A-A-2522A
4.7.1 Absorption. The lot shall be expressed in terms of quantity of rags in the lot, based on 200 rags per bale. The inspection level shall be S-3, AQL 6.5 percent defective. The sample unit shall be one rag. Each sample rag shall be supported so that the are being tested does not contact any surface. One drop of distilled water and one drop of light machine oil (ISO 32 grade lubricating oil), each 0.04 milliliter in volume and 70 + 2oF (21 + 1oC), shall be applied separately to applicable sample through a capillary tube. The drops shall fall freely onto the rag from a height of approximately 2 inches (5.1 cm). The time, from initial contact of the drop with the rag until the drop is completely absorbed by the rag, shall be measured using a stopwatch. The time shall be noted to the nearest 0.1 second failure to completely absorbed the drop in less than 15.0 seconds shall fail the sample.
4.7.2 Cotton Fiber Content. The lot size shall be expressed in terms of quantity of rags in the lot, based on 200 rags per bale. The sample unit shall be one rag. The sample rag shall be randomly selected using inspection level S-3, AQL 6.5 percent defective. Rags chosen for the absorbency test may be used. The rags shall be tested in accordance with paragraph 4.7.2.1 or 4.7.2.2 to determine the presence of cotton fiber (see 3.1).
4.7.2.1 Identification of cotton. Oils, waxes, and dirt shall be removed from the specimen by washing in one of the following: either, acetone, alcohol, or a 5-percent aqueous solution of sodium hydroxide. Dyes shall be removed using one of the following methods:
(a) By oxidation, using nitric acid, hydrogen peroxide, or chlorine water;
(b) By solution, using alcohol, acetic acid, hydrochloric acid, or pyridine; or
(c) By reduction using hydrosulphite, stannous chloride, or hydrochloric acid with metallic zinc.
After dirt, oils, waxes, and dyes have been removed, place a dozen fibers from the sample onto a slide. The fibers shall be immersed in 3 or 4 drops of Herzberg’s stain, covered with a slide (avoiding air bubbles), and allowed to stand 2 minutes with surplus stain drained off. Examine the prepared fibers with a microscope using transmitted light and 100 diameters magnification. Magnification up to 500 diameters may be used if a more detailed examination is necessary. The sample fibers shall be compared with a reference sample which has been treated in the same manner.
The color of cotton (Gossypium species) in the natural state, ranges from white to ecru. The staple length of commercial cottons varies from about 1.24 inch (3.1 cm) to slightly more than 2 inches (5.08 cm). Microscopically, most fibers appear much like a twisted ribbon with rounded edges. They have no longitudinal or cross markings; the lumens vary from very narrow to over 2/3 of the diameter of the fiber. Diameters of the fibers vary from about 9 to 25 microns and average from 16-20 microns. Undyed cotton fibers are stained pink to dark red in color by Herzberg’s stain.
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