Question

Note: I am not a chemist, I am just interested in this

Proust famously compared the mass composition by element of natural and artificially prepared copper carbonate and concluded they were the same, but-

Since this is early atomic hypothesis days, how did he know to compare Cu, O and C and not Cu and CO2 or something ie. how did he know what the elements were?

I assume he determined mass composition of the artificial carbonate by measuring the elements he used to prepare them (a equation of what he did would be helpful), but how did he measure composition of the naturally occurring carbonates, don't the reactions for their breakdown leave compounds behind that are not easy to decompose to elements, and then he had to somehow separate and weigh them all

Answer 1

Proust compared the mass composition of copper carbonate in its natural and artificial forms by a method that relied on the early 19th-century understanding of elements. Techniques to determine these compositions included heating and chemically treating the compounds to analyze them individually.

Step-by-step explanation:

Joseph Proust's experiments in the early 19th century played a foundational role in establishing the law of definite proportions. Proust compared the mass composition of copper carbonate both in its natural form and when prepared artificially.

Proust determined the mass composition of artificially prepared copper carbonates by measuring the elements he used in their synthesis. For natural carbonates, the processes likely involved heating or treating the compound chemically to break it down into simpler substances, which could then be individually analyzed. Through repeated experimentation, Proust could deduce the constant proportion by mass of Cu, O, and C in copper carbonate.