Extending workday

So how does the amount spent on wages remain constant with the workday being extended? Would this not just appear as additional labour performed for free or a reduction in wages?

For example if an 8-hour workday consisting of 4 hours necessary and 4 hours surplus labour,

80c + 5v + 5s

is extended to a 12-hour workday, now with 4 additional surplus-labour hours (production of absolute surplus-value),

80c + 5v + 10s

how does the amount spent on wages remain constant here? I'm guessing this might be answered somewhere in vol. 1. The relevant passage is this:

The increase of absolute surplus-value, or the prolongation of surplus-labour, and thus of the working-day, while the variable capital remains the same and thus employs the same number of labourers at the same nominal wages [...]

I suppose if wages aren't

I suppose if wages aren't based on hours worked (maybe something like $5 for every week of work; not sure how remuneration of workers in 19th century England was done) then an extension of the workday could occur, with the same expenditure on wages, without it appearing to workers they are performing additional labour for free.

Edit, so yes, it's in chapter 20 of vol. 1. Cleaver explains it well here I think:

Cleaver

So, if the daily wage is fixed, e.g., 3s, then if the capitalists impose longer hours, the effective hourly wage drops:
With a daily wage of 3s, 10 hours of work implies hourly wage of 3s/10 = 36d/10 = 3.6d = 3 6/10d = 3 3/5d.
Or, w/12 hrs of work, the hourly wage falls to 3/12 = 3d
Or, w/15 hrs of work, the hourly wage falls to 3/15 = 2 2/5d
As we saw in chapter 10, if the working day is lengthened with no change in the value of labor power, then the capitalists make more surplus value or profit.

...

Cleaver

We might note, for example, how salaries - which are paid at a fixed rate, usually so-and-so-much per year (and thus per month) leave open the amount of actual labor time required. We might also note how this means that jobs that pay salaries generally designate the tasks to be performed and that those tasks often require far more than the standard number of hours per week, e.g., 40 hrs in the US after WWII. Thus the commonplace that salaried workers wind up spending many extra hours in their offices and also take home briefcases full of work to be done in their supposed "free time."

etc.

I see, that clears it all up!

woa, Very detailed

woa, Very detailed calculation