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Dalton, John

Category: Scientist

 

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

In 1810, Sir Humphry Davy asked him to offer himself as a candidate for the fellowship of the Royal Society, but Dalton declined; in 1822, however, he was proposed without his knowledge. Six years previously he had been made a corresponding member of the French Académie des Sciences, and in 1830 he was elected as one of its eight foreign associates. He was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1834 at age 68.

He was also elected into the fellowship of the Royal Society of Edinburgh and awarded an honorary degree from the University of Oxford.  In Manchester he was elected president of the Literary and Philosophical Society in 1817, continuing in that office for the rest of his life. The society provided him with a laboratory after the New College moved to York.

Dalton was a devout Quaker and despite his growing affluence and influence, his frugality and modest life style persisted all his life.

Dalton as a scientist

 

As an investigator, Dalton was an avid observer and a very careful recorder.  He recorded more than 200,000 meteorological observations, for example, in his study of the weather. He kept daily weather records from 1787, aged 21,  until his death and his first book was Meteorological Observations (1793).  In the preface to the second part of Volume I of his New System of Chemical Philosophy, he says he had so often been misled by taking for granted the results of others, that he determined to write "as little as possible but what I can attest by my own experience".

He was criticised at the time for using ‘rough and inaccurate instruments, even though better ones were obtainable’, but Dalton was never a rich man and at times he was a very poor man, as such the rough instruments he used were all he could probably afford.  But as Wikipedia says “historians who have replicated some of his crucial experiments have confirmed Dalton's skill and precision”.

Unfortunately, although a keen observer and careful scientist, Dalton was regarded as somewhat of a poor lecturer, and this hampered him in getting his ideas more broadly recognised.  In 1803, he was chosen to give a course of lectures on natural philosophy at the Royal Institution in London, and he delivered another course of lectures there in 1809–1810. Witnesses reported that he was “deficient in the qualities that make an attractive lecturer”. This criticism may sound somewhat unfair, but it has a very serious side.  Dalton’s ideas were not fully understood.  It is clear from his experiments and his notes that the conclusions people have taken away, are not the ones he came to.  If anything people jumped to far too many conclusions.

It is not helped by the fact that the principle books he wrote about his conclusions – several volumes of the New System of Chemical Philosophy at around 450 pages each – are not exactly bedtime reading. 

Remembering the effort that Dalton had also expended on his meteorological diary, the more than 200,000 observations all explained in his Meteorological Observations and Essays , his lack of communication skills was evident.  In spite of the originality of his treatment, little attention was paid to the book by other scholars.

He was a very good scientist, the evidence is there in plenty, but he was not a very good communicator. 

Atomic theory

 

Dalton arrived at his view of atomism by two routes – those of his observations in meteorology, in which [as we have seen] he had a lifelong interest and in the work of the early philosophers, principally the Greek philosophers.  The concept of the atom was not new, Dalton did not ‘discover’ the atom, but his achievement was in scientifically proving that the hypothesis that atoms exist was true, and in giving them a weighting factor, and he did it principally via experiments with gases. 

Thus this is not to downplay the role Dalton played in atomic theory, but it would be wrong to attribute atomic theory to him.  An atomic theory already existed, what Dalton set out to do and also add to, is to prove the theory and add to it via atomic ‘weightings’.

Some history

Atoms were a concept used in Greek philosophy several thousand years ago. The very word atom comes from the Ancient Greek adjective atomos, meaning "indivisible”:

Fr 117 Diogenes Laertius IX 72
Democritus says:  By convention hot, by convention cold, but in reality atoms and void, and also in reality we know nothing, since the truth is at bottom

 

In India, Maharshi Kanada (Sanskrit: कणाद) was a sage and philosopher who founded the philosophical school of Vaisheshika and authored the text Vaisheshika Sutra.  Kanada was a scientist and mystic.  There is some debate about when he lived, with dates ranging from the 6th century BCE to the 2nd century BCE. 

Kanada too is credited with the idea of ‘the atom’.  Kanada’s atom was ‘spiritual’, - that is ‘ordered energy’ just as it was for all the Greek philosophers.  Kanada conceived of the atom as an Egg shaped spiritual object that mirrored the universe itself.  The atom was composed of five levels and layers Water, Fire, Earth, Air, and Aether.  There was no division of the Aether level into its constituent sub- levels, but he greatly expanded on how the atom – or as he called it the anu worked.

Kanada also conceived of the two states used in the atom – which he defined as Absolute rest or a State of motion. In effect, he also defined the unit of energy.  Adherents of the school of philosophy founded by Kanada, considered the atom to be indestructible, and hence eternal. Thus the universe is a collection of indestructible atoms made of energy

Kanada also conceived of the idea of aggregates – called in his system dvyanuka and tryanuka

He decided that the functions of the universe were governed by these atoms and that all the changes and motion we see in objects is due to the functions they have activating.  He gave the blackening of an earthen pot and the ripening of fruit as examples of this phenomenon.  In the words of A.L. Basham, the ‘veteran Australian Indologist’ “they were brilliant imaginative explanations of the structure of the world.”

All these theories are expounded in the Vaisesika Sutras, which are a blend of science, philosophy and mysticism. 

Dalton and the Laws of Attraction and Repulsion

 

The concept of weight and mass is actually a meaningless term.  There were two laws recognised in the time of Newton and Dalton, those of attraction and repulsion.  Newton’s laws of gravity are simply a specific case of the overall laws of attraction.

One of the deductions Dalton had been able to make via his Meteorological Observations, was that ‘air’ is, in some senses, a physically apparent system; the pressure exerted by each gas in a mixture is independent of the pressure exerted by the other gases; the total pressure is the sum of the pressures of each gas. In explaining the law of partial pressures, Dalton stated very clearly that the forces of repulsion thought to cause pressure acted between atoms of the same kind and that the atoms in a mixture were indeed different in weight and “complexity.”

At no time did Dalton thus say, the atoms were physical different things – they had different functions, and appeared to attract or repulse things differently.

In other words, the different forces of repulsion produced by the different types of atoms result in different pressures in the mixture. We can think of this as though the atoms had invisible boundaries which gave the impression that they were of different sizes, but in actuality simply defined their different forces of repulsion.   

Rayleigh scattering and Brownian motion

Hypothetically, Rayleigh scattering is simply an example of this overall feature.  Rayleigh scattering, named after the British physicist Lord Rayleigh, is the scattering of light or other electromagnetic ‘radiation’ by particles much smaller than the wavelength of the radiation. But radiation can also be thought of as a bubble of energy with defined functions, it is just that we cannot see it.

three dimensional Brownian motion

It may also account for Brownian motion - Brownian motion is the random motion of particles [this time bigger particles] suspended in a fluid (a liquid or a gas).  The explanation given is that this is due to “their collision with the fast-moving atoms or molecules in the gas or liquid”, without any indication of why they should be fast moving.  But a theory that relies on forces of repulsion and attraction is a far better explanation.  Think of it analogously as a man attempting to walk through a crowd, where each person each has differing needs for ‘personal space’, he would be shoved forward, back, from side to side apparently at random, but actually  according to laws.

Gas laws and spinning

As we have seen by the quote, below, it was known thousands of years ago that heating a solid produces first a liquid and then a gas and of course vice versa, cooling a gas produces a liquid and then a solid

Fr 117 Diogenes Laertius IX 72
Democritus says:  By convention hot, by convention cold, but in reality atoms and void

Why did Democritus say ‘by convention’?  Because heat and cold are simply changes to the unit of energy spin rate, raising and lowering the overall levels at which the atom ‘vibrates’ [figuratively speaking].  Dalton was not aware of this, nor did he ever rediscover it, but in his four essays, presented between 2 and 30 October 1801 and published in the Memoirs of the Literary and Philosophical Society of Manchester in 1802, the second of these essays opens with this statement:

There can scarcely be a doubt entertained respecting the reducibility of all elastic fluids of whatever kind, into liquids; and we ought not to despair of effecting [sic] it in low temperatures and by strong pressures exerted upon the unmixed gases further.

In the fourth essay he remarks,

I see no sufficient reason why we may not conclude that all elastic fluids under the same pressure expand equally by heat and that for any given expansion of mercury, the corresponding expansion of air is proportionally something less, the higher the temperature. It seems, therefore, that general laws respecting the absolute quantity and the nature of heat are more likely to be derived from elastic fluids than from other substances.

The law of multiple proportions

The law of definite proportions was first proved by the French chemist Joseph Louis Proust in 1799, this law states that if a compound is broken down into its constituent elements, then the masses of the constituents will always have the same proportions, regardless of the quantity or source of the original substance.

John Dalton studied and expanded upon this previous work and developed the law of multiple proportions: if two elements can be combined to form a number of possible compounds, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers. For example: Proust had studied tin oxides and found that their masses were either 88.1% tin and 11.9% oxygen or 78.7% tin and 21.3% oxygen (these were tin(II) oxide and tin dioxide respectively). Dalton noted from these percentages that 100g of tin will combine either with 13.5g or 27g of oxygen; 13.5 and 27 form a ratio of 1:2. Dalton found that an atomic theory of matter could elegantly explain this common pattern in chemistry. In the case of Proust's tin oxides, one tin atom will combine with either one or two oxygen atoms.

Aggregates and weighting factors

 

Atoms form themselves into aggregates and thereby become a new named entity via the forces/function of attraction.  Attraction is thus both a creative force binding new atoms together, but, depending of the ‘tightness’ of the binding – a strong attraction or a weak attraction – then the density will differ and the mass’ or weight will differ.

Thus a ‘heavy’ compound  or element is simply one whose forces of attraction are higher.  If we take lead as an example, the atoms must have strong attractive forces/functions, and the atoms themselves will thus cluster closer together, making them appear more ‘solid’ to us, and furthermore, their strong attractive force will make them appear ‘heavier’.

Repulsion is an opposite force or function to attraction.  Thus it will appear to make things ‘lighter’,  the ‘weight’ or ‘mass’ of any object is thus the balance of the two forces for any one atom or corresponding group of atoms.   A predominance of repulsion over attraction will produce lighter substances such as gases, whereas a predominance of attractive forces over repulsive forces will produce heavy objects such as the metals.

Atomists from the Greek philosopher Democritus to the 18th-century mathematician and astronomer Ruggero Giuseppe Boscovich, had already stated that atoms of all kinds of matter are the same in principal. Dalton simply added that atoms of different elements vary in mass, and indeed this claim is the cardinal feature of his atomic theory. But here we must take this to mean the balance of attractive and repulsive forces. 

Thus what Dalton recognised was that:

  • Atoms – even though they may be the same thing in the sense of a basic indivisible unit of ordered energy – they may be functionally  [and this is key] – and behaviourally different.  Thus an atom is always an atom, but sometimes it has carbon functions ‘turned on’ and behaves like carbon, and sometimes it has oxygen functions ‘turned on’ and behaves like oxygen
  • Mass – One of the perceived functions and behaviours of all atoms was their ‘weight’, their mass, and this also determined what they were as well.  As such the atomic weights – the balance between repulsive and attractive forces are a reflection of the functions they exhibit.

The mistake that has been made since Dalton first proposed this is to assume that atoms are somehow ‘physically different’, as though they were different shaped balls in a box.  This is not what Dalton proposed, he simply said ‘they are different’.  Dalton focused upon determining the relative masses of each different kind of atom, a process that could be accomplished, he claimed, only by considering the number of atoms of each element present in different chemical compounds.

Experimental support

 

A study of Dalton's own laboratory notebooks, discovered in the rooms of the Lit & Phil, concluded that the idea of atoms of this sort arose in his mind as a purely conceptual one, but he was helped by his study of the properties of the atmosphere and other gases. The first published indications of this idea are to be found at the end of his paper on the absorption of gases, which was read on 21 October 1803, though not published until 1805. Here he says:

Why does not water admit its bulk of every kind of gas alike? This question I have duly considered, and though I am not able to satisfy myself completely I am nearly persuaded that the circumstance depends on the weight and number of the ultimate particles of the several gases.

Dalton found that water absorbed carbon dioxide, for example, far better than it absorbed nitrogen and hypothesized this was due to the differences in mass and complexity of the gases' respective particles. Indeed, carbon dioxide molecules (CO2) are ‘heavier’ and exert a larger attractive force than nitrogen molecules (N2).

Dalton proposed that each chemical element is composed of atoms of a single, unique type, and though they cannot be altered or destroyed by chemical means, they can combine to form more complex structures (chemical compounds). This marked the first truly scientific theory of the atom, since Dalton reached his conclusions by experimentation and examination of the results in an empirical fashion.

In a memoir read to the Manchester Literary and Philosophical Society on October 21, 1803, he further stated that:

“An inquiry into the relative weights of the ultimate particles of bodies is a subject, as far as I know, entirely new; I have lately been prosecuting this inquiry with remarkable success.”

But ‘weighing’ can only ever be achieved by having a fixed unit of measure with which one can estimate proportional or comparative ‘weights’.  The ‘weight’ is not an absolute number, one fixes a starting point for an element at 1 and then expresses the other ‘weights’ – measurements - by comparison with this basic first unit.  Dalton measured the masses of these elements, including hydrogen, oxygen, carbon, and nitrogen, by recording and measuring in which proportions they combined with each other.   

Encyclopædia Britannica, Inc. - Atomic theory - Sydney Ross

Dalton’s measurements allowed him to formulate the Law of Multiple Proportions: When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers. Thus, taking the elements as A and B, various combinations between them naturally occur according to the mass ratios A:B = x:y or x:2y or 2x:y, and so on. Different compounds were formed by combining atomic building blocks of different masses.  The problem remained, however, that a knowledge of ratios was insufficient to determine the actual number of elemental atoms in each compound.

For example, Dalton found that methane contained twice as much hydrogen as ethylene. But without knowing the attraction/repulsion ratio one cannot actually calculate the number of each type of atom.

 

Dalton invented a rule of “greatest simplicity,” as a starting point - namely, that AB is the most likely combination.  This was merely an assumption, derived from faith in the simplicity of nature. No evidence was then available to be able to deduce how many atoms of each element combine to form compound molecules.

But this or some other such rule was absolutely necessary to any incipient theory.  He assigned methane a combination of one carbon and two hydrogen atoms, for example, and ethylene a combination of one carbon and one hydrogen atom.   We now know that the rule of greatest simplicity is incorrect, for the methane molecule is chemically symbolized as CH4 and the ethylene molecule as C2H4. Nevertheless, Dalton’s atomic theory triumphed over its weaknesses because his foundational argument was correct.

In 1858, the Italian chemist Stanislao Cannizzaro pointed out the utility of Amadeo Avogadro’s hypothesis in determining ‘molecular masses’ – weighting factors for molecules as a whole. Since then, chemists have shown the theory of Daltonian atomism to be a key factor underlying further advances in their field. Organic chemistry in particular progressed rapidly once Dalton’s theory gained acceptance.

The main points of Dalton's atomic theory are thus:

  • Elements are made of atoms, which are themselves the basic building block of all aggregates.
  • Atoms of a given element are identical in mass, apparent size [taking into account their repulsion/attraction ratio], and other properties/functions; atoms of different elements differ in apparent size, mass, and other properties/functions.
  • Atoms cannot be subdivided, created, or destroyed.
  • Atoms of different elements combine in simple whole-number ratios to form chemical compounds, which exhibit new and different properties/functions, mass, and again an apparent size [taking into account their repulsion/attraction ratio].
  • In chemical reactions, atoms are combined, separated, or rearranged.

 

Despite being called an atomic theory, Dalton’s proposal was actually a chemist’s theory, the apparent processes of nuclear fusion and nuclear fission, are classified as nuclear reactions and deserve a special explanation of their own.

 

Colour blindness

Dalton was one of the first to systematically describe colour blindness and the main reason he noticed it and could describe it, is that he was himself colour blind. Since his brother was also colour blind, he also correctly concluded that it was inherited. Dalton could see blue, but "orange, yellow and green seem one colour which descends pretty uniformly from an intense to a rare yellow, making what I should call different shades of yellow….. that part of the image which others call red appears to me little more than a shade or defect of light.”

Dalton's thorough and methodical research into his own visual problem was so broadly recognized that Daltonism became a common term for colour blindness. Examination of his preserved eyeball in 1995 demonstrated that Dalton actually had a less common kind of colour blindness, deuteroanopia, in which medium wavelength sensitive cones are missing, the most common type of colour blindness is called deuteroanomaly.

In 1794 at age 28, Dalton was elected a member of the Manchester Literary and Philosophical Society, the "Lit & Phil", and a few weeks later he communicated his first paper on "Extraordinary facts relating to the vision of colours".  His theory as to why it happened proved wrong, but his observation that it did happen opened the door for research into the area.

Life

 

John Dalton was born into a Quaker family in Eaglesfield, near Cockermouth, in the county of Cumberland, England 6th September 1766. His father was a weaver. He received his early education from his father and from Quaker John Fletcher, who ran a private school in the nearby village of Pardshaw Hall.

With his family too poor to support him for long, he began to earn his living at the age of ten in the service of a wealthy and prominent Eaglesfield Quaker named, Elihu Robinson. Dalton's early life was highly influenced by Elihu Robinson, who was a competent meteorologist and instrument maker.  Robinson got him interested in problems of mathematics and meteorology.

For most of his life—beginning in his village school at the age of 12— he earned his living as a teacher; he was proficient in Latin at age 14.  He joined his older brother Jonathan at age 15 in running a Quaker school in Kendal, about forty five miles from his home. Being a Dissenter, he was barred from attending English universities. He acquired much scientific knowledge from informal instruction by John Gough, a blind philosopher who was gifted in the sciences and arts. He taught for 10 years at the Quaker boarding school in Kendal, and during his years in Kendal, contributed solutions of problems and questions on various subjects to The Ladies' Diary and the Gentleman's Diary.

At age 27 in 1793, he was appointed Professor of Mathematics and Natural Philosophy at the "New College" in Manchester, a dissenting academy. There he joined the Manchester Literary and Philosophical Society, which provided him with a stimulating intellectual environment and laboratory facilities. As we have seen, the first paper he delivered before the society was on colour blindness.

He remained there until age 34, when the college's worsening financial situation led him to resign his post and begin a new career as a private tutor for mathematics and natural philosophy.  In 1800, at age 34 Dalton became the secretary of the Manchester Literary and Philosophical Society.

Dalton never married and had only a few close friends. All in all, as a Quaker he lived a modest and unassuming personal life.

For the twenty-six years prior to Dalton's death, he lived in a room in the home of the Rev. (and Mrs.) W. Johns, a published botanist, in George Street, Manchester. Dalton and Johns died in the same year – 1844.  In 1833, at age 67 Earl Grey's government conferred on him a pension of £150, raised in 1836 to £300.

Dalton's daily round of laboratory work and tutoring in Manchester was broken only by annual excursions to the Lake District and occasional visits to London. In 1822 he paid a short visit to Paris, where he met many distinguished resident men of science. He attended several of the earlier meetings of the British Association at York, Oxford, Dublin and Bristol.

Death

 

Dalton suffered a minor stroke in 1837, and a second one in 1838 left him with a speech impairment, though he remained able to perform experiments. In May 1844 he had yet another stroke; on 26 July 1844 he recorded with trembling hand his last meteorological observation. On 27 July 1844, in Manchester, Dalton fell from his bed and was found lifeless by his attendant.

Dalton was accorded a civic funeral with full honours. His body was laid in state in Manchester Town Hall for four days and more than 40,000 people filed past his coffin. The funeral procession included representatives of the city’s major civic, commercial, and scientific bodies.

Quakers in Science and Industry
His life always remained that of a simple, kindly, shy man, a true Friend, unostentatious, devoted to his work and not seeking either honours or rewards.  He maintained the plain speech and dress of the Quakers and attended meeting for worship regularly to the end of his life.  His will indicated his interests, dying unmarried he left £50 to the Eaglesfield and Bethel school; £300 to Friends school, Wigton and £500 to Ackworth school… He will remain forever one of the great pioneers of science and a truly simple and humble friend.

 

References

  • Dalton, John - Memoir on sulphuric ether, 1820 (short work)
  • Dalton, John  - The book of philosophical experiments, 1839
  • Dalton, John (1834). Meteorological Observations and Essays (2 ed.). Manchester: Harrison and Crosfield.
  • Dalton, John (1893). Foundations of the Atomic Theory. Edinburgh: William F. Clay.– Alembic Club reprint with some of Dalton's papers, along with some by William Hyde Wollaston and Thomas Thomson
  • Dalton, John (1808). A new system of chemical philosophy.  Now Volumes 1 and 2; originally published as PartI 1808; Part II 1810 and Part III 1827
  • John Dalton Papers at John Rylands Library, Manchester.
  • Dalton, John - Elements of English Grammar - Dalton made a study on the grammatical subjects of the auxiliary verbs and participles of the English language.  This book was published at age 35 in 1801.
  • Rees's Cyclopædia  - Dalton contributed articles on Chemistry and Meteorology.
  • Memoirs of the Literary and Philosophical Society  - Dalton contributed 117 Memoirs from 1817 until his death in 1840, while president of that organization. In one of them, in 1814, he explains the principles of volumetric analysis, in which he was one of the earliest workers. In 1840 a paper on the phosphates and arsenates was refused by the Royal Society, but published by himself. He took the same course soon afterwards with four other papers, two of which (On the quantity of acids, bases and salts in different varieties of salts and On a new and easy method of analysing sugar) contain his discovery, regarded by him as second in importance only to the atomic theory, that certain anhydrates, when dissolved in water, cause no increase in its volume.

Observations

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