Early life
John Dalton was born into a Quaker family at the settlement of Eaglesfield, near the town of Cockermouth, in the county of Cumberland, England in 1766.[1] His father was a weaver. He received his early education from his father and from Quaker John Fletcher, who ran a private school at 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 local Quaker, Elihu Robinson.[2][3] It is said he began teaching at a local school at age 12, and was prolific in Latin at age 14.
Early careers
He joined his older brother Jonathan at age 15 in running a Quaker school at Stramongate in Kendal, about forty five miles from his home.[2] Around age 23 Dalton may have considered studying law or medicine, but his relatives did not encourage him, perhaps because being a Dissenter (a Christian opposed to a state religion and mandatory membership in the Church of England), 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. At age 27 he was appointed teacher of mathematics and natural philosophy at the "New College" in Manchester, a dissenting academy. 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.
Scientific contributions
Meteorology
Dalton's early life was highly influenced by a prominent Eaglesfield Quaker named Elihu Robinson,[4] a competent meteorologist and instrument maker, who got him interested in problems of mathematics and meteorology. During his years in Kendal, Dalton contributed solutions of problems and questions on various subjects to The Ladies' Diary and the Gentleman's Diary. In 1787 at age 21 he began to keep a meteorological diary in which, during the succeeding 57 years, he entered more than 200,000 observations.[5] He also rediscovered George Hadley's theory of atmospheric circulation (now known as the Hadley cell) around this time.[6] Dalton's first publication was Meteorological Observations and Essays at age 27 in 1793, which contained the seeds of several of his later discoveries. However, in spite of 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 at age 35 in 1801.
Colour blindness
In 1794 at age 28, 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. In fact, a shortage of colour perception in some people had not even been formally described or officially noticed until Dalton wrote about his own.[citation needed] Since both he and his brother were colour blind, he recognized that this condition must be hereditary.[7]
Although Dalton's theory lost credence in his own lifetime, the thorough and methodical nature of his research into his own visual problem was so broadly recognized that Daltonism became a common term for colour blindness.[8] 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 (rather than functioning with a mutated form of their pigment, as in the most common type of colour blindness, deuteroanomaly).[7] Besides the blue and purple of the optical 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
Measuring mountains in the Lake District
Dalton regularly holidayed in the Lake District where his study of meteorology involved a lot of mountain climbing: 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. The altitude achieved was estimated using a barometer. This meant that, until the Ordnance Survey started publishing their maps for the Lake District in the 1860s, Dalton was one of the few sources of such information.[9] Dalton was often accompanied by Jonathan Otley, who was one of the few other authorities on the heights of the Lake District mountains. He became both an assistant and a friend.[10]
Gas laws
External video
Dalton John profile.jpg
Profiles in Chemistry:How John Dalton's meteorological studies led to the discovery of atoms on YouTube, Chemical Heritage Foundation
In 1800, at age 34 Dalton became a secretary of the Manchester Literary and Philosophical Society, and in the following year he orally presented an important series of papers, entitled "Experimental Essays" on the constitution of mixed gases; on the pressure of steam and other vapours at different temperatures, both in a vacuum and in air; on evaporation; and on the thermal expansion of gases. These four essays were published in the Memoirs of the Lit & Phil in 1802.
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 effecting 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), Dalton concluded from observations on 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,[11]
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 or J.A.C. Charles's law, published in 1802 at age 36 by Joseph Louis Gay-Lussac. In the two or three years following the reading of these essays, Dalton published several papers on similar topics, that on the absorption of gases by water and other liquids (1803), containing his law of partial pressures now known as Dalton's law.
Atomic theory
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 & Phil,[12] concluded that so far from Dalton being 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, the idea of atoms 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 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.
The main points of Dalton's atomic theory were:
Elements are made of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
In chemical reactions, atoms are combined, separated, or rearranged.
Dalton proposed an additional "rule of greatest simplicity" that created controversy, since it could not be independently confirmed.
When atoms combine in only one ratio, "..it must be presumed to be a binary one, unless some cause appear to the contrary".
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 compound 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. In any case, 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 (H2O, NH3).
Despite the uncertainty at the heart of Dalton's atomic theory, the principles of the theory survived. To be sure, the conviction that atoms cannot be subdivided, created, or destroyed into smaller particles when they are combined, separated, o