The history of the regulation of the working day in certain branches of production, and the struggle still going on in others in regard to this regulation, prove conclusively that the isolated labourer, the labourer as "free" vendor of his labour power, when capitalist production has once attained a certain stage, succumbs without any power of resistance. The creation of a normal working day is, therefore, the product of a protracted civil war, more or less dissembled, between the capitalist class and the working class.
Marx, Capital, Volume 1, Marx Engels Collected Works Volume 35 (International Publishers), p.303
The contract by which he sold to the capitalist his labour power proved, so to say, in black and white that he disposed of himself freely. The bargain concluded, it is discovered that he was no "free agent", that the time for which he is free to sell his labour power is the time for which he is forced to sell it, that in fact the vampire will not lose its hold on him "so long as there is a muscle, a nerve, a drop of blood to be exploited". For "protection" against "the serpent of their agonies", the labourers must put their heads together, and, as a class, compel the passing of a law, an all-powerful social barrier that shall prevent the very workers from selling, by voluntary contract with capital, themselves and their families into slavery and death. In place of the pompous catalogue of the "inalienable rights of man" 26° comes the modest Magna Charta of a legally limited working day, which shall make clear "when the time which the worker sells is ended, and when his own begins".
Marx, Capital, Volume 1, Marx Engels Collected Works Volume 35 (International Publishers), p.306-307
We see then, that, apart from extremely elastic bounds, the nature of the exchange of commodities itself imposes no limit to the working day, no limit to surplus labour. The capitalist maintains his rights as a purchaser when he tries to make the working day as long as possible, and to make, whenever possible, two working days out of one. On the other hand, the peculiar nature of the commodity sold implies a limit to its consumption by the purchaser, and the labourer maintains his right as seller when he wishes to reduce the working day to one of definite normal duration. There is here, therefore, an antinomy, right against right, both equally bearing the seal of the law of exchanges. Between equal rights force decides. Hence is it that in the history of capitalist production, the determination of what is a working day, presents itself as the result of a struggle, a struggle between collective capital, i. e., the class of capitalists, and collective labour, i. e., the working class.
Marx, Capital, Volume 1, Marx Engels Collected Works Volume 35 (International Publishers), p.243
Capital that has such good reasons for denying the sufferings of the legions of workers that surround it, is in practice moved as much and as little by the sight of the coming degradation
and final depopulation of the human race, as by the probable fall of the earth into the sun. In every stock-jobbing swindle every one knows that some time or other the crash must come, but every one hopes that it may fall on the head of his neighbour, after he himself has caught the shower of gold and placed it in safety. *Après moi le deluge!* is the watchword of every capitalist and of every capitalist nation. Hence Capital is reckless of the health or length of life of the labourer, unless under compulsion from society. To the outcry as to the physical and mental degradation, the premature death, the torture of overwork, it answers: Ought these to trouble us since they increase our profits? But looking at things as a whole, all this does not,
indeed, depend on the good or ill will of the individual capitalist. Free competition brings out the inherent laws of capitalist production, in the shape of external coercive laws having power over every individual capitalist.
Marx, Capital, Volume 1, Marx Engels Collected Works Volume 35 (International Publishers), p.275-276
Constant capital, the means of production, considered from the standpoint of the creation of surplus value, only exist to absorb labour, and with every drop of labour a proportional quantity of surplus labour. While they fail to do this, their mere existence causes a relative loss to the capitalist, for they represent during the time they lie fallow, a useless advance of capital. And this loss becomes positive and absolute as soon as the intermission of their employment necessitates additional outlay at the recommencement of work. The prolongation of the working day beyond the limits of the natural day, into the night, only acts as a palliative. It quenches only in a slight degree the vampire thirst for the living blood of labour. To appropriate labour during all the 24 hours of the day is, therefore, the inherent tendency of capitalist production. But as it is physically impossible to exploit the same individual labour power constantly during the night as well as the day, to overcome this physical hindrance, an alternation becomes necessary between the workpeople whose powers are exhausted by day, and those who are used up by night. This alternation may be effected in various ways; e.g., it may be so arranged that part of the workers are one week employed on day work, the next week on night work.
Marx, Capital, Volume 1, Marx Engels Collected Works Volume 35 (International Publishers), p.263-264