Year after year the capitalists buy labor-power, paying for it at its value (in the case of the miner at $2.00 a day). The capitalists own the products of the workers—equalling ten hours of labor. They exchange a commodity (gold, or money), containing two hours of labor for labor-power (containing two hours of necessary labor—represented by the necessities of life). But when the miner goes home at night the capitalists find themselves owners of the coal he has dug, which contains ten hours of labor.
Coal (representing ten hours of labor) will exchange for gold (or money) containing ten hours of labor; in this case for $10.00. The miner has produced $10.00 worth of coal. He received $2.00.
The eight hours of value, or $8.00 worth of coal, which the capitalists appropriate, is surplus value, for which they give no equivalent.
"It is this sort of exchange between capital and labor upon which capitalistic production, or the wages system, is founded, and which must constantly result in reproducing the workingman as workingman and the capitalist as a capitalist.
"The rate of surplus value, all other circumstances remaining the same, will depend on the proportion between that part of the working day necessary to reproduce the value of the laboring-power and the surplus time or surplus labor performed for the capitalist. It will, therefore, depend on the ratio in which the working day is prolonged over and above that
