hypothesis, Dalton established the reality of atoms. He presented a new view which, "if established, as I doubt not it will in time, will produce the most important changes in the system of chemistry and reduce the whole to a science of great simplicity." His apparatus was not a powerful microscope, not a particle accelerator but some test tubes, a chemical balance, the chemical literature of his day, and creative inspiration.
What Dalton called an atom was certainly not the a-tom that Democritus envisioned. We now know that an oxygen atom, for example, is not indivisible. It has a complex substructure. But the name stuck: what we commonly call an atom today is Dalton's atom. It's a chemical atom, a single unit of a chemical element, such as hydrogen, oxygen, carbon, or uranium.
***
Headline in the Royal Enquirer in 1815:
CHEMIST FINDS ULTIMATE PARTICLE, ABANDONS BOA CONSTRICTORS, URINE
Once in a blue moon a scientist comes along who makes an observation that is so simple and elegant that it just has to be right, an observation that appears to solve, in one swift stroke, a problem that has tormented science for thousands of years. Once in a hundred blue moons the scientist is actually right.
All you can say about William Prout is that he came very close. Prout put forward one of the great "almost correct" guesses of his century. His guess was rejected for the wrong reasons and by the fickle finger of fate. Around 1815 this English chemist thought he had found the particle from which all matter was made. It was the hydrogen atom.
To be fair, it was a profound, elegant idea, albeit "slightly" wrong. Prout was doing what a good scientist does: looking for simplicity, in the Greek tradition. He was looking for a common denominator among the twenty-five known chemical elements at the time. Frankly, Prout was a bit out of his field. To his contemporaries, his main accomplishment was writing the definitive textbook on urine. He also conducted extensive experiments with boa constrictor excrement. How this led him to atomism, I don't care to
speculate.
Prout knew that hydrogen, with an atomic weight of 1, was the lightest of all the known elements. Maybe, said Prout, hydrogen is the "primary matter" and all the other elements are simply combinations of hydrogens. In the spirit of the ancients, he named this quintessence "protyle." His idea made a lot of sense, because the atomic weights of most of the elements were close to integers, multiples of the weight of hydrogen. The reason for this was that relative weights were then typically inaccurate. As the precision of atomic weights improved, the Prout hypothesis was crushed (for the wrong reason). Chlorine, for example, was found to have a relative weight of 35.5. That blew away Prout's concept because you can't have half an atom. We now know that natural chlorine is a mixture of two varieties, or isotopes. One has 35 "hydrogens" and the other has 37 "hydrogens." These "hydrogens" are really neutrons and protons, which have almost the same mass.
What Prout had really hypothesized was the existence of the nucleon (either of the particles, the proton or the neutron, that make up the nucleus) as the building block of atoms. It was a hell of a good try by Prout. The drive for a system simpler than the set of twenty-five or so elements was destined to succeed.
Not in the nineteenth century, however.
PLAYING CARDS WITH THE ELEMENTS
We end our breakneck jaunt through two hundred-plus years of chemistry with Dmitri Mendeleev (1834–1907), the Siberian-born chemist responsible for the periodic table of the elements. The table was an enormous step forward in classification and at the same time constituted progress in the search for Democritus's atom.
The God Particle Page 15