This gin, in its original and simplest form, consists of a leather roller and two steel blades. One of the latter is pressed tightly against the revolving leather roller. The fibre is drawn in by the rough surface of the roller, and, as the latter revolves, the lint is stripped from the seed, which falls into a receptacle beneath. To assist in the detachment of the seed from the fibre, the second blade is adjusted a little in front of the fixed one, and has imparted to it a rapid vibratory motion, by means of which the seed is struck from the fibre. From this action the vibrating blade has been termed the "beater," the fixed one being called the "doctor." The machine is provided with a grid, upon which the seed cotton is placed, the bars being so arranged that the seed cannot pass through them, until it has been stripped of all fibre. There are many varieties of the Macarthy gin, all constructed upon this principle, but differing in detail.
In construction, the double-action knife-roller gin, made by Dobson and Barlow, differs more widely from the original Macarthy than most others made on that principle. It has been subjected to severe test trials with other gine, at the competitions instituted by the Government of India at Manchester and Broach. The results of these trials have recently been issued, and an examination of them will show that this gin emerged from the tests with great credit to its makers.
Figs. 657,658,659 show it in front and end elevations, and in section. The roller a is solid, and composed of discs of walrus leather, compactly pressed together npon a square shaft. The knife roller b is made up of a number of discs, fitted obliquely upou a wrought-iron shaft, as seen in Fig. 657. Objection has boon taken to this form of the disc that it was liable to work all the cotton to ono side of the gin. In order to provide against this, an alternative form of the knife-roller has been constructed, which is shown in Fig. 661. The box or hopper c is for the reception of the seed cotton ; the knife d extends across the frame, and its functions are those of a "doctor"; two set screws e, one at each end of the rollers, are for the purpose of adjusting the distances between them.
The knife d is carried by the springs f, capable of adjustment by thumbscrews attached. The gin has a fast and loose driving-pulley for each roller, shown at g end m ; these being of different diameters, indicate different speeds of their respective rollers. A semicircular grid half encloses the knife-roller b, as can be seen in the section. This grid, according to choice, may be perforated with holes as at A, or have transverse or longitudinal bars as in B C (Fig. 660).
The process is as follows :—The seed cotton, being placed in the hopper c, descends upon the knife, and fills in the interstices k between the blades. By the revolution of the rollers it is brought into contact with the surface of a, which lays hold of the fibre, drawing it down. The doctor-knife d prevents
the seed being drawn along with the fibre, and the revolution of the roller b, carrying oblique blades, causes the latter to disengage the seed from tho fibre, which then drops through the grid into a receptacle beneath. The bare of the grid are so arranged that no seed to which fibre adheres can pass through, but is carried round by the roller, and again subjected to the action of the strippieg-roller, until quite cleared. The cleaned cotton is discharged upon the floor, or it may be formed into a rough sort of " lap." The disc-roller revolves at the rate of about 350 rev. a minute. A 40" gin on this principle is capable of cleaning 300-800 lb. of seed cotton in an hour, according to the description. The yield of clean cotton is 75-150 lb. At higher speeds this is increased proportionately.
The " lint " or " wool,' when thoroughly cleansed, is packed in bales by hydraulic pressure, for export. The bales are covered with coarse jute or cotton canvas, bound with ropes or iron bands. The seed yields a valuable oil (see Oils—Cotton-seed), and is made into cakes for feeding cattle.
Characters and Uses of the 1Vbre.—Seen longitudinally, the fibres of cotton appear quite inde pendent of each other ; they are flat, and always more or less twisted, like a cork-screw, as shown in Fig. 662. This last feature is quite characteristic. The length of the fibres varies from 1 to in. for long-stapled, and from 4 to in. for short-stapled. The parts indicated in Fig. 662, are —a, sections; b, longitudinal views ; 0, ends ; mag. 300. The manufacturing capacity of the fibre is discussed at length in the article on Cotton Manufactures (pp. 730-733). Its uses are further described under Hosiery, Lace, and Small Wares.
Imports and Values.—From the 14th to the 16th centuries, the cottons of Candle, Lemnos, Cyprus, Malta, Sicily, S. Italy, and the district between Jerusalem and Damascus, were those chiefly imported into Europe by the Genoese and Venetian merchants. Our imports of raw cotton in 1870 were contributed (in cwts.), as follows :—United States, 6,495,045 ; British India, 3,040,550 ; Egypt, 1,283,037 ; Brazil, 573,331; France, 330,653 ; Anatolia (Asia Minor), 51,581 ; Chili, 36,119 ; sundry European countries, 35,271 ; New Granada, 34,295 ; European Turkey, 33,278 ; Peru, 21,216; British W. Indies, 18,851; Foreign W. Indies, 14,660; W. Coast Africa, 12,503; Ceylon, 8269 ; Venezuela, 8268 ; Queensland, 8201; New South Wales, 7928 ; Syria and Palestine, 7326 ; Natal, 4368 ; Nova Scotia, 4317 ; New Zealand, 3348 ; Gold Coast, 2721; French India, 2348; Illyria and Dalmatia, 2114; British Guiana, 1812; Argentine Confederation, 1478; Euphrates and Persian Gulf, 1060 ; Malta, 832 ; Italy, 611; Greece, 571 ; Cape of Good Hope, 561; Persia, 527 ; Sierra Leone, 493 ; Siam, 135 ; Gambia, 120 ; China, 94 ; Ecuador, 28 ; Algeria, 20 ; Mexico, 18 ; Mauritius, 6.