John Dalton

John Dalton (September 6, 1766 – July 27, 1844) was a British chemist and physicist, born at Eaglesfield, near Cockermouth in Cumberland. He is most well known for his advocacy of the atomic theory.

Biography

Early life

John Dalton was born September 6, 1766 in Eaglesfield, Cumberland and received his early education from his father and from John Fletcher, a teacher of the Quaker school at Cumberland, on whose retirement in 1778 he himself started teaching. This youthful venture was not successful, the amount he received in fees being only about five shillings a week, and after two years he took to farm work. But he had received some instruction in mathematics from a distant relative, Elihu Robinson, and in 1781 he left his native village to become helper to his cousin George Bewley, who kept a school at Kendal. There he passed the next twelve years, becoming in 1785, through the retirement of his cousin, joint manager of the school with his elder brother Jonathan. Dalton was unable to attend both Oxford and Cambridge university because they were only open to members of the Church of England.

About 1790 he seems to have thought of taking up law or medicine, but his projects met with no encouragement from his relatives and he remained at Kendal until, in the spring of 1793, he moved to Manchester. Mainly through John Gough, a blind philosopher to whose aid he owed much of his scientific knowledge, he was appointed teacher of mathematics and natural philosophy at the Manchester Academy. He remained in that position until the relocation of the college to York in 1803, when he became a public and private teacher of mathematics and chemistry. Among his pupils were: Eaton Hodgkinson and James Prescott Joule.

Meteorology, vision and miscellany

In the early portion of Dalton's teaching career Dalton's way of life was influenced by a prosperous Quaker, a competent meteorologist and instrument maker, who got him interested in the problems of mathematics and meteorology. During his years in Kendal, Dalton had contributed solutions of problems and questions on various subjects to the Gentlemen's and Ladies' Diaries, and in 1787 he began to keep a meteorological diary in which, during the succeeding fifteen years, he entered more than 200,000 observations. His first separate publication was Meteorological Observations and Essays (1793), which contained the germs of several of his later discoveries. However, in spite of the originality of his treatment, the book met with only a limited sale.

Another work by him, Elements of English Grammar, was published in 1801. In 1794 he was elected a member of the Manchester Literary and Philosophical Society, the Lit & Phil, and a few weeks after election he communicated his first paper on Extraordinary facts relating to the vision of colours, in which he postulated that shortage in color perception was caused by discoloration of the liquid medium of the eyeball. Although Dalton's theory lost credence in his own lifetime, the thorough, methodical nature of his research was so broadly recognized that Daltonism became a common term for color blindness. Besides the blue and purple of the spectrum he was able to recognize only one colour, yellow, or, as he says in his paper, "that part of the image which others call red appears to me little more than a shade or defect of light. After that the 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".

This paper was followed by many others on diverse topics on rain and dew and the origin of springs, on heat, the colour of the sky, steam, the auxiliary verbs and participles of the English language and the reflection and refraction of light.

Atomic theory

In 1800 he became a secretary of the Manchester Literary and Philosophical Society, and in the following year he presented the important paper or series of papers, entitled Experimental Essays on the constitution of mixed gases; on the pressure of steam and other vapors at different temperatures, both in a vacuum and in air; on evaporation; and on the thermal expansion of gases.

The second of these essays opens with the striking remark,

"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 affecting it in low temperatures and by strong pressures exerted upon the unmixed gases further."

After describing experiments to ascertain the pressure of steam at various points between 0 ° and 100°C (32° and 212°F), he concluded from observations on the vapor pressure of six different liquids, that the variation of vapor pressure for all liquids is equivalent, for the same variation of temperature, reckoning from vapor of any given pressure.

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."

He thus enunciated Gay-Lussac's law, stated some months later by Joseph Louis Gay-Lussac. In the two or three years following the reading of these essays, he published several papers on similar topics, that on the absorption of gases by water and other liquids (1803), containing his law of partial pressures.

The most important of all Dalton's investigations are those concerned with the atomic theory in chemistry, with which his name is inseparably associated. It has been proposed that this theory was suggested to him either by researches on ethylene (olefiant gas) and methane (carburetted hydrogen) or by analysis of nitrous oxide (protoxide of azote) and nitrogen dioxide (deutoxide of azote), both views resting on the authority of Thomas Thomson. However, a study of Dalton's own laboratory notebooks, discovered in the rooms of the Lit & PhilRoscoe & Harden (1896), concluded that so far from Dalton being led to the idea, that chemical combination consists in the interaction of atoms of definite and characteristic weight, by his search for an explanation of the law of multiple proportions, the idea of atomic structure arose in his mind as a purely physical concept, forced upon him by study of the physical 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 already mentioned, which was read on October 21 1803 though not published till 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."

He proceeds to give what has been quoted as his first table of atomic weights, but in his laboratory notebooksLaboratory notebooks for 1802–1804, under the date 6th September 1803, on p.248 there is an earlier one dated 1803 in which he sets out the relative weights of the atoms of a number of substances, derived from analysis of water, ammonia, carbon dioxide, etc. by chemists of the time.

It appears, then, that confronted with the problem of calculating the relative diameter of the atoms of which, he was convinced, all gases were made, he used the results of chemical analysis. Assisted by the assumption that combination always takes place in the simplest possible way, he thus arrived at the idea that chemical combination takes place between particles of different weights, and this it was which differentiated his theory from the historic speculations of the Greeks.

The extension of this idea to substances in general necessarily led him to the law of multiple proportions, and the comparison with experiment brilliantly confirmed his deductionRoscoe & Harden (1896), pp. 50,51. It may be noted that in a paper on the proportion of the gases or elastic fluids constituting the atmosphere, read by him in November 1802, the law of multiple proportions appears to be anticipated in the words: "The elements of oxygen may combine with a certain portion of nitrous gas or with twice that portion, but with no intermediate quantity", but there is reason to suspect that this sentence was added some time after the reading of the paper, which was not published till 1805.

Compounds were listed as binary, ternary, etc. in the New System of Chemical Philosophy depending on the number of atoms a compound had in its simplest, empirical form.

He hypothesized the structure of compounds can be represented in whole number ratios. So, one atom of element X combining with one atom of element Y is a binary compound. Furthermore, one atom of element X combining with two elements of Y or vice versa, is a ternary compound. Many of the first compounds listed in the New System of Chemical Philosophy were listed correctly, although others have not.

Dalton used his own symbols to visually represent the atomic structure of compounds. These have made it in New System of Chemical Philosophy where John Dalton listed a number of elements, and common compounds.

Many of Dalton's ideas were acquired from other chemists at the time, such as Antoine Lavoisier and William Higgins. However, he was the first to put the ideas into a universal atomic theory, which was undoubtedly his greatest achievement.

Five main points of Dalton's Atomic Theory

Elements are made of tiny particles called atoms
All atoms of a given element are identical
The atoms of a given element are different from those of any other element
Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers of types of atoms.
Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process. A chemical reaction simply changes the way atoms are grouped together.

Unfortunately, Dalton had an additional statement that prevented his theory from being accepted for many years.

When atoms combine in only one ratio, "..it must be presumed to be a binary one, unless some cause appear to the contrary"

Dalton had no evidence to support this statement from his theory and it caused him to wrongly assume that the formula for water was OH and ammonia was NH. Because of this Daltons experimental data did not support most of the conclusions he drew from it.

Amazingly, all but two of the statements in Dalton's Atomic Theory are still believed to be true by scientists today. The statement "Atoms cannot be created, divided into smaller particles, or destroyed" is inconsistent with the existence of nuclear fusion and fission, although such processes are nuclear reactions, not chemical reactions. In addition, the statement "all atoms of a given element are identical" is not precisely true, as the different isotopes of an element have varying numbers of neutrons in their nuclei, though the number of protons remains consistent.

Later years

Dalton communicated his atomic theory to Thomson who, by consent, included an outline of it in the third edition of his System of Chemistry (1807), and Dalton gave a further account of it in the first part of the first volume of his New System of Chemical Philosophy (1808). The second part of this volume appeared in 1810, but the first part of the second volume was not issued till 1827, though the printing of it began in 1817. This delay is not explained by any excess of care in preparation, for much of the matter was out of date and the appendix giving the author's latest views is the only portion of special interest. The second part of vol. ii. never appeared.

Dalton was president of the Lit & Phil from 1817 until his death, contributing 116 memoirs. Of these the earlier are the most important. In one of them, read 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, often regarded as a weaker work, was refused by the Royal Society, and he was so incensed that he published it 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, his inference being that the salt enters into the pores of the water.

Dalton's experimental method

As an investigator, Dalton was content with rough and inaccurate instruments, though better ones were readily attainable. Sir Humphry Davy described him as "a very coarse experimenter", who almost always found the results he required, trusting to his head rather than his hands.

In the preface to the second part of vol. i. of his New System 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", but this independence he carried so far that it sometimes resembled lack of receptivity. Thus he distrusted, and probably never fully accepted, Gay-Lussac's conclusions as to the combining volumes of gases. He held peculiar and quite unfounded views about chlorine. Even after its elementary character had been settled by Davy, he persisted in using the atomic weights he himself had adopted, even when they had been superseded by the more accurate determinations of other chemists. He always objected to the chemical notation devised by Jöns Jakob Berzelius, although by common consent it was much simpler and more convenient than his own cumbersome system of circular symbols. His library, he was once heard to declare, he could carry on his back, yet reputedly he had not read half the books it contained.

Public life

Before he had propounded the atomic theory, he had already attained a considerable scientific reputation. In 1804 he was chosen to give a course of lectures on natural philosophy at the Royal Institution in London, where he delivered another course in 1809–1810. However, he was deficient, it would seem, in the qualities that make an attractive lecturer, being harsh and indistinct in voice, ineffective in the treatment of his subject, and singularly wanting in the language and power of illustration.

In 1810 he was asked by Davy to offer himself as a candidate for the fellowship of the Royal Society, but declined, possibly for financial reasons. However, in 1822 he was proposed without his knowledge, and on election paid the usual fee. 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 in place of Davy.

In 1833 Lord Grey's government conferred on him a pension of £150, raised in 1836 to £300.

Dalton never married And didn’t really have many friends throughout his life. He lived for more than a quarter of a century with his friend the Rev. W. Johns (1771–1845), in George Street, Manchester, where his daily round of laboratory work and tuition 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 scientists. He attended several of the earlier meetings of the British Association at York, Oxford, Dublin and Bristol.

Death and legacy

Dalton died in Manchester in 1844 of paralysis. The first attack he suffered in 1837, and a second in 1838 left him with a speech impediment, though he remained able to make experiments. In May 1844 he had another stroke; on July 26 he recorded with trembling hand his last meteorological observation, and on the 27th he fell from his bed and was found lifeless by his attendant. A bust of him, by Chantrey, was publicly subscribed for him and placed in the entrance hall of the Manchester Royal Institution.

Dalton had requested that his eyes be examined after his death, in an attempt to discover the cause of his colour-blindness; he had hypothesised that his aqueous humour might be coloured blue. Postmortem examination showed that the humours of the eye were perfectly normal. However, an eye was preserved at the Royal Institution, and a 1990s study on DNA extracted from the eye showed that he had lacked the pigment that gives sensitivity to green; the classic condition known as a deuteranope.

In honor of his work with ratios and chemicals that led to the idea of atoms and atomic weights, many chemists and biochemists use the (as of yet unofficial) unit Dalton (abbreviated Da) to denote one atomic mass unit, or 1/12 the weight of a neutral atom of Carbon-12.

In his book The 100, Michael H. Hart ranks Dalton as the 32nd most influential person in history.

References

Bibliography

Henry, Life of Dalton, Cavendish Society (1854)
Angus Smith, Memoir of John Dalton and History of the Atomic Theory
Roscoe and Harden, A New View of the Origin of Dalton's Atomic Theory (1896)
Arnold Thackray, John Dalton: Critical Assessments of His Life and Science, Harvard University Press, (1972) ISBN 0674475259
DM Hunt, KS Dulai, JK Bowmaker, JD Mollon, "The Chemistry of John Dalton's Color Blindness", Science, February 17 1995

External links

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