This law was opened by the Italian chemist Amedeo Avogadro. It was preceded by enough lot of work of one more scientist - Gay-Lussac which helped Avogadro to open the law connecting the volume of gas and quantity of the molecules which are contained in it.
In 1808 the French physicist and the chemist Gay-Lussac studied one plain chemical reaction. Interaction was entered by two gases: chlorohydrogen and ammonia owing to what solid crystal substance - ammonium chloride was formed. The scientist noticed something unusual: that reaction was carried out, the identical amount of both gases is required. The surplus of any of gases just will not react with other gas. At a lack of one of them the reaction will not proceed at all.
Gay-Lussac studied also other interactions between gases. In any reactions the interesting regularity was observed: the amount of the gases which reacted has to be or is identical, or to differ in an integer of times. For example, mix of one part of oxygen with two parts of hydrogen forms water vapor if in a flask to make rather powerful explosion.
Gay-Lussac did not try to find out why reactions proceed only with the gases taken in certain ratios. Avogadro studied his works and made a hypothesis that equal volumes of gases contain the same number of molecules. Only in this case all molecules of one gas could react with molecules of another, the surplus (if that was available) did not enter interaction. This hypothesis was confirmed by numerous experiments which were made by Avogadro. The final wording of its law sounds so: equal volumes of gases at identical temperatures and pressure contain the same quantity of molecules. It is defined by Avogadro's number of Na which is equal 6.02*1023 molecules. This size is used for the solution of numerous gas tasks. This law does not work in case of solid bodies and liquids. In them, unlike gases, much more powerful forces of intermolecular interaction are observed.
The investigations from Avogadro's law
From this law very important statement follows. The molecular mass of any gas has to be proportional to its density. It turns out that M=K*d where M - molecular weight, d - density of the corresponding gas, and K - a certain coefficient of proportionality.K is identical to all gases which are on an equal footing. It is equal to about 22.4 l/mol. It is very important size. It shows the volume which occupies one mol of gas under normal conditions (temperature of 273 K or 0 degrees Celsius and pressure of 760 mm Hg). It is quite often called the molar volume of gas.