It states that matter can neither be created nor destroyed.

This law was put forth by Antoine Lavoisier in 1789. He performed careful experimental studies for combustion reactions for reaching to the above conclusion. This law formed the basis for several later developments in chemistry.

Lavoisier stated that "during any physical or chemical change the total mass of the products produced is equal to the total mass of the reactants reacted" . He showed that when mercuric oxide was heated the total mass of mercury and oxygen produced was equal to the total mass of mercuric oxide.

This law was given by, a French chemist, Joseph Proust. He stated that a given compound always contains exactly the same proportion of elements by weight.

Irrespective of the source, a given compound always contains same elements in the same proportion. The validity of this law has been confirmed by various experiments. It is sometimes also referred to as Law of definite composition .

This law implies that irrespective of how a compound is prepared or from where the compound originates, it is always made up of the same elements combined in the same proportion by the weight.

For example, if water is taken from difference sources, such as rivers, oceans, wells etc. they all contain hydrogen and oxygen, combined in the same proportion by weight in it.

This law was proposed by Dalton in 1803. According to this law, if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers.

For example , carbon and oxygen combine to form `CO` and `CO_2`. In `CO`, `12` parts by mass of carbon combines with `16` parts by mass of oxygen while in `CO_2`, `12` parts by mass of carbon combines with `32` parts by mass of oxygen. Therefore, the ratio of the masses of oxygen that combines with a fixed mass of carbon is `16:32` that is `1 :2`.

This law which was proposed by Ritcher (1792) states that "when two elements combine separately with fixed mass of third element then the ratio of their masses in which they do so is either the same or some whole number multiple of the ratio in which they combine with each other".

This law which was proposed by Gay-Lussac states that, the volumes of gaseous reactants reacted and the volumes of gaseous products formed, all measured at the same temperature and pressure bear a simple ratio.

This law is applicable only for gaseous reactions and should not be used for non-gaseous reactants and products.