Here is a description of an analytical procedure for superconductors containing unknown quantities of Cu(I), Cu(II), Cu(III), and peroxide (O₂^2-):³² "The possible trivalent copper and/or peroxide-type oxygen are reduced by Cu(I) when dissolving the sample (ca. 50 mg) in deoxygenated HCl solution (1 M) containing a known excess of monovalent copper ions (ca. 25 mg CuCl). On the other hand, if the sample itself contained monovalent copper, the amount of Cu(I) in the solution would increase upon dissolving the sample. The excess Cu(I) was then determined by coulometric back-titration . . . in an argon atmosphere." The abbreviation "ca." means "approximately." Coulometry is an electrochemical method in which the electrons liberated in the reaction Cu⁺ → Cu²⁺ + e^- are measured from the charge flowing through an electrode. Explain with your own words and equations how this analysis works.