Cotton Gin: Ajanta Roller Gins, Whitney's Wire Hooks and Munger's Air Pipes

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The earliest evidence of a cotton gin comes from fifth-century India in Buddhist paintings in the Ajanta Caves, a single roller pressed against a flat stone. Dual roller gins appeared in India and China between the 12th and 14th centuries, and under the Delhi Sultanate and early Mughals the worm gear and crank handle let one man and a boy clean 250 pounds a day. That churka gin reached the American South in the mid-1700s but only worked on long staple cotton from coastal areas such as the Sea Islands. Inland short staple cotton had sticky green seeds, and cleaning one pound by hand took 10 hours. In 1793 Eli Whitney built a cylinder of wire hooks that pulled fiber through ginning ribs, with a brush cylinder clearing the lint.

Whitney patented the gin in 1794 but lost years to patent fights while planters copied it, and Hodgen Holmes patented the saw gin. With the gin, two or three enslaved workers could clean 50 pounds a day, moving the bottleneck into the fields. Production rose from 750,000 bales in 1830 to 2.85 million in 1850, and the enslaved population grew from about 700,000 in 1790 to around 3.2 million in 1850, an expansion historians tie to the Civil War. Fones McCarthy patented a knife roller gin in 1840. In 1879 Robert S. Munger in Texas, working with his wife, built the system ginning outfit, moving cotton through pneumatic pipes, which ended small plantation gins. Modern gins handle up to 15 metric tons an hour.

• An 1883 pamphlet, Woman as Inventor, credits Catherine Littlefield Greene with suggesting the brush.
• By the time patent law let Whitney enforce his claim, his patent had one year left.
• The cotton boom built up ports at New Orleans, Mobile, Charleston and Galveston and northern machine shops.
• Modern modules weigh up to 10 metric tons and are torn apart by spiked rollers before entering a 16-inch suction pipe.
• Stick machines use centrifugal force to fling out debris, and researchers are trying to turn gin waste into ethanol.