Proust’s Law


Proust’s law is one that expresses that the relative number of elements formed within a compound, are kept constant, regardless of the origin of said compound. This law was first proposed by the French-born chemist Louis Proust in 1795.

Proust carried out a large part of his research in Spain and it is there that he manages to determine that the mixture of elements can be carried out in a continuous weight relationship regardless of the immediate process that formed it. That is, the elements that make up a compound will maintain a fixed proportion by weight, within any net sample of a mixture. A simple example of this law is the case of water, it is made up of two elements: hydrogen and oxygen, which will always be in a ratio of 1-8, regardless of the origin of the water.

Through this law Proust also showed that the theory of the chemist Berthollet was incorrect, since he claimed that some chemical mixtures could vary in their composition, depending on the way they were prepared. Proust attributed this mistake to the misuse of chemical substances that were not completely purified. Proust’s success was more than evident and his theory was definitively established, thanks to the support of another chemist named Jons Berzelius, who supported his hypothesis, which was unanimously accepted.

Proust’s law guaranteed proportionality between the mass of reactive substances and the products in a chemical reaction. This is why it was also known as the law of definite proportions.

For the industry and laboratory environment, these laws are very useful in calculating the amount of reagents needed to prepare substances, as well as the number of products that must be produced.