John Dalton

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John Dalton by Charles Turner

John Dalton (6 September 1766 – 27 July 1844) was an English chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory, and his research into colour blindness (sometimes referred to as Daltonism, in his honour).


  • Philosophers are generally persuaded, that the sensations of heat and cold are occasioned by the presence or absence, in degree, of certain principle or quality denominated fire or heat... It is most probable, that all substances whatever contain more or less of this principle. Respecting the nature of the principle, however, there is a diversity of sentiment : some supposing it a substance, others a quality, or property of substance. Boerhaave, followed by most of the moderns, is of the former opinion; Newton, with some others, are of the latter; these conceive heat to consist in an internal vibratory motion of the particles of bodies.
    • Meteorological Observations and Essays: Mit Tabellen, 1834 p. 18
  • 1. Small particles called atoms exist and compose all matter; 2. They are indivisible and indestructible; 3. Atoms of the same chemical element have the same chemical properties and do not transmute or change into different elements.

A New System of Chemical Philosophy (1808)[edit]

Part I

  • When we consider that all elastic fluids are equally expanded by temperature, and that liquids and solids are not so, it should seem that a general law for the affection of elastic fluids for heat, ought to be more easily deducible and more simple than for liquids, or for solids.—There are three suppositions in regard to elastic fluids which merit discussion.
    1. Equal weights of elastic fluids may have the same quantity of heat under like circumstances of temperature and pressure.
    The truth of this supposition is disproved by several facts...
    2. Equal bulks of elastic fluids may have the same quantity of heat with the same pressure and temperature.
    This appears much more plausible... But... considerations... render this supposition extremely improbable, if they do not altogether disprove it. ...
    3. The quantity of heat belonging to the ultimate particles of all elastic fluids, must be the same under the same temperature and pressure.
    It is evident the number of ultimate particles or molecules in a given weight or volume of one gas is not the same as in another... The only answer that can be given... is this.—The particles will condense their respective atmospheres of heat, by which their mutual repulsion will be diminished, and the external pressure will therefore effect a proportionate condensation in the volume of air: neither an increase nor diminution in the quantity of heat around each molecule, or around the whole, will take place. Hence the truth of the supposition, or... proposition, is demonstrated.
    Corol. 1. The specific heats of equal weights of any two elastic fluids, are inversely as the weights of their atoms or molecules.
    Corol. 2. The specific heats of equal bulks of elastic fluids, are directly as their specific gravities, and inversely as the weights of their atoms.
    Corol. 3. Those elastic fluids that have their atoms the most condensed, have the strongest attraction for heat; the greater attraction is spent in accumulating more heat in a given space or volume, but does not increase the quantity around any single atom.
    Corol. 4. When two elastic atoms unite by chemical affinity to form one elastic atom, one half of their heat is disengaged, &c. And in general, when m elastic particles by chemical union become n; the heat given out is to the heat retained as m-n is to n.
  • A pure elastic fluid is one the constituent particles of which are all alike, or in no way distinguishable. Steam, or aqueous vapour, hydrogenous gas, oxygenous gas... and several others are of this kind. ...Whatever ...may be the shape or figure of the solid atom abstractedly, when surrounded by such an atmosphere it must be globular; but as all the globules in any small given volume are subject to the same pressure, they must be equal in bulk, and will therefore be arranged in horizontal strata, like a pile of shot.
    • Ch. II. On the Constitution of Bodies, Sect. 1. On the Constitution of Pure Elastic Fluids
  • When we attempt to conceive the number of particles in an atmosphere, it is somewhat like attempting to conceive the number of stars in the universe; we are confounded with the thought. But if we limit the subject, by taking a given volume of any gas, we seem persuaded that, let the divisions be ever so minute, the number of particles must be finite; just as in a given space of the universe, the number of stars and planets cannot be infinite.
    • Ch. III On Chemical Synthesis
  • Chemical analysis and synthesis go no farther than to the separation of particles one from another, and to 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.
    • Ch. III. On Chemical Synthesis
  • Now it is one great object of this work, to shew the importance and advantage of ascertaining the relative weights of the ultimate particles, both of simple and compound bodies, the number of simple elementary particles which constitute one compound particle, and the number of less compound particles which enter into the formation of one more compound particle.
    • Ch. III. On Chemical Synthesis

Quotes about John Dalton[edit]

  • Dalton's records, carefully preserved for a century, were destroyed during the World War II bombing of Manchester. It is not only the living who are killed in war.
  • From the hour he came from his mother's womb, the God of Nature had laid his hand upon his head, and had ordained him for the ministration of high philosophy. But his natural talents, great as they were, and his almost intuitive skill in tracing the relations of material phaenomena, would have been of comparatively little value to himself and to society, had there not been superadded to them a beautiful moral simplicity and singleness of heart, which made him go on steadily in the way he was before him, without turning to right hand or to the left, and taught him to do homage to no authority before that of truth.
    • Reverend Dr. William Buckland, President of the Geological Society of London. Murray, 1834, found in Meeting of the British Association for the Advancement of Science. p. XI.
  • When one body combines with another in more than one proportion, the second proportion appears to be some multiple or divisor of the first; and this circumstance, observed and ingeniously illustrated by Mr. Dalton, led him to adopt the atomic hypothesis of chemical changes, which had been ably defended by Mr. Higgins in 1789, namely, that the chemical elements consist of certain indestructible particles which unite one and one, or one and two, or in some definite [integer] numbers.
  • The most extraordinary man I met [in Manchester] is John Dalton, whose name is better known in almost any country of Europe than his own, and in any town than in Manchester. He is generally styled by continental writers the Father of Modern Chemistry, and is one of the eight associates of the Institute. Yet this man between sixty and seventy is earning, as I had a peculiar satisfaction in seeing with my own eyes, a penurious existence by teaching boys the elements of mathematics, with which he is so totally occupied, that he can hardly snatch a moment for the prosecution of discoveries which have already put his name on a level with the courtly and courted Davy. But the remarkable thing is that this simple and firm-minded man preserves all the original simplicity and equanimity of his mind, and calmly leaves his fame, like Bacon, to other nations and future ages.'
    • James David Forbes, as quoted by John Campbell Ghairp and Peter Guthrie Tait in Life and letters of James David Forbes p. 450.
  • Another immense service rendered by Dalton, as a corollary of the new atomic doctrine, was the creation of a system of symbolic notation, which not only made the nature of chemical compounds and processes easily intelligible and easy of recollection, but, by its very form, suggested new lines of inquiry. The atomic notation was as serviceable to chemistry as the binomial nomenclature and the classificatory schematism of Linnæus were to zoölogy and botany.
  • In... A New System of Chemical Philosophy published in 1808, John Dalton laid the foundations of the atomic theory: he assumed chemical action to be an action between very minute particles of elements and compounds, and all the minute particles of the same element, or compound, to be exactly the same size and weight. ...his hypothesis assumed the accuracy and universal applicability of those generalisations which are now called the laws of chemical combination.
  • Dalton, the mathematical tutor, following up the lead of Newton, combined the whole of the results of quantitative measurement which had accumulated up to his time, in a comprehensive theory, based on the concept of the chemical atom.
  • He has shewn to us how vividly he formed these ideas, that they were no mere fancies which had passed through his brain, but distinct impressions, ready prepared for utterance. No doubt is left upon our minds as to his opinions, which are, that every piece of matter, even the smallest, must follow the laws of the largest; that when pounds of matter unite, the atoms contained in them must unite also, until we come to the fact that only atoms can really be said to unite. Now as the conception of any fraction of an atom is a contradiction and impossible, they must constantly unite as wholes, and the proportion will be constant. If constant in the smallest quantities, then so in the largest, explaining the permanency of the constitution of bodies so much disputed, and making it a law of nature. If two compound bodies unite, the same law is followed out.

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