by John Carey
Mendeléeff was clear-visioned enough not to fall into such a pit. He took sixty-three cards and placed on them the names and properties of the elements. These cards he pinned on the walls of his laboratory. Then he carefully re-examined the data. He sorted out the similar elements and pinned their cards together again on the walls. A striking relationship was thus made clear.
Mendeléeff now arranged the elements into seven groups, starting with lithium (at. wt. 7), and followed by beryllium (at. wt. 9), boron (11), carbon (12), nitrogen (14), oxygen (16) and fluorine (19). The next element in the order of increasing atomic weight was sodium (23). This element resembled lithium very closely in both physical and chemical properties. He therefore placed it below lithium in his table. After placing five more elements he came to chlorine, which had properties very similiar to fluorine, under which it miraculously fell in his list. In this way he continued to arrange the remainder of the elements. When his list was completed he noticed a most remarkable order. How beautifully the elements fitted into their places! The very active metals lithium, sodium, potassium, rubidium and caesium fell into one group (No. 1). The extremely active non-metals, fluorine, chlorine, bromine and iodine, all appeared in the seventh group.
Mendeléeff had discovered that the properties of the elements ‘were periodic functions of their atomic weights,’ that is, their properties repeated themselves periodically after each seven elements. What a simple law he had discovered! But here was another astonishing fact. All the elements in Group I united with oxygen two atoms to one. All the atoms of the second group united with oxygen atom for atom. The elements in Group III joined with oxygen two atoms to three. Similar uniformities prevailed in the remaining groups of elements. What in the realm of nature could be more simple? To know the properties of one element of a certain group was to know, in a general way, the properties of all the elements in that group. What a saving of time and effort for his chemistry students!
Could his table be nothing but a strange coincidence? Mendeléeff wondered. He studied the properties of even the rarest of the elements. He re-searched the chemical literature lest he had, in the ardor of his work, misplaced an element to fit in with his beautiful edifice. Yes, here was a mistake! He had misplaced iodine, whose atomic weight was recorded as 127, and tellurium, 128, to agree with his scheme of things. Mendeléeff looked at his Periodic Table of the Elements and saw that it was good. With the courage of a prophet he made bold to say that the atomic weight of tellurium was wrong; that it must be between 123 and 126 and not 128, as its discoverer had determined. Here was downright heresy, but Dmitri was not afraid to buck the established order of things. For the present, he placed the element tellurium in its proper position, but with its false atomic weight. Years later his action was upheld, for further chemical discoveries proved his position of tellurium to be correct. This was one of the most magnificent prognostications in chemical history.
Perhaps Mendeléeff’s table was now free from flaws. Again he examined it, and once more he detected an apparent contradiction. Here was gold with the accepted atomic weight of 196.2 placed in a space which rightfully belonged to platinum, whose established atomic weight was 196.7. The fault-finders got busy. They pointed out this discrepancy with scorn. Mendeléeff made brave enough to claim that the figures of the analysts, and not his table, were inaccurate. He told them to wait. He would be vindicated. And again the balance of the chemist came to the aid of the philosopher, for the then-accepted weights were wrong and Mendeléeff was again right. Gold had an atomic weight greater than platinum. This table of the queer Russian was almost uncanny in its accuracy!
Mendeléeff was still to strike his greatest bolt. Here were places in his table which were vacant. Were they always to remain empty or had the efforts of man failed as yet to uncover some missing elements which belonged in these spaces? A less intrepid person would have shrunk from the conclusion that this Russian drew. Not this Tartar, who would not cut his hair even to please his Majesty, Czar Alexander III. He was convinced of the truth of his great generalization, and did not fear the blind, chemical sceptics.
Here in Group III was a gap between calcium and titanium. Since it occurred under boron, the missing element must resemble boron. This was his eka-boron which he predicted. There was another gap in the same group under aluminium. This element must resemble aluminium, so he called it eka-aluminium. And finally he found another vacant space between arsenic and eka-aluminium, which appeared in the fourth group. Since its position was below the element silicon, he called it eka-silicon. Thus he predicted three undiscovered elements and left it to his chemical contemporaries to verify his prophecies. Not such remarkable guesses after all – at least not to the genius Mendeléeff!
In 1869 Mendeléeff, before the Russian Chemical Society, presented his paper On the Relation of the Properties to the Atomic Weights of the Elements. In a vivid style he told them of his epoch-making conclusions. The whole scientific world was overwhelmed. His great discovery, however, had not sprung forth overnight full grown. The germ of this important law had begun to develop years before. Mendeléeff admitted that ‘the law was the direct outcome of the stock of generalizations of established facts which had accumulated by the end of the decade 1860–1870.’ De Chancourtois in France, Strecher in Germany, Newlands in England, and Cooke in America had noticed similarities among the properties of certain elements. But no better example could be cited of how two men, working independently in different countries, can arrive at the same generalization, than the case of Lothar Meyer, who conceived the Periodic Law at almost the same time as Mendeléeff. In 1870 there appeared in Liebig’s Annalen a table of the elements by Lothar Meyer which was almost identical with that of the Russian. The time was ripe for this great law. Some wanted the boldness or the genius necessary ‘to place the whole question at such a height that its reflection on the facts could be clearly seen.’ This was the statement of Mendeléeff himself. Enough elements had been discovered and studied to make possible the arrangement of a table such as Mendeléeff had prepared. Had Dmitri been born a generation before, he could never, in 1840, have enunicated the Periodic Law.
‘The Periodic Law has given to chemistry that prophetic power long regarded as the peculiar dignity of the sister science, astronomy.’ So wrote the American scientist Bolton. Mendeléeff had made places for more than sixty-three elements in his Table. Three more he had predicted. What of the other missing building blocks of the universe? Twenty-five years after the publication of Mendeléeff’s Table, two Englishmen, following a clue of Cavendish, came upon a new group of elements of which even the Russian had never dreamed. These elements constituted a queer company – the Zero Group as it was later named. Its members, seven in number, are the most unsociable of all the elements. Even with that ideal mixer, potassium, they will normally not unite. Fluorine, most violent of all the non-metals, cannot shake these hermit elements out of their inertness. Moissan tried sparking them with fluorine but failed to make them combine. (Xenon tetrafluoride and several other ‘noble’ compounds were prepared in 1962. They are no longer regarded as non-reactive.) Besides, they are all gases, invisible and odorless. Small wonder they had remained so long hidden.
True, the first of these noble gases, as they were called, had been observed in the sun’s chromosphere during a solar eclipse in August, 1868, but as nothing was known about it except its orange yellow spectral line, Mendeléeff did not even include it in his table. Later, Hillebrand described a gas expelled from cleveite. He knew enough about it to state that it differed from nitrogen but he failed to detect its real nature. Then Ramsay, obtaining a sample of the same mineral, bottled the gas expelled from it in a vacuum tube, sparked it and detected the spectral line of helium. The following year Kayser announced the presence of this gas in very minute amounts, one part in 185,000, in the earth’s atmosphere.
The story of the discovery and isolation of these gases from the air is one of the most amazing examples of precise and pa
instaking researches in the whole history of science. Ramsay had been casually introduced to chemistry while convalescing from an injury received in a football game. He had picked up a textbook in chemistry and turned to the description of the manufacture of gunpowder. This was his first lesson in chemistry. Rayleigh, his co-worker, had been urged to enter either the ministry or politics, and when he claimed that he owed a duty to science, was told his action was a lapse from the straight and narrow path. Such were the initiations of these two Englishmen into the science which brought them undying fame. They worked with gases so small in volume that it is difficult to understand how they could have studied them in their time. Rayleigh, in 1894, wrote to Lady Frances Balfour: ‘The new gas has been leading me a life. I had only about a quarter of a thimbleful. I now have a more decent quantity but it has cost about a thousand times its weight in gold. It has not yet been christened. One pundit suggested “aeron,” but when I have tried the effect privately, the answer has usually been, “When may we expect Moses?”’ It was finally christened argon, and if not Moses, there came other close relatives: neon, krypton, xenon and finally radon. These gases were isolated by Ramsay and Travers from one hundred and twenty tons of air which had been liquefied. Sir William Ramsay used a micro-balance which could detect a difference in weight of one fourteen-trillionth of an ounce. He worked with a millionth of a gram of invisible, gaseous radon – the size of a tenth of a pin’s head.
Besides these six Zero Group elements, some of which are doing effective work in argon and neon incandescent lamps, in helium-filled dirigibles, in electric signs, and in replacing the nitrogen in compressed air to prevent the ‘bends’ among caisson workers, seventeen other elements were unearthed. So that, a year after Mendeléeff died in 1907, eighty-six elements were listed in the Periodic Table, a fourfold increase since the days of Lavoisier …
To the end, Mendeléeff clung to scientific speculations. He published an attempt towards a chemical conception of the ether. He tried to solve the mystery of this intangible something which was believed to pervade the whole universe. To him ether was material, belonged to the zero Group of Elements, and consisted of particles a million times smaller than the atoms of hydrogen.
Two years after he was laid beside the grave of his mother and son, the American Pattison Muir declared that ‘the future will decide whether the Periodic Law is the long looked for goal, or only a stage in the journey: a resting place while material is gathered for the next advance.’ Had Mendeléeff lived a few more years, he would have witnessed the beginnings of the final development of his Periodic Table by a young Englishman at Manchester [Henry Mosely, who discovered the Law of Atomic Numbers, and was killed at Gallipoli in 1915 aged twenty-six].
The Russian peasant of his day never heard of the Periodic Law, but he remembered Dmitri Mendeléeff for another reason. One day, to photograph a solar eclipse, he shot into the air in a balloon, ‘flew on a bubble and pierced the sky.’ But to every boy and girl of the Soviet Union today Mendeléeff is a national hero. A special Mendeléeff stamp in his honor was issued in 1957 on the fiftieth anniversary of his death, and a new transuranium element, Number 101, created in 1955, was named mendelevium to commemorate his classic contribution to the science of chemistry.
Source: Bernard Jaffe, Crucibles: The Story of Chemistry from Ancient Alchemy to Nuclear Fission, new and revised updated fourth edition, New York, Dover Publications, 1976.
Socialism and Bacteria
The great French chemist and microbiologist Louis Pasteur (1822–95) established that putrefaction and fermentation are caused by micro-organisms. He introduced vaccination when he showed, in 1881, that sheep and cows vaccinated with the baccilli of anthrax became immune to the disease. ‘Pasteurization’, the heat-treatment of milk to destroy bacteria, such as those of tuberculosis, typhoid and brucellosis, was his invention. This account is from David Bodanis’s Web of Words (1988). The ‘Maxwell’ to whom he refers is James Clerk Maxwell (see p. 167), whose kinetic theory explained that the pressure of a gas is due to the incessant impacts of the gas molecules on the walls of the container.
It was dinner time in the Pasteur house, and Louis was at it again. With his wife, daughters and sole son sitting in mortified silence around the table; with the usual dinner guest, Monsieur Loir, at the table with them; with the best tablecloth laid, the right plates out, the first course on, and the long-suffering maids in position at the side; with everyone set to begin the meal, the Professor began his hunt.
‘He minutely inspected the bread that was served to him’, Monsieur Loir wrote much later, in old age, ‘and placed on the tablecloth everything he found in it: small fragments of wool, of cockroaches, of flour worms … I tried to find in my own piece of bread from the same load the objects found by Pasteur, but could not discover anything. All the others ate the same bread without finding anything in it.’
Then Pasteur went to work on the glasses. He lifted them up, peered at them closely, and wiped down each one he was going to use, hoping to remove all the contaminating dirt, which again no one else could see. He kept his fingers clean for the wiping, by refusing to shake hands with strangers or even friends during the day. The family waited, the maids and guest waited too, for all were used to the great man’s obsession. ‘This search took place at almost every meal’, Loir continued, ‘and is perhaps the most extraordinary memory that I have of Pasteur.’
What ever was going on? Had Pasteur gone bonkers, nuts, off his rocker? At first it’s tempting to think so. If Mme Pasteur came home from the Galeries Lafayette and started tearing apart the family’s food in search of non-existent wool and cockroaches, so that when her children returned they found her on the floor, legs out, hat askew and surrounded by great mounds of food in the kitchen, we could imagine that they would consider seeking professional help. But when it was their father who embarrassed them with his hunt through the food they took it as normal. To some extent this was because he was the greatest scientist in France, and so had the prerogatives of the gifted. But I suspect even more important was that this pre-dinner hunting ritual matched almost exactly what Pasteur talked about when it was over and he finally looked up.
There are many accounts surviving of what personal conversation with Pasteur was like. In his loud voice, and with his sombre expression (there is only one known drawing, photo, engraving, or sculpture of Pasteur smiling), Pasteur would continually harp on two themes. The first of course was his laboratory work. During dinner at home he would recount with great satisfaction details of the mice he had eviscerated that day, or the purées of vaccinated spinal cord he had prepared, or whatever else he had done in his continuing, remorseless battle against the bacteria. Those bacteria were tiny infecting creatures that most people couldn’t see, but which were always there, ready to pounce, to enter us and take over and grow. The hunt inside the dinner bread was no aberration with them around.
After the account of the day’s laboratory work had run dry, Pasteur’s monotone would turn to his second topic: politics. It was the only interest he held as strongly as bacteria. Some of his views were shared with all Frenchmen of his time, such as his great hatred of Germany, especially after the invasion of 1870–1. It was so strong that he devoted months of free work to the perfecting of French beer, so loyal patriots wouldn’t have to drink that Boche muck again. Yet his main political view was not quite so universally shared. Pasteur was an extreme reactionary in politics. He ran (unsuccessfully) for the Senate on an extreme right-wing ticket, and in his letters recorded that the social high point of his life was a one-week visit with Louis Napoleon, at the Emperor’s Palace in Compiègne.
The reason was simple. Pasteur had a horror of democracy. There was ordered society, which was good, especially if led by a strong man, and there was also a curious anti-society, a disordered thing of raw uncultivated bodies: the mob. That was a collection of small infecting creatures that decent people didn’t ordinarily see, but which was always there, ready to poun
ce, to enter our society and take over and grow. It was what Pasteur and most right-wing Frenchmen thought had created the French Revolution, surging into existence on the streets of Paris; it was what had produced the Terror against the aristocracy, and the uprisings of 1830, 1848, and then – what Pasteur called a saturnale – the brief workers’ takeover of the Commune in 1871.
Would someone coming late to the table know which of his two enemies Pasteur was going on about? The language of Pasteur and conservatives generally against the masses of the people was almost exactly like the language Pasteur had developed to use against bacteria. Both were everywhere, small swarming things ready to strike, to grow and propagate. They would destroy us in doing so, subvert our inner structure, have us collapse in disorder, and turn us into – the worst of all possible fates – a thing no different from the seething mass that had attacked. Let the mob take Paris and without the King or Emperor to shore us up we would dissolve into aimless bodies no different from the mob; let the bacterial mob take our physical body and we would decay into a putrefying bacterial mass no different from the attackers here either. If unpleasant entities such as the people or bacteria had to exist, then they must be kept firmly in their place. The people, and especially the workers, were safe only if kept in passive Catholic trade unions, or state-run clubs, or other trustworthy bureaucratic bounds. The bacteria, in all their unpleasant and quick-to-grow varieties, were safe only if restricted to one slot in the Great Chain of Being, that of the decomposer of dead bodies, destroying order only after all life in it had naturally gone, and returning its atoms to the soil for rebirth. Outside of that, though, and they were terrible.