Similar ‘gins’ existed prior to Eli Whitney's patented cotton gin, such as the churka, which had been in use in India for centuries. However, these only functioned with other varieties of cotton, not the upland variety grown in the southern USA. The modern cotton gin consists of a roller carrying a set of circular saws. These project through a metal grill in a hopper containing the seed bolls. As the roller rotates, the saws pick up the cotton fibres, leaving the seeds behind.

The cotton gin revolutionized the cotton industry in the USA by mechanizing the most labour-intensive part of the processing, which was separating the seeds and fibres. As a consequence, slavery became further enmeshed into the economy of the south. Prior to the gin, raising cotton was only profitable for the few large plantations that could afford the necessary number of slaves to fulfil the manual labour involved. With the use of the gin, the crop became cost-effective for smaller farms. As the number of farms raising the crop grew, so did slave labour; while in 1790 there had been some 657,000 slaves, by 1810 that number had risen to 1.3 million.

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cotton gin