Dmitry Mendeleev: Playing cards with atoms
M.V.N. Murthy, The Institute of Mathematical Sciences, Chennai

Higgs boson particle is in the news these days. We hear that with the discovery of Higgs particles we have completed the discovery of all the basic fundamental building blocks whose properties and interactions complete what is called the Standard Model of Particle Physics. What we have achieved today is the completion of the ``periodic table of fundamental particles". Is this the end of the story? We do not know yet, but the history of science teaches us not to close our books---be open and be skeptical.
Nearly about 150 years ago yet another ``standard model" of fundamental particles was completed---well almost. These fundamental particles were called atoms in those days and there were many. It was called the Periodic Table of Atoms and the man who did it, yes almost single handedly, went by the name Dmitry Mendeleev, a chemist born in Siberia (1834-1907). He completed the quest which began with Democritus in Greece and took the first giant step towards understanding the properties of matter.

The laughing philosopher
Our story of Mendeleev has to begin with Democritus, born in Abdera in Greece some time around 460 BC. He was popularly known as the laughing philosopher since he was a fun loving guy. He is supposed to have traveled widely including to far off places such as India and Egypt. He was not exactly popular with his famous contemporaries like Plato and Aristotle who seem to have disapproved of his ideas.
But he was more a scientist than a philosopher. He is supposed to have said ``Nothing exists except atoms and space (or void); everything else is opinion".  The name atom has its origins in the Greek word ``atomos" (a=not+tomos=divisible, meaning indivisible) used by Democritus and revived in 1805 by British chemist John Dalton. (Shown is a 1628 painting of Democritus by Hendrik ter Brugghen. Source: wikipedia).
Democritus held the view that everything is made up of atoms which are indivisible. He thought there may be many different types of atoms coming in a variety of shapes and sizes. But if we only have objects with indivisible atoms arranged together, you cannot break or even cut such an object and further no motion is possible. In response to this criticism, Democritus introduced the idea of void or space, or vacuum in modern language, which allows the atoms to wiggle around to make motion possible. 
The notion of vacuum is almost akin to introducing the concept of zero in the theory of numbers. It is really nothing, but its presence is necessary in order to make the connection between indivisible atoms and the structure of matter. The notion of space between atoms is as close as we can get to the modern notion of the structure of matter.
Democritus was ignored by by the dominant Greek philosophers like Plato and Aristotle. We know about Democritus' ideas only through quotations from later Greek historians. Nevertheless, the idea of the atom was put in cold storage for a very very long time for nearly 2000 years. Only recently was it revived by the physicists Galileo and later Sir Isaac Newton, in the 17th century. Later the chemists took over and refined the idea of the atom, leading to the periodic table of atoms. So now we fast forward to Newton from Democritus.

Discovery of nothing
Isaac Newton, in particular, subscribed to the idea of corpuscles or particles of matter. He wrote " ... it seems probable to me that God in the Beginning formed matter in solid, massy, hard impenetrable moveable particles...". He also thought that these are so hard that they never wear out or break in pieces, the hardness of the whole arises from the hardness of the parts.
We might guess that Democritus would have approved of Newton and said, these particles are my atoms. Newton also extended this notion to light, forming the basis of his corpuscular theory.  These ideas, though based indirectly on experimental facts, are in fact theoretical just like those of Democritus. 
To prove Democritus' ideas you not only have to prove the existence of atoms but also show that there is empty space between them. The christian church all along insisted that nature abhors vacuum. This followed the ideas of Aristotle who opposed the idea of vacuum during the time of Democritus.
It was up to Evangelista Toricelli, a student of Galileo, to prove the that there can be ``nothing". He poured mercury into a tube filling it completely, closed both ends and put the tube into a bowl containing mercury and removed the stopper at the bottom. Some of the mercury flowed out, but much remained in a column. At the top of the tube was however ``nothing". Well, not really nothing, but almost that---he had created a vacuum where the pressure was about a billionth of normal atmospheric pressure.
Even today this is how you measure atmospheric pressure, through the barometer first invented by Toricelli. In a sense Toricelli was trying out the main idea of Democritus---there are fundamental particles--atoms--and space (nothing) between them. You can move the atoms using pressure and leave nothing behind!! So through Toricelli we have the first experimental attempt, moving beyond ideas and theory, at proving the existence of atoms. 
Around the same time, Torricelli's experiments were put on a firm footing by Robert Boyle. Using mercury and air columns, he showed that increasing pressure reduces the volume in direct proportion. We call this the Boyle's law, it is one of the most important discoveries used by scientists extensively in analysing properties of gases.
While squeezing gas was possible, what about liquids and solids? No, problem, since you assume there is much less of ``nothing" in liquids and and even less in solids. Still, Boyle, who preferred to call the atoms corpuscles, had problems convincing his contemporaries in the 17th century who were still rooted in the Aristotelean universe of continuous matter.  

Phlogiston to Oxygen
There remains some thing more---what are these atoms? How many types are there? Democritus had only vague ideas about what types of atoms are there and how they combine. We need to do better. It was left to the chemists to complete this job.
Until the Frenchman Antoine-Laurent de Lavoisier came on the scene in the 18th century (1743-1794), chemistry was not yet a quantitative science. Various beliefs were in existence about the content of matter: people thought the fundamental elements were air, earth, water, fire. In ancient India space was also added to this to make up five fundamental elements.
Later, some early chemists speculated on such fundamental elements such as salt, mercury, sulfur, oil, spirit, acid, phlegm, etc., which were expected to be present in all compounds. Burning was attributed to a fire-like object called ``phlogiston" which was supposed to be present in all combustible objects and released during combustion in the form of fire. It was a complex situation with no percieved order.
A large amount of credit for putting chemistry on a quantative basis goes to Lavoisier.  Apart from chemistry he is credited with establishing the metric system. By his time there was a lot of unorganised data on what we today call chemical reactions, which he set about to organise. He recognised the role of oxygen in combustion, the rusting of metal, as well as in animal and plant respiration. He made accurate mass measurements of reactants and products in a chemical reaction and showed that even though the state of the matter may change in a chemical reaction, the total mass of the matter before and after every chemical change remains the same. He created the ``chemical balance" which he used expertly in his work. 
Lavoisier played with gases extensively; he was the first to split water into hydrogen and oxygen (found to be always in the ratio 1:2) and also produced water by mixing hydrogen and oxygen in the correct proportion of two parts of hydrogen with one part of oxygen.  He also investigated the composition of air to prove that it was primarily a mixture of nitrogen and oxygen. A sketch of his lab (from the Musée densities Arts et Métiers, Paris, France) is shown (source: Wikipedia).
Lavoisier introduced the modern nomenclature of chemistry-- names like oxide, sulfide, nitrous, etc-- which helped catalogue a large number of compounds with the names themselves carrying sufficient information about the compounds. Essentially he brought some order to the chaotic system of naming in chemistry during his time. He is remembered today for putting chemistry as science on par with physics as an exact science in the 18th century.
Unfortunately Lavoisier's life was cut short when he was executed at the age of 50 during the ``Reign of Terror in France" .  This was the period following the French revolution when many nobelmen were branded as traitors and guillotined. Lavoisier was in fact a liberal and an early supporter of the revolution, but he had intervened on behalf of a number of foreign scientists including the famous mathematician and astronomer Joseph Louis Lagrange and so became unpopular with the revolutionists. 
Upon his execution Lagrange commented '' it took them only an instant to cut off his head, but France may not produce another such head in a century."
Nevertheless, Lavoisier did not think in terms of atoms. That was left to John Dalton, an Englishman, after whom followed various other scientists before Mendeleev finally completely solved the puzzle. This second part of this story will appear in the next issue of JM.