867. When an assignment of after-acquired property is effective.

An assignment of after-acquired property, when made for valuable consideration1, operates in equity as a contract which is enforceable against the assignor, and which, as soon as he acquires property which can be identified as that comprised in the assignment, becomes an equitable charge upon that property2. As soon as the assignor acquires the legal interest, the equitable interest passes to the assignee, equity treating as done that which ought to be done