Marx starts with a capital of £500 and gives it a shape: £410 laid out on means of production, which he calls constant, and £90 on labour-power, which he calls variable. When the work is done the product is worth £590, so the surplus-value is £90. But the new value made in the process is only £180, the £90 of wages plus the £90 of surplus, because the £410 only reappears in the product. So Marx sets constant capital to zero, as people do every day when they work out England's profit from cotton and first take off what was paid to the United States, India and Egypt for the raw cotton. What is left is the part that changes, and he measures surplus-value against that part alone. £90 over £90 is 100 per cent. He calls this the rate of surplus-value.
The rate tells you how a working day is split. Part of the day, say six hours, the worker produces only the value of his own wage. Marx calls this necessary labour. The rest is surplus-labour. The worker still labours, but he creates no value for himself, only surplus-value, which for the capitalist has all the charms of a creation out of nothing. Surplus-value is simply that extra time set solid. So the rate of surplus-value equals surplus-labour divided by necessary labour, and it is the exact degree of exploitation. The usual way of reckoning compares the £90 with the whole £500 and gets 18 per cent, a figure that would give Mr. Carey and the other harmonisers a pleasant surprise. The real rate is more than five times that. In the example the worker spends one half of the day for himself and the other half for the capitalist. Marx tests the method on a Manchester mill with 10,000 spindles in April 1871. Cotton, wear, rent and coal come to £378 a week, wages to £52, and the yarn is sold for £510. The surplus is £80, a rate of about 153 per cent, which in a ten-hour day is under four hours of necessary labour and over six of surplus. An acre of wheat in 1815 gives a rate above 100 per cent, with the surplus shared out as profit, interest, rent and tithes.
Next he takes the twelve-hour day that makes 20 lbs of yarn worth 30 shillings, and cuts the product itself into proportions. Twenty-four shillings is old value, so 16 lbs of the yarn are cotton and spindle in disguise. Only 4 lbs hold the new value of six shillings. Of those, 2 lbs replace the wage and 2 lbs are the owner's surplus. Marx then runs the same sum through time instead of space. On the manufacturer's clock the spinner earns back the cotton in the first eight hours, the tools in the next hour and thirty-six minutes and his wage in the next hour and twelve minutes, and makes the surplus in the last hour and twelve minutes. The English manufacturer uses this reckoning daily. But it breeds what Marx calls barbarian notions in anyone who wants to misunderstand it, because it makes the spinner appear to produce his own cotton, spindles, engine and coal while he spins, and to turn one working day into five.
