The down of the cotton tree or plant, of which naturalists recognise ten varieties. Some of these are to be met with in the warmer parts of Europe; but its cultivation to any extent is chiefly confined to climates within the tropics. The generality of the West India species, are annuals, whilst those of Asia are perennial both in branch and root, and rise in a straight line about eight feet high. The cotton down is contained within pods, which, when arrived at maturity, open. The down envelopes a husk called the gin, which contains the seeds of the plant; and the first operation in rendering cotton fit for manufacturing purposes, consists in freeing the down from these seeds. This is effected by first drying it in the sun until the seeds become quite hard; and then operating upon it by a machine called a gin, of which there are two kinds, the one called a roller gin and the other a saw gin. The roller gin is represented in Fig. 1. It consists of two small fluted rollers a b, about 1 inch in diameter, and 9 inches long, and generally made of hard wood; they are put in motion by the treadle c acting upon cranks or pins in the face of the fly-wheel d.
The labourer who drives the machine places the cotton on a feeding board, and the cotton is drawn in between the rollers, which being set too close to allow the seeds to pass between them, the cotton falls down the inclined board e, and the seeds drop into the box f. The saw gin is given in Fig. 2. a is a roller having a number of circular saws b fixed upon it, with a washer of wood between each; c is a grating; through which a portion of the teeth of the saws project; d is a circular brush driven by the wheel e on the axis of a, which works into a pinion on the axis of d. The cotton being put into the hopper f, the teeth of the saws lay hold of the wool and tear it through the grating, whilst the seeds are by that means separated, and roll down the inclined plane of the grating, and finally escape at the spout g; the cylindrical brush serves to clear the cotton from the teeth of the saws, and throw it clear of the cylinder, in which state it is ready to be packed for the market.