John Dalton


John Dalton was an English chemist, physicist, and meteorologist whose work laid the foundations of modern atomic theory and stoichiometric chemistry. Building on earlier ideas about the indivisibility of matter and his own precise measurements of combining ratios, Dalton proposed that each chemical element consists of identical atoms of characteristic weight, and that compounds are formed when atoms of different elements combine in fixed whole-number proportions. His A New System of Chemical Philosophy presented a coherent atomic model, supplied relative atomic weights and symbolic notation, and established the quantitative framework that shaped nineteenth-century chemistry and remains the basis of modern chemical thought.
Dalton was also a pioneering meteorologist and physicist, keeping daily weather observations for over fifty years, formulating the first empirical law of partial pressures, and studying the behavior of gases through his work on vapor pressure and gas solubility. His investigations into his own color blindness led to the first scientific description of the condition—still called Daltonism in several languages—and helped establish experimental methods for linking perception with physiology. Elected a Fellow of the Royal Society in 1822 and awarded its Royal Medal in 1826, Dalton became the first British scientist to develop a quantitative atomic theory and one of the key figures in the transition of chemistry from a qualitative to a mathematical science.
In honour of Dalton's work, a unit of atomic mass, the dalton, symbol Da, is officially accepted for use with the SI.

Early life

John Dalton was born on 5 or 6 September 1766 into a Quaker family in Eaglesfield, near Cockermouth, in Cumberland, England. 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. Dalton's family was too poor to support him for long and he began to earn his living, from the age of ten, in the service of wealthy local Quaker Elihu Robinson.

Scientific work

Meteorology

Dalton's early life was influenced by a prominent Quaker, Elihu Robinson, a competent meteorologist and instrument maker, from Eaglesfield, Cumberland, who interested him in problems of mathematics and meteorology. During his years in Kendal, Dalton contributed solutions to problems and answered questions on various subjects in The Ladies' Diary and the Gentleman's Diary. In 1787 at age 21 he began his meteorological diary in which, during the succeeding 57 years, he entered more than 200,000 observations. He rediscovered George Hadley's theory of atmospheric circulation around this time. In 1793 Dalton's first publication, Meteorological Observations and Essays, contained the seeds of several of his later discoveries but despite the originality of his treatment, little attention was paid to them by other scholars. A second work by Dalton, Elements of English Grammar, was published in 1801.

Measuring mountains

After leaving the Lake District, Dalton returned annually to spend his holidays studying meteorology, something which involved a lot of hill-walking. Until the advent of aeroplanes and weather balloons, the only way to make measurements of temperature and humidity at altitude was to climb a mountain. Dalton estimated the height using a barometer. The Ordnance Survey did not publish maps for the Lake District until the 1860s. Before then, Dalton was one of the few authorities on the heights of the region's mountains. He was often accompanied by Jonathan Otley, who also made a study of the heights of the local peaks, using Dalton's figures as a comparison to check his work. Otley published his information in his map of 1818. Otley became both an assistant and a friend to Dalton.

Colour blindness

In 1794, shortly after his arrival in Manchester, 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", in which he postulated that shortage in colour perception was caused by discoloration of the liquid medium of the eyeball. As both he and his brother were colour blind, he recognised that the condition must be hereditary.
Although Dalton's theory was later disproven, his early research into colour vision deficiency was recognized after his lifetime. Examination of his preserved eyeball in 1995 demonstrated that Dalton had deuteranopia, a type of congenital red-green color blindness in which the gene for medium wavelength sensitive photopsins is missing. Individuals with this form of colour blindness see every colour as mapped to blue, yellow or gray, or, as Dalton wrote in his seminal paper,

Gas laws

In 1800, Dalton became secretary of the Manchester Literary and Philosophical Society, and in the following year he presented an important series of lectures, entitled "Experimental Essays" on the constitution of mixed gases; the pressure of steam and other vapours at different temperatures in a vacuum and in air; on evaporation; and on the thermal expansion of gases. The four essays, presented between 2 and 30 October 1801, were published in the Memoirs of the Literary and Philosophical Society of Manchester in 1802.
The second essay opens with the remark,
After describing experiments to ascertain the pressure of steam at various points between, Dalton concluded from observations of the vapour pressure of six different liquids, that the variation of vapour pressure for all liquids is equivalent, for the same variation of temperature, reckoning from vapour of any given pressure.
In the fourth essay he remarks,
He enunciated Gay-Lussac's law, published in 1802 by Joseph Louis Gay-Lussac. In the two or three years following the lectures, Dalton published several papers on similar topics. "On the Absorption of Gases by Water and other Liquids" contained his law of partial pressures now known as Dalton's law.

Atomic theory

Arguably the most important of all Dalton's investigations are concerned with the atomic theory in chemistry. While his name is inseparably associated with this theory, the origin of Dalton's atomic theory is not fully understood. The theory may have been suggested to him either by researches on ethylene and methane or by analysis of nitrous oxide and nitrogen dioxide, both views resting on the authority of Thomas Thomson.
From 1814 to 1819, Irish chemist William Higgins claimed that Dalton had plagiarised his ideas, but Higgins' theory did not address relative atomic mass. Recent evidence suggests that Dalton's development of thought may have been influenced by the ideas of another Irish chemist Bryan Higgins, who was William's uncle. Bryan believed that an atom was a heavy central particle surrounded by an atmosphere of caloric, the supposed substance of heat at the time. The size of the atom was determined by the diameter of the caloric atmosphere. Based on the evidence, Dalton was aware of Bryan's theory and adopted very similar ideas and language, but he never acknowledged Bryan's anticipation of his caloric model. However, the essential novelty of Dalton's atomic theory is that he provided a method of calculating relative atomic weights for the chemical elements, which provides the means for the assignment of molecular formulas for all chemical substances. Neither Bryan nor William Higgins did this, and Dalton's priority for that crucial innovation is uncontested.
A study of Dalton's laboratory notebooks, discovered in the rooms of the Manchester Literary and Philosophical Society, concluded that Dalton was not led by his search for an explanation of the law of multiple proportions to the idea that chemical combination consists in the interaction of atoms of definite and characteristic weight, but rather the idea of atoms arose in his mind as a purely physical concept, forced on 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 by Water and other Liquids" already mentioned. There he says:
He then proposes relative weights for the atoms of a few elements, without going into further detail. However, a recent study of Dalton's laboratory notebook entries concludes he developed the chemical atomic theory in 1803 to reconcile Henry Cavendish's and Antoine Lavoisier's analytical data on the composition of nitric acid, not to explain the solubility of gases in water.
The main points of Dalton's atomic theory, as it eventually developed, are:
  1. Elements are made of extremely small particles called atoms.
  2. Atoms of a given element are identical in size, mass and other properties; atoms of different elements differ in size, mass and other properties.
  3. Atoms cannot be subdivided, created or destroyed.
  4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
  5. In chemical reactions, atoms are combined, separated or rearranged.
In his first extended published discussion of the atomic theory, Dalton proposed an additional "rule of greatest simplicity". This rule could not be independently confirmed, but some such assumption was necessary in order to propose formulas for a few simple molecules, upon which the calculation of atomic weights depended. This rule dictated that if the atoms of two different elements were known to form only a single compound, like hydrogen and oxygen forming water or hydrogen and nitrogen forming ammonia, the molecules of that compound shall be assumed to consist of one atom of each element. For elements that combined in multiple ratios, such as the then-known two oxides of carbon or the three oxides of nitrogen, their combinations were assumed to be the simplest ones possible. For example, if two such combinations are known, one must consist of an atom of each element, and the other must consist of one atom of one element and two atoms of the other.
This was merely an assumption, derived from faith in the simplicity of nature. No evidence was then available to scientists to deduce how many atoms of each element combine to form molecules. But this or some other such rule was absolutely necessary to any incipient theory, since one needed an assumed molecular formula in order to calculate relative atomic weights. Dalton's "rule of greatest simplicity" caused him to assume that the formula for water was OH and ammonia was NH, quite different from our modern understanding. On the other hand, his simplicity rule led him to propose the correct modern formulas for the two oxides of carbon. Despite the uncertainty at the heart of Dalton's atomic theory, the principles of the theory survived.

Relative atomic weights

Dalton published his first table of relative atomic weights containing six elements, relative to the weight of an atom of hydrogen conventionally taken as 1. Since these were only relative weights, they do not have a unit of weight attached to them. Dalton provided no indication in this paper how he had arrived at these numbers, but in his laboratory notebook, dated 6 September 1803, is a list in which he set out the relative weights of the atoms of a number of elements, derived from analysis of water, ammonia, carbon dioxide, etc. by chemists of the time.
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 deduction. In the paper "On the Proportion of the Several Gases in the Atmosphere", read by him in November 1802, the law of multiple proportions appears to be anticipated in the words:
But there is reason to suspect that this sentence may have been added some time after the reading of the paper, which was not published until 1805.
Compounds were listed as binary, ternary, quaternary, etc. in the New System of Chemical Philosophy depending on the number of atoms a compound had in its simplest, empirical form.
Dalton hypothesised 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 atoms of element Y or vice versa, is a ternary compound. Many of the first compounds listed in the New System of Chemical Philosophy correspond to modern views, although many others do not.
Dalton used his own symbols to visually represent the atomic structure of compounds. They were depicted in the New System of Chemical Philosophy, where he listed 21 elements and 17 simple molecules.

Other investigations

Dalton published papers on such diverse topics as rain and dew and the origin of springs ; on heat, the colour of the sky, steam and the reflection and refraction of light; and on the grammatical subjects of the auxiliary verbs and participles of the English language.

Experimental approach

As an investigator, Dalton was often content with rough and inaccurate instruments, even though better ones were obtainable. 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." On the other hand, historians who have replicated some of his crucial experiments have confirmed Dalton's skill and precision.
In the preface to the second part of Volume 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 unconventional views on 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 Jacob Berzelius, although most thought that it was much simpler and more convenient than his own cumbersome system of circular symbols.

Other publications

For Rees's Cyclopædia Dalton contributed articles on Chemistry and Meteorology, but the topics are not known.
He contributed 117 Memoirs of the Literary and Philosophical Society of Manchester from 1817 until his death in 1844 while president of that organisation. 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 researchers. In 1840 a paper on 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 contain his discovery, regarded by him as second in importance only to 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.

Public life

Even before he had propounded the atomic theory, Dalton had attained a considerable scientific reputation. In 1804, he was chosen to give a series of lectures on natural philosophy at the Royal Institution in London, and he delivered another series of lectures there in 1809–1810. Some witnesses reported that he was deficient 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, Sir Humphry Davy asked him to offer himself as a candidate for the fellowship of the Royal Society, but Dalton declined, possibly for financial reasons. 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, Earl Grey's government conferred on him a pension of £150, raised in 1836 to £300. Dalton was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1834.
A young James Prescott Joule, who later studied and published on the nature of heat and its relationship to mechanical work, was a pupil of Dalton in his last years.

Personal life

Dalton never married and had only a few close friends. As a Quaker, he lived a modest and unassuming personal life.
For the 26 years prior to his death, Dalton lived in a room in the home of the Rev W. Johns, a published botanist, and his wife, in George Street, Manchester. Dalton and Johns died in the same year.
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.

Disability and death

Dalton suffered a minor stroke in 1837, and a second in 1838 left him with a speech impairment, although he remained able to perform experiments. In May 1844 he had another stroke; on 26 July, while his hand was trembling, he recorded his last meteorological observation. On 27 July, in Manchester, Dalton fell from his bed and was found dead by his attendant.
Dalton was accorded a civic funeral with full honours. His body lay 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. He was buried in Manchester in Ardwick Cemetery; the cemetery is now a playing field, but pictures of the original grave may be found in published materials.

Legacy

Works