I was reading chapter 3 of The Capital vol. 1.
So, as far as I understand it, Marx is laying the groundwork for understanding capital. It's easy to see this by how money kind of "outlasts" the commodities being exchanged. It keeps circulating even when commodities are consumed.
However, I kind of don't understand why Marx starts to talk about gold in the section The Currency of Money.
long quotes
[...] Money, on the contrary, as the medium of circulation, keeps continually within the sphere of circulation, and moves about in it. The question therefore arises, how much money this sphere constantly absorbs?
In a given country there take place every day at the same time, but in different localities, numerous one-sided metamorphoses of commodities, or, in other words, numerous sales and numerous purchases. The commodities are equated beforehand in imagination [...]
As a matter of fact, the money in reality represents the quantity or sum of gold ideally expressed beforehand by the sum of the prices of the commodities. [...] We know, however, that, the values of commodities remaining constant, their prices vary with the value of gold. (Why mention this?)
Maybe it's the fact that bourgeois education taught me to treat money strictly as an abstract thing so I can't the connection, but I don't know why Marx decided to mention gold here when we are talking about price and circulation.
I'll try to read it again tomorrow.
Edit: I got it