A vogadro was born on June 9, 1776 in Turin, Italy. He began his career in 1796 by obtaining a doctorate in law and practicing as a lawyer for three years after. In 1800, he began to take private lessons in mathematics and physics and decided to make the natural sciences his profession. He was appointed as a demonstrator at the Academy of Turin in1806 and the Professor of Natural Philosophy at the College of Vercelli in 1809, and in 1820, he was appointed the professor of mathematical physics. He was a physics professor but he also experimented in chemistry using mathematics to base most of his findings. Avogadro is well known for his hypothesis known as Avogadro's Law. His law states that at a given temperature, equal volumes of gas contain the same number of molecules equal to about 6.0221367 x 10 to the 23rd power.A Mole of a substance is the quantity of the substance that weights the same as its molecular mass. One mole of any substance is Equal to Avogadro's number. Therefore Avogadro's law can be stated in terms of moles, namely that equal volumes of gases at the same temperature and pressure contain the same number of moles. Thanks to Avogadro and his number, scientists can measure out equal number of molecules by weighing out an equal number of moles. For gases this can be done by using 22.4 liters at STP(1 atmosphere and 223 Kelvin, 0 deg. Celsius). Avogadro's number is most reliably determined by X-ray diffraction of crystals. For many years' people thought the number was equal to about 6.022045 x 10 to the 23rd power, However, in 1986 the number was redefined as about 6.0221367 x 10 to the 23rd power.Albert Einstein's third research paper was concerned with the nature of molecules. We all know that if we drop a lump of sugar into water it diffuses through the water, making it somewhat more sticky. Thinking of water as a structureless fluid and the sugar molecules as small hard spheres, Einstein was able to find not only the size of the sugar molecules but also a value for Avogadro's number. Avogadro proposed his hypothesis in 1811. At that time there was no data at all on the number of particles in a mole. Measurements were made by Robert Brown in 1827 that gave an approximate value for Avogadro's number by observations of brownian motion. Cannizarro later used Avogadro's hypothesis to develop a set of atomic weights based on 116 of the weight of oxygen. This was a basis for finding much more accurate estimates for Avogadro's number. Reasonable values were made in the late 1800's from sedimentation equilibrium of colloidal particles. Millikan's oil drop experiment in the 1900's gave even more accuracy and was cited in most chemistry text books 50 years ago. Text books in 1958 gave Avogadro's number as 6.02 x10 to the 23rd. The current value is 6.0221367x10 to the 23rd power. Amedeo Avogadro proved to be one of the greatest scientists to ever live. If it had not been for Avogadro and his findings there is no way that Chemistry in general would be where it is today. Avogadro's work was recognized nearly fifty years after he had made his hypothesis. Two years after his death, his colleague showed how they could use Avogadro's number to solve many of the problems in chemistry. Avogadro's work also helped other scientists to solve more problems and develop more theories.

**Bibliography:**

- Asimov, Isaac, A Short History of Chemistry (1965; repr. 1979);
- Morselli, Mario, Amadeo Avogadro (1984);-Partington, J. R., A History of Chemistry, vol. 4 (1964)
- Atomic Masses and Fundamental Constants (1980);
- Rossini, F. D., Fundamental Measures and Constants for Science and Technology (1974)