9 августа 1776 года родился химик Амедео Авогадро

Lorenzo Romano Amedeo Carlo Avogadro Count Cuarena y Cerreto was born into a family of hereditary lawyers. He did not continue the dynasty, though he did become the author of the law. Unlike legal laws, this one is known by anyone who studied chemistry thoroughly: under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of molecules.

What number? Avogadro did not give the answer to this question, it was done without him, although they gave the physical constant his name. Avogadro's number is the number of molecules in one mole of any substance. With the development of scientific methods, this constant is constantly being tweaked. In 2010, the Committee on Data for Science and Technology of the International Council for Science (CODATA) recommended that the value of Avogadro's number be taken as NA=6,02214129(27)·1023mol−1.

Hard to remember? Well, it actually9 isn't: American chemists celebrate Amedeo Avogadro Memorial Day on October 23. They distinguished the 23rd of the 10th month as 10 to the 23rd power. But 6.022 and minus first degree of a mole will still have to be memorized.