In the early 1790s, cotton growers in the United States - especially inland in the southern states - had a very large problem: their farming efforts weren't profitable. While cotton is one of the most common materials used in the creation of a large number of goods, cotton grows with the seeds enmeshed in the cotton. To make matters worse, the only type of cotton that could be grown inland in the United States was a type of cotton with sticky green seeds that were difficult to remove from the cotton ball. The difficulty meant that many hours of labor would be needed to remove the seeds from each cotton ball as the crop was harvested.
Eli Whitney, being in need of money to pay some debts and abounding with creative insight, had only recently arrived in the Southern United States in 1792 where he learned of the problem. After several months of work, he designed the first machine that could efficiently remove seeds from cotton at the astounding rate of one and one-half tons of cotton each day. He called his design the cotton gin.
One of the most ingenious parts of his invention is its simplicity. The first cotton gin looked very much like a desk-top laser printer except that it had a crank on the side. It was box-shaped and not particularly big (although larger models would follow that would take a horse or a water mill to crank). Like a typical laser printer, the cotton gin had a hole in the top with a sloped surface through which cotton would be fed into the machine. A hand crank extended from one side of the gin.
The machine worked by feeding the raw cotton complete with seeds into the interior of the machine through the slot on the machine top (the place where the paper would exit in many laser printers). The cotton would feed against a cylinder covered with spikes which revolved as the crank would be turned on the outside of the machine. The spikes on the rotating cylinders would seize the cotton fibers and pull the cotton upward into small slotted openings above the cylinder. The slots were too small for the seeds to pass through, and the seeds would be forced out of the cotton as the cotton fibers continued through the slots. The separated seeds would fall away from the fibers into a small compartment in the front of the gin.
The fibers or lint that carried through the slots would continue to hang onto the spikes as they rotated downward into the rear portion of the machine. This lint would then encounter a brush that was fixed to a second rotating cylinder located towards the rear of the cotton gin which brushed upward against the lint that was rotating on the downward portion of its motion. The brushes on the rear cylinder would brush the cotton off the spikes into a compartment in the rear of the gin. The spikes would then continue rotating to the front of the machine where it would meet more cotton and the entire process would begin again.
The cotton gin led to a revolution in the cotton industry. With its invention, cotton could be grown profitably even in the inner regions of the Southern States. It seemed inevitable that Eli's invention would make him very wealthy, except that Eli Whitney and his partner, Phineas Miller, got greedy and asked too much in payment for the use of the gin. Farmers, already strapped for cash, began making knock-offs of the invention claiming that their minor adaptations were enough to make it a unique product that differed in material respects from the Whitney's patented cotton gin. Ironically, one of the most important inventions in American history which led to the creation of a profitable cotton industry in the South ended up making the inventor no profit.
"The Cotton Gin", http://www.eliwhitney.org/cotton.htm
"The Cotton Gin and Eli Whitney", http://inventors.about.com/od/cstartinventions/a/cotton_gin.htm
"Cotton Gin", http://www.bookrags.com/research/cotton-gin-woi/