value of his labour-power, and produces the surplus-value, this sum constitutes the actual time during which he works, i.e., the working day.
CHAPTER X.
THE WORKING DAY.
section 1.—the limits of the working day.
We started with the supposition that labour-power is bought and sold at its value. Its value, like that of all other commodities, is determined by the working time necessary to its production. If the production of the average daily means of subsistence of the labourer takes up 6 hours, he must work, on the average, 6 hours every day, to produce his daily labour-power, or to reproduce the value received as the result of its sale. The necessary part of his working day amounts to 6 hours, and is, therefore, cæteris paribus, a given quantity. But with this, the extent of the working day itself is not yet given.
Let us assume that the line A B represents the length of the necessary working time, say 6 hours. If the labour be prolonged 1, 3, or 6 hours beyond A B, we have 3 other lines:
| Working day I. | Working day II. | Working day III. |
| A———B—C. | A———B——C. | A———B———C. |
representing 3 different working days of 7, 9, and 12 hours. The extension B C of the line A B represents the length of the surplus labour. As the working day is A B + B C or A C, it varies with the variable quantity B C. Since A B is constant, the ratio of B C to A B can always be calculated. In working day I. it is 16, in working day II, 36 in working day III, 66 of A B. Since, further the ratio surplus working timenecessary working time determines the rate of the surplus-value, the latter is given by the ratio of B C to A B. It amounts in the 3 different working days respectively to 1623, 50 and 100 per cent. On the other hand, the rate of surplus-value alone would not give us the
