What is the Law of Definite Proportions?

Proust's law strictly states that: "In a pure chemical compound, the elements are ALWAYS combined together in exactly the same fixed ratio by mass, regardless of where the compound was found or how it was created."

This means Mother Nature follows a strict mathematical recipe. If you change the ratio of the atoms even by a tiny 1%, the magic fails, and you will accidentally create a completely different, potentially deadly chemical.

Let us aggressively prove this law using pure Water (H₂O).

• A water molecule has 2 Hydrogen atoms (mass = 1 each, total = 2) and 1 Oxygen atom (mass = 16).
• The strict ratio by mass of Hydrogen to Oxygen is 2:16, which perfectly simplifies down to 1:8.

Proust's Law means that if you collect a cup of pure water from a dirty river in India, melt a block of ice from Antarctica, or synthetically create water in a NASA laboratory, the mass ratio of Hydrogen to Oxygen will ALWAYS, mathematically, be exactly 1:8. It never changes.

If you look at Carbon Dioxide (CO₂):

• Mass of Carbon = 12.
• Mass of Oxygen = 16 × 2 = 32.
• The strict mass ratio is 12:32, which simplifies to 3:8. Whether the CO₂ comes out of a massive car exhaust or from your lungs when you breathe, the ratio is permanently locked at 3:8.