John Dalton (1766-1844) was an English Chemist. His work was largely responsible for resurrecting the discarded Greek notion that the atom is the smallest, irreducible part of elements. He therefore contributed to our modern understanding of the elements, the atomic theory, and quantum mechanics. He also made some useful contributions in understanding color blindness in people.
“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 pressure exerted upon the unmixed gases further.”
Dalton demonstrated how water is turned into vapor (gas) and under what temperature (pressure) that takes place. Exertion of heat transforms water and other liquids to gas. Gas, in turn, can be reconverted to liquid by cooling it.
Dalton further showed that the absorption of gases by water and other liquids is due partially to pressure.
These observations came to be called Dalton’s law.
Dalton’s most revolutionary contribution to science, however, is his atomic theory. In 1803 he wrote:
“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.”
That is to say that Dalton recognized that elements exist as atoms, and that different elements are characterized by their weights. He gave atomic weights to six elements: hydrogen, oxygen, nitrogen, carbon, sulfur, and phosphorus.
He gave hydrogen’s weight as one (1). How he reached this conclusion he did not explain. However, what is critical is what he said next: he concluded that chemical combinations take place between particles of different weights.
This idea was later expanded to his law of multiple proportions (which states that gases combine in an ascertainable proportional manner) as in the statement: “The elements of oxygen may combine with certain portion of nitrous gas or with twice that portion, but with no intermediate quantity.”
Later, Dalton listed the compounds formed by combining gases as either binary (molecules composed of two atoms), or ternary (molecules composed of three atoms), quaternary (molecules composed of four atoms) and so on.
Dalton speculated that the structure of compounds can be represented in whole numbers (an atom of X element combining with one atom of Y element is a binary compound etc).
In his book, New Systems of Chemical Philosophy, Dalton explicated his new atomic theory as follows:
Elements are made of atoms (which in his view were irreducible to other forms).
All atoms of a given element are identical.
The atoms of a given element are different from the atoms of other elements (distinguished by their atomic weights).
The atoms of one element can combine with the atoms of other elements (to form compounds).
Atoms cannot be created or destroyed in chemical procedures; chemical reactions merely change how the atoms are arranged together.
Obviously Dalton was wrong in stating that atoms cannot be reduced to smaller particles. Nuclear reactions, as opposed to the chemical reactions he knew about, have shown how atoms can be split into particles, such as electrons, neutrons and protons. Indeed, particles can be further split into sub-particles such as quarks and neutrinos etc.
This correction not withstanding, Dalton’s resurrection of the discarded Greek notion that elements are composed of atoms is a revolutionary improvement in the study of physics and chemistry.
Dalton made enormous contribution to chemistry, especially to our understanding of acids, bases, salts and varieties thereof.
Clearly, Dalton contributed to empirical science, especially experimental science. Though by today’s standards his experiments were crude yet he blazed the trail and contributed to our understanding of the various elements, their weights and valences.
Like many scientists, Dalton’s social skills were not the best. He never married and lived with relatives all his life.
John Dalton. The New System of Chemical Philosophy. (1803)
Elizabeth Patterson. John Dalton and the Atomic Theory. (New York: Anchor, 1970)