John Dalton, the son of a poor weaver, was born in Cumberland, England. He first studied at a village school, and he made such rapid progress that by the age of twelve he became the teacher at the school. Seven years later he became a school principal.In 1793 he moved to Manchester, and he remained there for the rest of his life. He first taught mathematics, physics, and chemistry at a college. But finding that his teaching duties interfered with his scientific studies, he resigned from this post and supported himself by teaching mathematics and chemistry to private pupils. He never married. He continued to live a very simple and modest life even after he became famous.
Dalton’s first scientific investigations were in meteorology. Throughout his life, he continued to make daily observations on the temperature, barometric pressure, and rainfall. He described the nature of colour blindness, of which he was a victim. A devout Quaker, Dalton always wore plain and somber clothes. Friends were therefore surprised when he wore a scarlet academic robe on being presented to King William IV in 1832. To Dalton, however, it appeared a dull gray, and he wore it without concern.
Dalton put forward his atomic theory in 1803. He proposed that compounds were formed by the combination of atoms of different elements in small, whole-number ratios. However, he had no certain method for determining the ratios in which the different atoms combine. He assumed therefore, when only one compound of two elements A and B was known, that it had the simplest possible formula, AB. On the basis of this assumption and from the masses of different elements that were found to combine, he was able to deduce relative atomic masses. He published the first table of such relative atomic masses.
His assumptions about formulas of compounds, however, were not always valid. For example, he assumed that the formula of water was HO, which led to some incorrect atomic masses in his table. In fact, not until 1858 did chemists solve the problem of the determination of molecular formulas and therefore of atomic masses. Nevertheless, the credit must go to Dalton for first putting the atomic theory on a quantitative basis and for laying the foundation for the rapid development of chemistry.
