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(Eaglesfield, Britain, 1766 - Manchester, 1844) British physicist and chemist to which the first modern formulation of the atomic theory. Despite receiving a poor education because of economic hardships, an inexhaustible curiosity and desire for knowledge allowed him to complete his training and get some prestige with his first scientific work, which centred on gases and a visual illness that he suffered, later called Daltonism.
John Dalton (portrait by Thomas Phillips, 1835)
Already recognized as a scientist and a strong academic position, Dalton discovered the so-called law of multiple proportions, governing the weight of the elements involved in a chemical reaction, and proposed a whole theory on the Constitution of matter that resumed Greek atomism as interpretation of it: is the so-called atomic model of Dalton, to valid throughout the 19th century, would enable important scientific advances.
Member of a very humble family, his childhood helped with his brother to his father in the field work and the small family shop where they wove dresses, while his sister Mary helped her mother in the household chores and sold paper, ink, and pens. Although their economic situation was precarious, the brothers received some education at school Quaker nearest, unlike other children of the same condition.
Pardshow Hall Quaker school teacher John Dalton provided a good basis and transmitted to him the desire by the tireless pursuit of new knowledge. A wealthy Quaker, Elihu Robinson, became his mentor and another source of stimulus towards mathematics and Sciences (especially meteorology). With only twelve years of age, John Dalton opened a school in his hometown, Eaglesfield. Although he knew how to handle problems with students older than him, after two years he was forced to abandon the project due to the low wage, and had to return to the field working for an uncle.
In 1781 John Dalton joined his brother as an Assistant of George Bewley in its school of Kendall. When George Bewley retired, his brother and he opened his own school, which offered classes in English, latin, Greek and French, in addition to twenty-one topics related to mathematics and the sciences. His sister moved with them to help them in the House. Despite having about sixty students, they were sometimes forced to work in auxiliary tasks to keep.
John Gough, the blind a rich merchant's son, became a friend of John Dalton and became his new mentor. He taught languages, mathematics, and optics, as well as share your library with Dalton. Dalton interest extended to pneumatics, astronomy and geography, and in 1787 began to earn extraordinary income giving lectures. It also turned to a nearby Museum offering to sell classified eleven volumes of his botanical collection. He collected butterflies and studying the snails, ticks and worms; It also measured their intake of foods and compared it with the waste produced by the body. At the same time preparing its entry into medical school, but his family discouraged it for lack of money and of trust in him.
At the age of 26 years, Dalton discovered that neither he nor his brother were able to distinguish colors. He gave his mother stockings (which he believed blue) and she asked surprised why had given you a medium purple, color that was not appropriate for a Quaker woman. Two years later, in his first important scientific article, extraordinary facts relating to the vision of colours (1794), John Dalton would provide a scientific description on this phenomenon, which would later become known with the name of color blindness.
A year earlier, in 1793, Dalton had published his first book, observations and meteorological essays, where he defended the thesis that the air is not a chemical combination, but a merely physical mixture of gases. That same year he moved to Manchester as tutor and lecturer in physics and mathematics from New College in this city, founded by Presbyterians, and whose reputation then rivaled that of the universities of Oxford and Cambridge. She immediately enrolled in the library of Manchester and the literary and philosophical society that would become Secretary and President.
Professor and researcher
Those two scientific papers had provided him a certain notoriety, and, already with a looser economic situation, could alternate teaching with research in the laboratory. In 1802, entitled memory absorption of gases by water and other liquids, he established his law of partial pressures (Dalton's law), according to which the pressure of a gas mixture is equal to the sum of the pressures of each component. He also established a relationship between the vapour pressure and temperature. His interest in the gas was derived from their penchant to meteorological studies: always wearing their appliances of the time where would be doing more than two hundred thousand observations scoring in his diary throughout his life. Thanks to these observations, his analytical mind could find numerical relationships between data.
In 1803 he began to formulate his greatest contribution to science. He was studying the reaction of nitric oxide with oxygen when he discovered that the reaction could take place with two different proportions: sometimes 1: 1, 7 and other 1; 3.4 (by weight). This led to Dalton to establish the law of multiple proportions, according to which, in a chemical reaction, the weights of two elements always combine together in ratios of small whole numbers; looking for an interpretation to this phenomenon, he began sketching the principles of his atomic theory.
The results were communicated orally that same year and published in 1808 in a book that is his most famous work: new system of chemical philosophy. It adopted the notion of atom and established the postulates of the constitutive theory of matter that we know today as atomic theory of Dalton; drew individual particles to illustrate the chemical reactions and published its first list of atomic weights and symbols.
John Dalton (portrait by Thomas Phillips, 1835)
Not everyone accepted the new theory; in 1810 he published the second part of the new system of chemical philosophy, providing new empirical evidence. The third would see the light in 1827. Although he was a member of the Royal Society from 1822 and in 1825 received the Medal of this scientific society for his work on the atomic theory, Dalton has always considered himself himself as a teacher, and earned the life giving and lectured until 1833, when he was awarded an annual pension of civil.
On July 27, 1844 he died of a heart attack. According to his desire, after his death was practiced her autopsy to determine the cause of what would later be called Daltonism. It showed that the color blindness is not a problem of the eye, but it was caused by a deficiency of the sensory power. He was buried with honors from monarch, at a funeral followed by more than 400,000 people, contrary to the principles of the Quakers in accordance with those who had lived.
Dalton's atomic theory
The concept of atom goes back to discussions among the Greek philosophers developed around the 6th century B.c. One of the questions that interested these thinkers was the nature of the subject matter. Wondered if it was continuous or discontinuous, i.e.: if possible, from a piece of chalk as many times as you would like, would would be a particle that already could not continue dividing or, on the contrary, this process could continue indefinitely?
An advocate of the concept of last particle was the philosopher Democritus, who such particles called atoms. Atoms in Greek, means "indivisible." Such particles last debate was never resolved; the Greek philosophers not raised is to test their ideas with experiments. For over twenty centuries, the concept of Democritus was filed as something of interest secondary among scientists, until the idea was reborn in the first decade of the 19th century, at the hands of John Dalton.
John Dalton had not set out to formulate a theory on the Constitution of matter; She became as a result of his research on gases, and its objective was none other that explain the discoveries made in the same. In his memory, absorption of gases by water and other liquids (1802), had established his well known law of partial pressures: the total pressure exerted by a gaseous mixture is equal to the sum of the pressures of partial of each of its components.
A natural continuation of these studies was to investigate the composition of the same gases (and especially of oxides of nitrogen, the oxygen compounds of sulphur and carbon, methane, etc.). Repeated experiences would lead him to discover the law of multiple proportions: If two or more elements combine in a chemical reaction and the weight of one of them remains constant, the weight of others varies according to simple relationship expressed in integer multiples. Put another way, substances always react with each other keeping a constant relationship between their respective weights; they can be combined in large or small quantities, but that same ratio is always maintained.
To explain these arithmetic relations, John Dalton was that every element must be composed of specific amounts of matter, which made the existence of multiples of those understandable and they explained that only certain values of their weights intervene in a reaction. He thus returned to the atomic theory of Democritus, who considered the matter made up of indivisible particles. The existence of interatomic spaces, on the other hand, justified the compressibility of gases, state changes and the phenomenon of dilation, facts inexplicable if it did not note the discontinuity of matter.
October 21, 1803, Dalton first exhibited his atomic theory at a Conference in Manchester, organised by the literary and philosophical society before an audience of seven people. It is not surprising the lack of public, because Dalton had no reputation for good speaker. But his theory got more disclosure to publish it, in 1808, the first part of his work new system of chemical philosophy.
Dalton's atomic theory established a series of fundamental postulates: the elements are composed of atoms, tiny material particles that cannot be created, destroyed, or divided; all atoms of a given element are identical in mass and other properties; atoms are combined in proportions expressed in whole numbers, simple to form "compound atoms" (what today we call molecules, concept that would be introduced by Amadeo Avogadro); all "compound atoms" of the same substance are identical, both the mass and other properties.
The law of multiple proportions and Atomic hypothesis led to the same Dalton at the first attempt of making a basic tool for Chemistry instrument: a table of Atomic masses, which already appeared in the first part of the new system of chemical philosophy. Dalton chose hydrogen as a pattern for the table of Atomic masses and gave a mass of 1 atom of that element. Naturally, he could have chosen any other element and any other value for Atomic mass, but hydrogen was the lightest element and 1 is the number that allows you to make comparisons easier.
Table prepared by Dalton was incorrect for two main reasons: first, unaware of the correct relationship of combination of atoms in a chemical reaction, and secondly, the equipment used at the time to determine relations of masses was not very accurate. As a result, established values were significantly lower than the actual. However, his table was an important first step in determining the Atomic masses, and just twenty years later, the Swedish chemist Jöns Jacob Berzelius was already able to establish a list of Atomic masses with very similar to those currently accepted values.
Regarded as one of the foundations of modern science, Dalton's atomic theory would be revealed as a hypothesis extremely fruitful for both chemistry and physics, and remained in force for nearly a century. We had to wait for the discovery of subatomic particles (which ended with the dogma of the indivisibility of the Atom) to see substantial changes in the model, reflected in the successively perfected Atomic theories of Joseph John Thomson, Ernest Rutherford and Niels Bohr, already at the beginning of the 20th century.