JOHN DALTONJohn Dalton FRS (6 September 1766 – 27 July 1844) was an English chemist,

physicist, and meteorologist. 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 honor.

Born : 6 September 1766 Eagles field, Cumberland, England

Died : 27 July 1844 (aged 77) Manchester, England

Nationality : British

Notable students : James Prescott Joule

Known for : Atomic theory, Law of Multiple Proportions, Dalton's Law of Partial Pressures, Daltonism

Notable awards : Royal Medal (1826)

Author abbrev. : Jn.Dalton

Scientific contributionsGas lawsIn 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 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), Dalton concluded from observations on the

vapour pressure of six different liquids, that the variation of vapor 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

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. While his name is inseparably associated with this

theory, the origin of Dalton's atomic theory is not fully understood 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 azotes), 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, 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.1. Atoms of a given

element are identical in size, mass, and other properties; atoms of different

elements differ in size, mass, and other properties. 2. Atoms cannot be subdivided,

created, or destroyed.3. Atoms of different elements combine in simple whole-

number ratios to form chemical compounds.4. In chemical reactions, atoms are

combined, separated, or rearranged.5.

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 appears 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, or

rearranged in chemical reactions is inconsistent with the existence of nuclear

fusion and nuclear fission, but such processes are nuclear reactions and not

chemical reactions. In addition, the idea that all atoms of a given element are

identical in their physical and chemical properties is not precisely true, as we now

know that different isotopes of an element have slightly varying weights. However,

Dalton had created a theory of immense power and importance. Indeed, Dalton's

innovation was fully as important for the future of the science as Antoine Laurent

Lavoisier's oxygen-based chemistry had been.

Atomic weights

Dalton proceeded to print his first published table of relative atomic weights. Six

elements appear in this table, namely hydrogen, oxygen, nitrogen, carbon, sulfur,

and phosphorus, with the atom of hydrogen conventionally assumed to weigh 1.

Dalton provided no indication in this first paper how he had arrived at these

numbers. However, in his laboratory notebook under the date 6 September 180]

there appears a list in which he sets 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.

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 it

was this which differentiated his theory from the historic speculations of the

Greeks, such as Democritus and Lucretius.

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. 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 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. (molecules composed of

two, three, four, etc. atoms) 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 correspond to modern views,

although many others do not.

Dalton used his own symbols to visually represent the atomic structure of

compounds. These were depicted in the New System of Chemical Philosophy,

where Dalton listed twenty elements and seventeen simple molecules.

Experimental approach

As an investigator, Dalton was often content with rough and inaccurate

instruments, even though better ones were obtainable. Sir Humphrey 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 Jones Jacob Berzelius,

although most thought that it was much simpler and more convenient than his own

cumbersome system of circular symbols.

Legacy

A bust of Dalton, by Chantrey, was publicly subscribed for and placed in the

entrance hall of the Royal Manchester Institution. Chantrey also crafted a large

statue of Dalton: it was erected while Dalton was still alive and it has been said:

"He is probably the only scientist who got a statue in his lifetime". It was placed in

Manchester Town Hall after its construction in 1877 and remains there today.

In honor of Dalton's work, many chemists and biochemists use the (as yet

unofficial) designation Dalton (Abbreviated Da) to denote one atomic mass unit

(1/12 the weight of a neutral atom of carbon-12).

There is a John Dalton Street connecting Deansgate and Albert Square in the centre

of Manchester.

Manchester Metropolitan University named a building after John Dalton; it is

occupied by the Faculty of Science and Engineering. A statue of Dalton, the work

of William Themed, was erected in Piccadilly in 1855, and moved in 1966 to

outside this building.

The University of Manchester has a hall of residence called Dalton Hall; it also

established two Dalton Chemical Scholarships, two Dalton Mathematical

Scholarships, and a Dalton Prize for Natural History. There is a Dalton Medal,

awarded thus far only twelve times by the Manchester Literary and Philosophical

Society.

Dalton Township in southern Ontario was named for Dalton. It 2001 the name was

lost when the township was absorbed into the City of Kawartha Lakes; however in

2002 the Dalton name was affixed a massive new park there: Dalton Dig by Wild

lands Provincial Park.

A lunar crater was named after Dalton.

"Daltons" became a common term for color blindness and "Daltonien" is the actual

French word for "color blind".

The inorganic section of the UK's Royal Society of Chemistry is named after

Dalton (Dalton Division), and the Society's academic journal for inorganic

chemistry also bears his name (Dalton Transactions).

Many Quaker schools name buildings after Dalton: for example, one of the school

houses in Coram House, the primary sector of Acworth School, is called Dalton.

Much of his written works were collected at the Manchester Literary and

Philosophical Society, but were damaged during a bombing on 24 December 1940.

This event prompted Isaac Asimov to say, "John 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 is killed in war". The damaged papers are

now in the John Ryland’s Library.