A Summer Vacation

‘I will speak of the Whole,’said Democritus. But the infinitely little is the least obvious. —PASCAL,

I

SOME men — astronomers, cosmologists, world builders — take the universe as their province, and seek to comprehend the all in one inclusive system. Others — and perhaps they are the more ambitious — look closer. They peer into the atom, and try to read in the microcosm the eternal riddle of a world and a life and an intelligence. Irving Langmuir is of this latter group. He chose a trail into the infinitely little as his way of satisfying the great curiosity, and out of that highly specialized pursuit has come new light on familiar mysteries, a new understanding of fundamental phenomena, a whole new branch of science. New industries, new factories, new products, emerged from his findings — yet he had no practical end in view when he entered upon this research.

Indeed, the whole remarkable venture began as a summer vacation. Langmuir was a teacher of chemistry who varied the monotony of pedagogical tasks with summers of mountain climbing. In 1909, however, an opportunity opened to spend July and August in a research laboratory. The vacation then begun has continued more than twenty-four years, for he never went back to his classroom, but stayed on in the laboratory, fascinated by an experiment. It led to other experiments, and discovery followed discovery as he brilliantly pioneered new frontiers of knowledge, blazing ‘ paths where highways never ran,’ often a solitary figure, exploring, experiencing, satisfying his soul. From such preoccupations he was called to Stockholm last winter to receive the Nobel Prize in Chemistry.

II

A search of the Langmuir pedigree reveals no scientific forbears, unless we count a maternal grandfather who was a New England physician. Irving Langmuir’s father was a business man, self-made in the sense that he hired out as a clerk at the age of fourteen and by the time he was thirty-five had accumulated a comfortable fortune. Then, soon after the birth of his fourth son, he lost it all and more in a mining venture, and much of the remainder of his life was a period of financial struggle. During his last six years he was agency director for Europe of the New York Life Insurance Company; the European post gave the family advantages of travel and of cosmopolitan contacts; but the four boys grew up in this atmosphere of struggle, and it colored their life with a sense of serious purpose. There was Dean, the youngest; Irving, six years older; next, Charles Herbert, who was five years older than Irving; and the eldest, Arthur, whose study of chemistry was to turn Irving’s interest in that direction.

Perhaps the most definite tendency of science in the household was the disposition to record accurately and systematically whatever went on within the domain of the family. Charles Langmuir, the father, began a diary in his early manhood. He also kept a cashbook recording in double entry every day’s financial transactions, even to the purchase of a penny newspaper. He kept a separate record of his travels, the itinerary, the hotels visited, the number of the room he occupied. Sadie Comings Langmuir, the mother, was almost as keen as her husband for record keeping. She too treasured the day’s events in a diary, and instilled the habit in her sons. She encouraged them to write detailed accounts of their experiences and observations.

When he was eleven years old, living with an aunt in Brooklyn (his birthplace), Irving Langmuir wrote his mother, in Paris, of a project that was engaging his attention. The definiteness of the detail is characteristic: —

I am building a windmill which is going to be about 3 feet high and 1 foot wide at the bottom and 6 inches wide at the top. The wheel is going to be like this. [The letter contains a sketch.] The wheel’s axil is going to be made of wood with pieces of tin this shape [another sketch], each one being about 3 1/2 inches long. The whole wheel’s diameter will be about 8 ins. I have two sides all done and the other two sides half done of the tower part.

Within a year the family were settled in Paris, — the insurance company’s headquarters were there, — and soon after Irving’s thirteenth birthday Mrs. Langmuir was writing to a friend in America: —

Irving’s brain is working like an engine all the time, and it is wonderful to hear him talk with Herbert on scientific subjects. Herbert says he fairly has to shun electricity, for the child gets beside himself with enthusiasm, and shows such intelligence on the subject that it fairly scares him.

A tireless stoker of this scientific flame was Arthur, who had now completed undergraduate studies at Columbia and was entering Heidelberg for a postgraduate course in chemistry. There were many letters back and forth between the two. Irving, eager to try the experiments which his brother outlined, was delighted to have access to the laboratory of a small boarding school in a Paris suburb where he had been entered. One of the teachers encouraged the thirteen-year-old to use logarithms and to solve problems in trigonometry. He delighted in these extracurricular activities. But most of his time in the French school was spiritual torture to the sensitive boy. The absurdly rigorous discipline and the inflexible system of learning by rote stifled him. Until he was fourteen he ‘hated school, and did poorly at it,’ to quote his own recent estimate of that period.

In his fifteenth year he returned to America and entered school in Philadelphia. The following year Arthur, who was now starting out as an industrial chemist, married, and Irving came to live in his brother’s home while attending high school in Brooklyn. Here the boy taught himself the calculus. He knew so much chemistry that the school excused him from attending classes in the subject. He fitted up a laboratory at home and learned qualitative analysis under Arthur’s tutelage.

When Irving Langmuir enrolled in Columbia University, it was to become a candidate for the degree of metallurgical engineer, in its School of Mines, though he had no intention of practising metallurgy or mining. ‘But the course was strong in chemistry,’ he explains; ‘it had more physics than the chemical course, and more mathematics than the course in physics — and I wanted all three.’

Judged by usual collegiate standards, Langmuir’s four years at Columbia would be rated a failure. He ‘made’ no clubs or teams, took no part in athletics, never ‘went out’ for one of the university papers, was not invited to join a social fraternity or to serve on a class committee. Outside classrooms and laboratories, the teeming university seemingly was unaware of his existence.

The professors showed little intuitional ability to spot a future Nobel laureate. The intense, eager youth was never invited to any of the professorial homes for an evening’s chat. Dr. R. S. Woodward, professor of mechanics, one day posed this question to the class: ‘If you could do what you want most to do, what career would you choose?’ When the question came to Langmuir he answered, ‘I’d like to be situated like Lord Kelvin — free to do research as I wish.’ This touched some chord in the professor. He encouraged the ambitious junior to consult him; there were long talks between the two after class. ‘Professor Woodward suggested many interesting problems,’ recalls Langmuir, ‘which I loved to work out — for the fun of it.’ He was graduated in June 1903, with an average grade of 94 per cent.

The following fall the ‘metallurgical engineer’ enrolled at Gottingen for advanced studies in physical chemistry under Professor Walther Nernst. During the three ensuing postgraduate years in Germany there was considerable debate in the young scientist’s mind, and by letter between him and his brothers, as to his future. Should he go into chemistry commercially, or should he aim for the more rarefied heights of pure science? I am privileged to quote a letter he received at this time from his brother Charles Herbert: The whole matter resolves itself into the question whether you have, or have not, exceptional ability in pure science research. If you simply have a well-grounded knowledge and a thorough efficiency, you should certainly go right into the business of chemistry, where you can be of most use to yourself and everybody else. But if you are the exceptional man, it is, in my opinion, your duty to be one of the pioneer scholars in America. . . . The time has come when this country must have her distinctive scholars. If they do not get great honor now, they surely will by the time you have done anything particularly worthy. Meanwhile, you will have the incalculable advantage of a great aim with all that it contributes to happiness and the full life. . . .

There is a great deal that is noble and inspiring in business, and business can always be conducted in the better way, but it is a lower thing for some men than research and scholarship. Most of us are suited to nothing else but business, not being finely enough organized mentally to spend our careers in other than active work. But you perhaps are one of the few with creative brains. If you are (and don’t decide so unless you have good authority) you will betray your true self if you devote your life selfishly to private enterprises and personal acquisition. And the minute you allow yourself to deviate from the path of pure science, you will lose something in character, and more still in the power to aspire and the possibility to be truly happy.

This was in 1904. At that time no Nobel prize had come to any American, though in Europe more than a dozen scientists had received this supreme accolade. Just that year Lord Rayleigh had been named as the prize man in physics and Sir William Ramsay in chemistry, a double recognition of their joint discovery of argon — that strange rare gas which Langmuir was destined to harness to the purposes of man. Whether there entered the mind of the young American any thought of his own future in association with a Nobel prize, I do not know. But when he came home in 1906 he had decided to risk a career in scholarship, and had accepted appointment as instructor in chemistry at Stevens Institute of Technology, Hoboken, New Jersey.

It is interesting to speculate on the ‘ifs’ of the past. What might have been this man’s life if Columbia had discerned his latent powers, and had installed her brilliant unknown in line for one of her chairs in science? Or if Stevens had recognized the genius of research who was fiddling away his hours trying to teach sophomore engineers the rudiments of chemistry? He had a difficult time. Teaching, with its demand for a disciplinarian and its interminable piles of papers to be graded, was a chore. One remembers Whistler serving as draftsman in the Coast Survey office, and Charles Lamb poring over the ledgers of the London accountant.

With his brother Dean, Irving used to take long walks along the Palisades and into the Highlands of the Hudson, and the talks that enlivened these jaunts are forever memorable to the younger man. Usually the theme was some subject of science, frequently an interpretation of familiar phenomena. A rainbow, a raindrop, an oil film on a pond — these are worlds of beauty and orderliness to Irving Langmuir. I have seen him poise a soap bubble to point out its dark monomolecular area that exists for an instant just before the bubble bursts. How resonant his voice, how vibrant as he rises to some peak of exposition, like a mountain climber who has guided you up his favorite height to point out his favorite view.

He might have gone mountaineering again that summer of 1909 but for a meeting of a scientific society in Schenectady the previous autumn. Langmuir attended the meeting, and renewed acquaintance with a classmate of Columbia days, Dr. Colin G. Fink, who was then on the staff of the General Electric Laboratory in Schenectady. Industrial research was comparatively new in America; most scientists associated it with such pedestrian pursuits as tests and analyses; but as Dr. Fink conducted his friend through the Laboratory, introduced him to members of the staff and to their work, the visitor was enormously impressed and interested. Here was an authentic atmosphere of research, and every facility to delight the heart of an experimenter. When, a few months later, the suggestion came that he spend his vacation in the Laboratory, it was not difficult for Langmuir to accept.

III

Among the problems under scrutiny was one which we may call ‘the mystery of the lamp.’ The Laboratory had been trying to improve the incandescent lamp, and had been blocked by a certain ‘offsetting’ effect of the wire filament. Tungsten, which will endure more heat than any other solid, had been substituted for the earlier carbon and tantalum filaments, and the bulb had been exhausted of its air to an extent attained in no other laboratory; yet, after a few hundred hours of use, the tungsten became brittle, the filament crumbled, the lamp failed — and nobody knew why. Accidentally, three tungsten wires had been produced which gave fairly satisfactory results — but again, nobody knew why.

It occurred to Langmuir that there might be an impurity in the tungsten in the form of absorbed gases, and that these might be responsible for its unaccountable behavior. As his summer’s research he proposed to heat various samples of tungsten wire in high vacuum, and if any gases came off he would measure them. He set up his apparatus, obtained specimens of wire, installed one in a lamp, and attached a vacuum pump.

He got gas, plenty of it, and kept heating the wire and pumping the bulb until he had obtained an amount of gas equal to seven thousand times the volume of the filament. He was astonished. It was preposterous to assume that all this had been hidden within the hairlike strand of tungsten. Where did it come from? Langmuir spent all summer trailing the gases to their sources, and never did get back to his original project of investigating the samples of wire. ‘How much more logical it would have been,’ he remarked, ‘ if I had dropped the work as soon as it was evident that the method employed was not going to solve the problem of the brittleness of the wire.’

Curiosity led him on. ‘Frankly, I was not so much interested in trying to improve the lamps as in finding out the scientific principles underlying these peculiar effects.’

September arrived. The classroom in Hoboken was waiting, and here was its chemistry instructor in the midst of an engrossing experiment. The director of the Laboratory, Dr. W. R. Whitney, asked if he would care to stay. Langmuir was eager to stay, but his Scotch conscience made him protest that he could not foresee any practical issue from his research. ‘ I am merely curious about the mysterious phenomena that occur in these lamps.’ The discerning Dr. Whitney recognized the temperament. ‘ Go ahead; follow any line of inquiry you like; find out all you can of what goes on in a lamp.’

And Langmuir did. The work absorbed him. He was given first one assistant, then others, and thousands of dollars were made available to finance his flights into the vacuum. He continued to track down the ubiquitous gases to their lairs, and found that they came for the most part from the glass bulb. He continued to discover and record their varied behavior. He began to introduce other gases into the lamp, purposely to spoil the vacuum, to see what would happen. He worked in these ways nearly three years before any practical application was made of any of his results.

But he became intimately acquainted with the invisible world of colliding molecules and curiously individualistic atoms. A trace of nitrogen introduced into the vacuum behaved very differently from its usual inert self. Pure oxygen had its own atomic antics. And so with each gas. Hydrogen was the most fascinating actor of all, and presently Langmuir was concentrating his experiments on hydrogen. It lured him, as the North Pole had lured Peary, and nights and days he could think of nothing but the queer ways of hydrogen in a vacuum.

IV

He found, for example, that the presence of any gas in the lamp accelerated the loss of heat from the incandescent filament. This was expected, for the gas molecules coming in contact with the hot wire take up some of its energy, which quickens their motion, and they fly off at higher velocities to bang into other molecules or against the inner surface of the bulb. Langmuir was familiar with this thermal conduction of gases. It was a subject he had studied at Göttingen under Nernst; he had worked out curves to picture the increase of conduction with temperature. But earlier experiments had been with filaments of platinum, which melts at 3200 degrees Fahrenheit, and there were no data on performances at temperatures above 2000 degrees. Now he was working with the most refractory of all the elements, tungsten, which must be heated to 6200 degrees before it melts, and the experimenter was eager to see what would happen in the higher range thus opened up. He found that the ascending order of his curves continued with fair consistency for all gases — except hydrogen.

When hydrogen was introduced, and the electric current turned on, the rate of heat loss increased steadily until the glowing filament reached a temperature of 3600 degrees. Then the curve rose rapidly to a height five times as great as would be expected. Evidently, at these higher temperatures, something happened to hydrogen to make it a glutton for heat.

The hydrogen also staged a mysterious disappearing act. When a measured quantity of the gas was introduced into the lamp bulb, the pressure rose exactly as one would expect. But if you then turned the electric switch and lighted the lamp, the pressure slowly dropped to zero. The hydrogen had disappeared! More was introduced, and under like conditions it too disappeared until finally a stage was reached when the pressure remained constant.

But where had the hydrogen gone? The filament was suspect, but experiment soon exonerated it. The only hiding place left was the inner surface of the glass bulb. Langmuir put the lamp in an electric furnace and baked it, heated it until the glass was near melting. Then, at last, the lost hydrogen began to reappear. Like a swarm of leeches, its particles had attached themselves to the glass; and only the most drastic heat treatment could make them budge.

One more experiment, and the mystery was unmasked. Langmuir had introduced hydrogen, had lighted the lamp, and the hydrogen had dis-

appeared. His new experiment was to turn off the current, allow the filament to cool, and then to introduce a measured quantity of oxygen. Instantly the oxygen disappeared. Other additions of oxygen vanished too, until a point of saturation was reached. It was noticed that the amount of oxygen taken up was exactly the quantity required by the hydrogen to combine in the proportions of H20.

Everyone knows that two parts of hydrogen join with one part of oxygen to form water, but only the chemist knows what tremendous forces are required to effect this union. You might mix the two gases till doomsday, and nothing would happen until you gave the mixture some violent molecular blow, as by an electric spark, a ray of ultra-violet light, or some other packed quantum of energy.

But here in Langmuir’s experiment the union occurred spontaneously, in a cold lamp bulb, without any outside stimulus. Obviously the experience that had made hydrogen such a glutton for heat, that had caused it to swarm to the inner surface of the glass, had also endowed it with extraordinary affinity for oxygen. It could no longer be regarded as the familiar hydrogen of ordinary usage, a gas which exists in compact molecules of two atoms each. It must be different. It was different. And now Langmuir knew precisely what it was, and saw how it came to be.

The tumultuous heat of incandescent tungsten had split the hydrogen molecule in two.

The bursting of these bonds had drained enormous energy from the tungsten, as was indicated by the extraordinary heat loss.

These sundered halves of the hydrogen molecule, these separated atoms, with their natural affinities now loose and unsatisfied, were eager for any kind of union — with oxygen, if oxygen was to be had; if not, with the glass surface of the bulb.

Theory had predicted that, if hydrogen existed free in its atomic form, it should have these characteristics. And now Langmuir had discovered it. The demon within the lamp was atomic hydrogen!

V

I have sketched this pioneer research in some detail, because it is one of the fundamental explorations of the new chemicophysics, now our basic science. Fifty years from now men will look back to it as to a lofty landmark in the march of discovery, just as to-day we rate Faraday’s work with electromagnets as epochal. Mr. Gladstone, attending an early demonstration of the dynamo, was prompted to ask Faraday, ‘But what use is it?’ — a question which I believe Langmuir’s discovery was never challenged to answer. No, the alert engineers at Schenectady knew what they were after all the time, and were wise enough to see that this quiet searcher in the Laboratory, who was ‘merely curious about the mysterious phenomena that occur in these lamps,’ was getting somewhere — though they did not dream of the wealth of applications that would trail off from his pure science research. Four practical results are outstanding: —

1.First, better lamps. From his studies of the behavior of gases in the bulb, Langmuir learned that the vacuum was not the secret of lamp efficiency. Though the main effort of lamp makers up to his time had been concentrated on attaining higher vacua within the bulb, Langmuir showed that the fatal crumbling away of the tungsten did not occur when the filament was coiled in a certain way and when the bulb was filled with an inert gas, argon. The argon, by its gaseous pressure, prevented the filament from evaporating. By these and other innovations Langmuir halved the lamp’s consumption of electric current. According to statisticians who keep tabs on such economies, this improvement is yielding the American public an average nightly saving of $1,000,000 on its electric light bill.

2. His study of lamps led Langmuir to new methods of pumping vacua, and resulted in his invention of the mercury condensation pump. By means of a blast of hot mercury vapor, this Langmuir pump siphons air out of a container so rapidly that in five seconds a quart bulb is emptied to a hundredmillionth of an atmosphere. This means that in those five seconds the harnessed tornado of mercury jerks some 24,999,999 million million air molecules out of the bulb.

3. With his powerful pump Langmuir was able to attain degrees of emptiness far beyond any previously known, and these equipped him to penetrate still deeper into that world of the vacuum where radio communication has its home. He discovered the ‘space charge,’ now recognized as a fundamental principle of electronics. He found that an infinitesimal pinch of thorium added to the tungsten filament of a radio tube would speed up its flow of current a hundred thousand fold. By the summer of 1933, more than sixty patents had resulted from Langmuir’s studies, about half his patents being in the field of radio engineering.

4. One of the more spectacular inventions is the atomic hydrogen torch, used in welding the fine parts of machines. The idea for this industrial application came as a hunch. Dr. Langmuir was discussing some related matter, when suddenly it flashed in his mind that atomic hydrogen might be used to produce an intense flame. For, he reasoned, if the temperature of incandescent tungsten is required to tear the halves of the molecules apart, would not the broken molecules, if allowed to reunite, give up enormous heat in the process? The hunch was tried out; it worked; and to-day the highest steady temperature that man has been able to generate and control is that of the atomic hydrogen torch. Above 6800 degrees Fahrenheit has been registered.

But these practicalities are only the fringes of his achievement. The really significant outcome that resulted from the discovery of half a hydrogen molecule is its turning of attention to the chemical phenomena of surfaces. The Swedish Academy of Sciences, in its citation, declares that the Nobel Prize is awarded to Irving Langmuir ‘for pioneer work in surface chemistry.’ And here we are down to fundamentals. Surface chemistry represents a new and strategic attack on the hidden mechanism of nature.

VI

Forty years ago Lord Rayleigh was enticed by the iridescent films which oil makes on water, and began important studies of these familiar phenomena. Our own Willard Gibbs interested himself in soap bubbles, was led to consider what soap does to the surface of water, and from these inquiries worked out a mathematical formula accounting for the surface tension of liquids. Later Sir James Dewar investigated the tendency of certain gases to attach themselves to the surfaces of charcoal — knowledge that was put to practical use during the World War in the manufacture of gas masks. Dr. Langmuir, in his pursuit of the energetic hydrogen in the lamp, found that the gas attached itself to the inner surface of the glass bulb in a single layer of atoms.

This discovery of the monatomic film was a revolutionary finding, though Dr. Langmuir was looking for just such an arrangement. Prior to this the generally accepted idea among chemists was that when atoms were adsorbed, or attached to a surface, the concentration was densest at the surface and gradually thinned out with distance, like a miniature atmosphere. But here, in the case of hydrogen on glass, there was no hovering atmosphere — just one tightly held layer of atoms, and above that little attraction.

Langmuir explored other adsorbed films, and in every instance the film was one layer deep. In the case of carbon monoxide (a compound of one carbon atom united to one oxygen) the film was a single molecule thick — and here an interesting new detail showed itself: all of the molecules attached themselves to the surface with their carbon atoms down. It was as though the carbon end were the head, and alone had the power to bite into and hold on to the surface.

Oil films on water showed the same orientation. The oil spread in a layer exactly one molecule thick, and each molecule clung to the water in a uniform way. These oil molecules are large. Predominantly they are groups of hydrogen and carbon atoms, some being chains of fifteen to twenty-nine of these groups linked together. All are alike in one peculiarity: they have at the end of the chain an atom of oxygen coupled with an atom of hydrogen. In every oil film, Dr. Langmuir found, it was this OH end that attached the molecule to the water. It was the head. It was able to satisfy its own affinity for the water molecules, but was not strong enough to drag the long hydrocarbon chain down into the water.

In molecules of short chains it is able to do this; therefore such substances dissolve readily in water.

Alcohol is an example. Its hydrocarbon chain is only two atoms long, and the eager oxygen-hydrogen head is able to pull the whole molecule under.

All the soluble carbohydrates are strong in the OH group. Sugar, for example, may be called hydra-headed, since in every molecule there are several OH groups — eleven in the familiar cane sugar.

In contrast with these mixers is another class of oils which will have nothing to do with water. Pure mineral oil is an example; it will neither dissolve nor form a monomolecular film. Examine the make-up of its molecule and you find it different from the others in only one particular: it has no OH group. Bereft of a head, the molecules are neutral to surfaces, and so hold themselves apart in inhospitable globules.

These peculiarities of the infinitely little absorbed Langmuir. For months his laboratory was cluttered up with trays of water alive with invisible films. He began to measure the molecules. In the case of stearic acid, a principal ingredient of candle tallow, he found that the length of the molecule is about one ten-millionth of an inch, its width about one fifth as much. Other oils showed slenderer units. He visualized the oil film as made up of billions of long waving molecules, like eel grass in a swamp, each a snakelike structure of linked atoms attached to the water by its active head.

As oil after oil was studied, various shapes showed up. The molecule of olive oil measured about the same in length as in thickness. A surface film of olive oil suggests more the appearance of a field of cabbages than of eel grass. The castor-oil molecule showed an even more striking departure, for its height above the surface is only about a third of its diameter, giving the molecule the appearance of a disk. This is explained as an effect of its abundance of heads, for each molecule has not only three active OH groups at one end, but six additional ones on its sides; the affinity of the nine groups for water causes the molecule to lie flat on its side. As a result, the castor-oil film is exceedingly thin; it measures only one hundredmillionth of an inch.

VII

These studies led Langmuir into a curious flatland. The adsorbed molecules could move about on the surface, but were unable to rise above or dive beneath it. Their actions constituted a chemistry confined to two dimensions. One day, in his laboratory, I watched him fill a tray with water and then touch the water surface with the tip of a needle that had been dipped in an oil (myristic acid). The oil spread over the water as a film. Tests showed that its particles were in continual agitation, like the colliding molecules of a gas; indeed, the oil film was a two-dimensional gas which could move about freely in flatland, but apparently was unaware of the third dimension.

Langmuir demonstrated this. He laid a strip of paper across the water surface, and by pushing the strip forced the oil to one end of the tray. If the agitated particles had any freedom to leave the surface, they surely would have used it. Instead, under the pressure of the paper barrier, the film condensed into a two-dimensional film of liquid. Further pressure converted it into a two-dimensional solid. The thin crust, measuring only one twenty-millionth of an inch in thickness, was invisible, but by blowing on the surface one could prove its rigidity. On the release of the barrier the pressure dropped, and instantly the two-dimensional solid melted into a two-dimensional liquid, which in turn evaporated into a two-dimensional gas and diffused over the surface, as the freed molecules darted about in wild abandon. Why they had allowed themselves to be squeezed into solidity seems an amazing bit of chemical perversity — until one knows the eagerness of the molecular head for water. The OH group has an affinity.

This affinity is responsible for many characteristics of water itself: not only does the OH head of the oil molecule have an avidity for water, but the OH head of the water molecule has an enormous avidity for the oil. The three atoms of the water molecule, H2O, are arranged in the sequence HOH. Thus both its ends are heads; on either side it presents an active group to its fellows. The mutual attraction of these molecular heads holds the liquid together, gives its surface a strong ‘skin’ which enables insects to walk on water, causes particles of water to gang together into large drops, and endows the fluid with a high boiling point which distillers and other professional separators find useful. These and other characteristics are accounted for by the predominance of the OH group.

To test this, destroy the OH group. It can be done by removing the oxygen atom from water. What is left is two hydrogen atoms, HH, which pair off as a single molecule of hydrogen. Normally the stuff is a gas, but by sufficiently lowering the temperature it can be reduced to liquid, and then hydrogen may be compared, quality for quality, with water. Striking contrasts show up.

Hydrogen Water
(HH) (HOH)
Boiling point —423° F. +212° F.
Surface energy 5 units 118 units
Molecular volume 47 30

Note that hydrogen has very little surface energy. This means that its surface tension is slight, therefore it has a weak ‘skin’; when it is poured or spilled, it forms minute drops; attraction between its molecules is so feeble that at a temperature of 423 degrees below zero the hydrogen boils. This behavior is at the opposite extreme from that of water — and yet, the only fundamental difference between a hydrogen molecule and a water molecule is the absence of one oxygen atom in the hydrogen. By adding an O to the HH, we make it possible for the molecule to develop an OH complex. The influence of that masterful combine gives the water molecule such compactness that its volume shrinks to about two thirds that of the hydrogen molecule; and it gives to all the water molecules such affinity for one another that the surface energy is increased above that of liquid hydrogen twentythree fold, and the boiling point is raised by 635 degrees.

This tenacity crops up all through nature. It explains many curious contrasts. Ethane, for example, one of the constituents of illuminating gas, differs in structure from alcohol by the trifle of a single atom. But what a difference in characteristics!

Ethane

H H

H-C-C-H boils at 120° below zero F.

H H

Alcohol

H H

H-C-C-O-H boils at 173° above zero F.

H H

Ethane presents to the world an unbroken shell of hydrogen atoms, and it behaves much as hydrogen does. But add a single oxygen atom, and the upset is enormous. The effect is to break through the hydrogen and provide the molecule with an OH head. Ethane changes to alcohol, the boiling point is raised from minus 120 degrees to plus 173 degrees — and the tenacious OH group is the little giant that does it.

From such minutiae Langmuir was led to formulate his Principle of Independent Surface Action, now recognized as a primary law of the new chemistry. It sees the compound molecule as a piece of architecture. Each group of atoms within the molecule has its individual surface characteristics. An OH surface is different from an H surface, just as a sun porch is different from a windowless wall; and so with other groups. Dr. Langmuir found that he could predict molecular behavior by this principle. Also, by the same rule, from a study of behavior he could forecast structure.

Surface chemistry thus assumes a primary rôle in science. In the architectural surfaces of the molecules and of the atoms lies the explanation of the strange affinities and lack of affinities which bind and loose the physical world.

VIII

Through knowledge of these differences in the infinitely little has come the ability to manipulate many surface phenomena to man’s advantage. Not only better lamps and more sensitive radio tubes, but also such practicalities as tough-skinned lubricants for airplane motors and other high-speed machines, improved flotation methods of extracting metals from ores, the production of artificial fertilizers for agriculture, even the application of antitoxins and serums to the human system, are derived directly from the propensity of certain atoms and molecules to arrange themselves on surfaces in single-layer films. The vital processes of the living cell, the means by which protoplasm protects itself against a hostile world and spins its mysterious texture of life, appear to be largely a mechanics of monomolecular layers. Surface chemistry is not only fundamental chemistry; it may be fundamental biology. Hardly a week passes that Langmuir does not receive a letter from some biologist, cancer specialist, or other medical researcher, reporting some monomolecular-film phenomenon discovered in the life processes.

But Langmuir holds his own researches to the realm of the unit particles, that fascinating borderland of chemistry and physics where one science passes almost imperceptibly into the other — frontier country. He has acquired a technique in working with these infinitesimals that may be suggested by a brief reference to his recent experiments with cæsium. This is a rare metal of a silver-yellow color, so fusible that the heat of one’s hand is sufficient to cause it to melt; when vaporized particles of cæsium are released in a glass bulb containing a tungsten filament, they perform antics which have proved extremely useful in fundamental studies of surface phenomena. Langmuir has devised an apparatus so sensitive that if there is but a single cæsium atom within a space of one cubic yard the device can detect it.

One atom in a cubic yard? An engineer in the laboratory explained. Suppose, to make the proportions comprehensible, we enlarge the cubic yard of air to a globe the size of the earth. On the same scale the air molecules may be represented as flies speeding about at high velocities and frequently colliding. Assuming the air in the cubic yard to be at atmospheric pressure, there would be about 700 flies to every cubic foot of the hollow earth. If the flies arc driven out until only one fly is left to every ten cubic miles, we should have a condition representing the limit that our most sensitive vacuum gauge can measure. Even so, there would still be 20,000 million flies in the sphere. Drive out all but one — that is the scale of a single cæsium atom to a cubic yard — and Langmuir’s method will still detect that lonely fly adrift in the hollow earth.

Such a feat would have delighted Lord Kelvin, to whom science was measurement. It is an example of the exactitude and finesse with which Langmuir is working to-day, pushing yet farther and with surer reach into his chosen world of the infinitely little. There will be other news from him — new frontiers taken, new treasures won. He is fifty-two years old. He varies his intense concentration in the laboratory with many hobbies. He likes music — Beethoven’s symphonies, Wagner’s operas, especially Tristan und Isolde. He flies his own airplane. Week-ends in winter he may be found skate-sailing on Lake George, or skiing in the Adirondacks. He has climbed most of the difficult peaks of the Alps, the Canadian Rockies, the Selkirks. He likes to walk, and once walked fifty-two miles in twenty-four hours. But most of all he likes to experiment with things. And his youthful wish is abundantly fulfilled, for he has a big laboratory at his command, equipped with every known facility, where he is ‘free to do research as I wish.’