Mechanical cotton

Other applications were herbicides, primarily sodium arsenate, as weed killers for railroad and telephone posts, desiccators, mainly arsenic acid (H3ASO4), for example, to facilitate mechanical cotton harvesting and for tobacco and blueberry fields. Most of these compounds, their derivatives or decomposition products are still present in various regions and contribute significantly to the arsenic burden of soils and waters. 

In a 500 ml. bolt-head flask provided with a thermometer (reaching almost to the bottom) and a calcium chloride (or cotton wool) guard tube, place 100 g. of a-bromo-wo-valerj l bromide and 50 g. of dry, finely-divided urea. Start the reaction by warming the flask on a water bath the temperature soon rises to about 80°. Maintain this temperature for about 3 horns the mass will liquefy and then resolidify. Transfer the sticky reaction product to a large beaker containing saturated sodium bicarbonate solution, stir mechanically and add more saturated sodium bicarbonate solution in small quantities until effervescence ceases. Filter at the pump, suck as dry as possible and dry the crude bromural upon filter paper in the air. RecrystaUise the dry product from toluene. Alternatively, recrystaUise the moist product from hot water (ca. 700 ml.). The yield of pure brommal, m.p. 154-155°, is 28 g. 

The mechanical properties of acryUc and modacryUc fibers are retained very well under wet conditions. This makes these fibers well suited to the stresses of textile processing. Shape retention and maintenance of original bulk in home laundering cycles are also good. Typical stress—strain curves for acryhc and modacryUc fibers are compared with wool, cotton, and the other synthetic fibers in Figure 2. 

The second most important (3%) use of sodium chlorate in 1990 was as an intermediate in the production of other chlorates and of perchlorates. The use of sodium chlorate as in agricultural appHcation amounted to about 7000 metric tons in 1990. The agricultural use of sodium chlorate is as a herbicide, as a defoHant for cotton (qv). Magnesium chlorate is used as a desiccant for soybeans to remove the leaves prior to mechanical picking (see Desiccants). 

Harvesting. Except for the cotton gin, the introduction of the mechanical harvester has probably had a greater effect on cotton production than any other single event. Commercial mechanical harvesters were introduced into the United States after World War 11. By 1955, about 23% of the cotton was mechanically harvested. That value had increased to 85% by 1965. In the early 1990s more than 99% of the U.S. cotton crop was mechanically harvested, although cotton was stiH hand harvested in some other countries. 

Once the plant is ready, the cotton is mechanically harvested with either a spindle picker or cotton stripper. The spindle picker selectively harvests seed cotton from open boUs. The unopened boUs are left on the plant and can be picked at a later date. The spindle picker uses a rotating tapered barbed spindle to remove the cotton from the bur (seed case). The seed cotton is wrapped around the spindle, pulled from the bur, removed from the spindle with a mbber doffer, and then transferred to a basket. 

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