Question: The proportionality of the amount of a substance to the quantity of electricity passed through is described by which law?
About the article "Electrochemistry", section "First law".

Candidate passages:
Beer’s law, also called Lambert–Beer law or Beer–Lambert law, in spectroscopy, is the physical law stating that the quantity of light absorbed by a substance dissolved in a nonabsorbing solvent is directly proportional to the concentration of the substance and the path length of the light through the solution.
Beer's law is commonly written in the form A = ε cl, where A is the absorbance, c is the concentration in moles per liter, l is the path length in centimeters, and ε is a constant of proportionality known as the molar extinction coefficient.
The law is accurate only for dilute solutions; deviations from the law occur in concentrated solutions because of interactions between molecules of the solute, the substance dissolved in the solvent. 
Faraday concluded after several experiments on electrical current in non-spontaneous process, the mass of the products yielded on the electrodes was proportional to the value of current supplied to the cell, the length of time the current existed, and the molar mass of the substance analyzed.
In other words, the amount of a substance deposited on each electrode of an electrolytic cell is directly proportional to the quantity of electricity passed through the cell.
Below is a simplified equation of Faraday's first law:
formula_7
Where
"m" is the mass of the substance produced at the electrode (in grams),
"Q" is the total electric charge that passed through the solution (in coulombs),
"n" is the valence number of the substance as an ion in solution (electrons per ion),
"M" is the molar mass of the substance (in grams per mole).
Faraday discovered that when the same amount of electricity is passed through different electrolytes/elements connected in series, the mass of substance liberated/deposited at the electrodes is directly proportional to their equivalent weights. 
When amount of substance enters into a derived quantity, it is usually as the denominator: such quantities are known as molar quantities.
For example, the quantity which describes the volume occupied by a given amount of substance is called the molar volume, while the quantity which describes the mass of a given amount of substance is the molar mass.
Molar quantities are sometimes denoted by a subscript Latin "m" in the symbol, e.g.
"C""p",m, molar heat capacity at constant pressure: the subscript may be omitted if there is no risk of ambiguity, as is often the case in pure chemistry.
The main derived quantity in which amount of substance enters into the numerator is amount of substance concentration, "c".
This name is often abbreviated to "amount concentration", except in clinical chemistry where "substance concentration" is the preferred term (to avoid any possible ambiguity with mass concentration).
The name "molar concentration" is incorrect, if commonly used. 
Faraday's laws of electrolysis.
First law of electrolysis.
In 1832, Michael Faraday reported that the quantity of elements separated by passing an electric current through a molten or dissolved salt is proportional to the quantity of electric charge passed through the circuit.
This became the basis of the first law of electrolysis: formula_1