Biographies of Scientific Men/Dalton


DALTON

1766-1844

JOHN DALTON, the founder of the chemical atomic theory, was born at Eaglesfield, Cumberland, on 5th September 1766. He was a Quaker, and the son of Joseph and Deborah Dalton; and he attended the village schools until he was eleven years of age. He was a steady-going, thoughtful, and industrious boy.

In 1778 he began to teach in a school at Eaglesfield, but had great trouble to maintain discipline owing to some of his pupils being as old as himself. Disputes were often settled by exhibitions of physical force displayed in the neighbouring churchyard. Three years later he gave up the school, and went as assistant to his cousin, George Bewley, at Kendal, which position he occupied four years. At the end of this time Bewley retired, and the school was continued by the brothers, John and Joseph Dalton, but as teachers they were not popular owing to their uncouth manners.

After leaving Kendal, Dalton went to Manchester as a science tutor to the Manchester New College then
montage of John Dalton and his tomb in Manchester

John Dalton and his tomb in Manchester

existing in the city, and afterwards as a private tutor of science and mathematics. "As a schoolmaster he began life, as a schoolmaster he ended it," but such routine work was not the sole occupation of his mind—far from it.

His scientific Observations upon the Weather were begun on 24th March 1787, and continued until the day before his death (i.e. for over half a century).

In 1794 Dalton was elected a member of the Literary and Philosophical Society of Manchester, and for fifty years he spent his time, in a room of the Society's house in George Street, in teaching, writing, and studying.

His first paper, in 1794, was "Extraordinary Facts relating to the Vision of Colours." Dalton had a defective colour sense, which was amusingly confirmed by the presentation to his mother of a pair of scarlet silk stockings when he was under the impression that they were drab. On another occasion, when selecting cloth for a new suit of clothes, he requested a drab material; a piece caught his eye, and he remarked that it was just what he required, but the tailor informed him it was scarlet cloth for hunting coats.

About this time he published a book on Meteorological Observations and Essays, recording the connection between the aurora borealis and electricity, on the dew-point, thermometers, barometers, etc.

In 1799 he proved that aqueous vapour exists in the atmosphere. In 1800 he published a paper on the conducting power of water for heat; and in 1801 appeared his Constitution of Mixed Gases, wherein he proved "the total pressure of a mixture of two gases on the walls of the containing vessel is equal to the sum of the pressures of each gas; in other words, that if one gas is removed the pressure now exerted by the remaining gas is exactly the same as was exerted by that gas in the original mixture."

It may be mentioned that among Dalton's pupils was the celebrated James Prescott Joule (of the "mechanical equivalent of heat" and the "conservation of energy" fame). Both tutor and pupil are in the first rank of scientific investigators, and hence Manchester has the perhaps unique distinction of having been the home of two of the greatest natural philosophers who ever lived.

John Dalton, the Quaker philosopher, was the founder of the atomic theory, and this great generalization is one of the foundation-stones of modern chemistry.

Leucippus appears to have been the first to grasp the idea that matter is composed of ultimate particles or atoms. Democritus of Abdera (born 460 B.C.) developed the atomic theory of Leucippus, and stated that atoms were impenetrable and indivisible. Epicurus (born 340 B.C.) gave mobility to the atoms, and otherwise greatly improved the atomic theory of the Greek philosophers. According to these sages "the world is composed of an innumerable quantity of atoms, mobile, infinitely small, and distant from each other." These ideas were nothing more than a brilliant speculation. The atomic theory remained a speculation for over two thousand years, until Dalton discovered the law of mutiple proportions, and deduced therefrom that matter is composed of atoms having weights, and that the atoms are of various kinds. When atoms of the same kind come into juxtaposition, elements are formed, such as oxygen, hydrogen, chlorine, etc. Compounds are formed from the juxtaposition of different kinds of atoms, such as water, ammonia, carbon dioxide, etc.

This is not all: to Dalton's law of multiple proportions, the law of Avogadro is adjoined. The latter law establishes that all gases, temperature and pressure being equal, have the same elastic force. As this force is probably due to the shock of atoms or groups of atoms (molecules) on the sides of vessels which contain the gases, it is evident that equal volumes of all elementary gases contain the same number of molecules or atoms. And, finally, Dulong and Petit proved that the atoms of the elements all possess the same specific heat. All these laws, which were the result of observation and experiment in the early part of the nineteenth century, have converted into a scientific theory the ideas of the philosophers of ancient Greece.

Dalton's laboratory was in the lower rooms of the Manchester Literary and Philosophical Society, and "was never remarkable for neatness. … His bottles were of every shape, size, and colour, and his apparatus was of the most humble and inexpensive description. He often performed experiments at the cost of a few shillings on which others would spend as many pounds." What wonderful results were obtained with such meagre appliances! It may be asked whether the laboratories of Lavoisier, Priestley, and Dalton, with their meagre appliances, produced better work than the luxuriously-fitted laboratories of to-day. The question is not easily answered. It must, however, have been simply delightful to have worked under Lavoisier, Priestley, or Dalton, each a genius and pioneer in the early days of modern chemistry. Lavoisier and Dalton were the architects of a new chemistry—a chemistry which has stood the test of time, and is of the greatest value to all nations—in fact, the "wealth of nations."

In 1803 Dalton published a paper "On the Absorption of Gases by Water and other Liquids." This memoir had an important bearing on Henry's law discovered in the same year.

The first account of Dalton's famous atomic theory appeared in Thomson's Chemistry in 1807, he having told Thomson of his experiments and deductions. In 1808 Dalton published his New System of Chemical Philosophy, in which the theory of atoms was fully expounded; and he described experiments directed towards the estimation of the relative weights of atoms. The numbers he obtained as representing the atomic weights were in many cases erroneous; but they were rectified by the work of Berzelius (1779-1848), and even now these constants of nature are subject to frequent revision. It was, however, to the genius of Dalton that the atomic weights of the elements were first comprehended.

Since Dalton's time, the sizes, intervals, and velocities of atoms have been ascertained. These problems have been solved by Clausius, Kelvin, Clerk Maxwell, and others from various sides: "from a comparison with the wave-lengths of light, with the tenuity of the thinnest films of soap-bubbles just before they burst, and from the kinetic theory of gases, involving the dimensions, paths, and velocities of elastic bodies, constantly colliding, and by their impacts producing the resulting pressure on the confining surface." For instance, one cubic centimetre of air contains twenty-one trillions of molecules; the average distance between each molecule equals ninety-five millionths of a millimetre; the average velocity of each molecule is four hundred and forty-seven metres per second; and the average number of impacts received by each molecule is four thousand seven hundred millions per second.

In 1865 Loschmidt of Vienna, twenty-one years after Dalton's death, calculated that the diameter of an atom of oxygen was the one-ten-millionth of a centimetre; and Kelvin came to the conclusion that the distance between the centres of contiguous molecules is less than the one-five-millionth and greater than one-thousand-millionth of a centimetre.

All this work has been the outcome of Dalton's atomic theory. Sir George Darwin says that "within the last few years the electrical researches of Lenard, Röntgen, Becquerel, the Curies, Larmor, Thomson, and a host of others have shown that the atom is not indivisible (as Dalton assumed), and a flood of light has been thrown thereby on the ultimate constitution of matter. Among all these fertile investigators it seems that J. J. Thomson stands pre-eminent, because it is practically through him that we are to-day in a better position for picturing the structure of an atom than was ever the case before. It has been shown that the atom really consists of large numbers of component parts. By various converging lines of experiment it has been proved that the simplest of all atoms, namely, hydrogen consists of about three hundred separate parts; while the number of parts in the atom of the denser metals must be counted by tens of thousands. These separate parts of the atom have been called corpuscles or electrons, and may be described as particles of negative electricity."

As Professor Rutherford says: "It is not true that the discoveries of the last ten years had weakened the atomic theory. On the contrary, they had enormously strengthened it." It is an error to suppose that recent research has removed Dalton's atomic theory or rendered it obsolete. We now know that Dalton's atoms are not atoms, but it is still true that "elements combine in constant proportions by weight." In the words of Sir George Darwin: "The vast edifice of modern chemistry has been built with atomic bricks." From the later work of to-day we know that the atom is not the ultimate form of matter. There are corpuscles and ions inconceivably smaller; but, says Professor A. Smithells, "few will deny that the atomic theory stands to-day an indispensable instrument for productive work; it has neither had its day nor ceased to be. We are now called upon to subdivide our atom, to credit it with an unsuspected store of energy, to consider it a congeries of unsubstantial electrons. There can be no possible objection from our side; it will undo nothing that has been done, and we may have good hopes that it will lead to the doing of many new things in chemistry."

In 1802 Dalton ascertained the composition of the atmosphere, namely, that a hundred volumes contain twenty-one volumes of oxygen and seventy-nine volumes of nitrogen. In 1804 he was asked to give a course of lectures at the Royal Institution of London; and in these lectures he explained his views on the absorption of gases by liquids, on the constitution of gases, etc. As a lecturer, his manner lacked charm and gracefulness, but in spite of these defects his genius was greatly appreciated.

He was a man of great industry, perseverance, and modesty. "It was with difficulty that he accepted any of the numerous honours proffered him. At first declining to become a candidate for the F.R.S., he was elected in 1822 without his knowledge." In 1830 he was elected one of the eight foreign associates of the Académie des Sciences, and in 1832 Oxford University conferred upon him the degree of D.C.L.

In 1822, Dalton visited Paris. Here he met many distinguished men, among whom may be mentioned, Cuvier, Laplace, Gay-Lussac, Arago, Biot, and others.

In 1836 William IV., on the recommendation of Lord Melbourne, granted Dalton a civil list pension of £300 a year.

In 1834 he received the degree of LL.D. from Edinburgh University.

Dalton's private life was monotonous, and to a certain extent uneventful. His character "was most amiable, simple, and unostentatious." His life was in his work. Science was everything to him. The chief recreation in which he indulged was bowls; he belonged to a bowling club which met at the Dog and Partridge Tavern in Manchester. Dalton was of medium height, robust and muscular; his voice was gruff, and his manner curt. When asked why he never married, he replied that he never had time (most likely impecuniosity was the primary cause). He was not, however, totally indifferent to the influence of women, for a warm friendship existed between him and Miss Nancy Wilson. The lady died young, but he always cherished her memory with affection. Another valued friend of Dalton's was Mademoiselle Clementine Cuvier, the daughter of the celebrated naturalist.

Concerning Dalton's atomic theory, it may be stated that he introduced the idea of weights—his theory is essentially one of weight—the relative weights of the different atoms. The first public notice of the atomic theory is contained in his paper, "An Experimental Inquiry into the Proportion of the Several Gases contained in the Atmosphere." He found that oxygen has the power of combining in two different proportions with nitric oxide, forming two distinct bodies, and that the quantities by weight of oxygen which combine are in the simple ratio of one to two. No intermediate compound could be obtained. It was this fact that led to the atomic theory, and the law of multiple proportions. "It is to Dalton—who made his living by giving private lessons at half a crown each—that we owe this knowledge which has made the fortunes of thousands, because he first told us the laws which govern chemical action."

Dalton's atomic theory is, however, somewhat different from the one of to-day. In his day the smallest particle (elementary or compound) was an atom, whereas now compound bodies are composed of atoms of the elements which form the compounds, and are termed molecules. The molecule of a compound contains different atoms, whereas the molecule of an element contains the same atoms.

Although not an accurate manipulator (who could be with such crude apparatus at his disposal?), he was a philosopher, a deep thinker, yea, a genius. He was gifted with that most useful "article"—scientific imagination. "He formed clear mental images of the phenomena which he studied, and these images he was able to combine and modify so that there resulted a new image containing in itself all the essential parts of each separate picture which he had previously formed."

In 1837 his health began to fail and his mental powers to decline; he had a paralytic seizure, but afterwards recovered to a certain extent.

When fainting Nature call'd for aid,
And hovering Death prepared the blow.
Johnson.

Seven years later he had another attack, which proved fatal on 27th July 1844. With public honours his remains were buried in Ardwick Cemetery, Manchester; and a massive tomb of red granite marks the spot where the founder of the atomic theory lies buried.

Of posthumous honours, there is a beautiful statue of Dalton by Sir Francis L. Chantrey in the vestibule of the Manchester Town Hall; and in the same building there is a fresco, by Madox Brown, representing Dalton collecting methane or marsh gas from a stagnant pool. Opposite to Dalton's statue is one of Joule, by Gilbert. These two statues are the most beautiful sculptures Manchester possesses, and they commemorate the life-work of two men who are to the northern city what Shakespeare is to Stratford-on-Avon, or Kelvin to Glasgow. In addition to these honours to Dalton's memory, there are the Dalton chemical and mathematical scholarships awarded by the authorities of the Owens College, Manchester; and a street in Manchester bears his name.

To conclude, the "atomic theory," in the words of the celebrated French chemist Wurtz, "has thrown light upon the most recent discoveries, as it has been, since the time of Dalton, its immortal author, the most perfect instrument in the most profound theoretical conceptions, and the safest guide in experimental researches."