# What is the Law of Definite Proportions?

#### Spiegazione:

The "law of definite proportions" o il "law of constant composition" holds that a chemical compound always contains its component elementi in a fixed ratio, regardless of the source of the compound. Joseph Proust proposed a similar "law of constant composition."

An example of this law is that water ALWAYS has a composition by mass of 1/8 hydrogen, and 7/8 oxygen. This law allows us to propose empirical formulae, and by extension molecular formulae, if the molecular mass is known.