Now rack down the body-tube by means of the coarse adjustment until within 1⁄16 of an inch of the cover-glass of the slide. Now see that the light from the lamp is fully on the cotton strands. Rack up or down, as the case may be, with the fine adjustment, and a wonderful sight meets the eye, for the cotton viewed through the microscope is altogether unlike what we should expect it to be.
Running completely across the field are a number of strands, varying in thickness, form and natural twist. What is meant by natural twist is very clearly shown in [Fig. 7].
Most people have seen india-rubber tubing or piping such as is used in the chemical laboratory or that often found attached to feeding bottles. Take about a foot of this and hold one end firmly. Abstract the air by means of the mouth, and it will be found that immediately the air is taken out the tube collapses. Now if the rubber be variable in thickness, here and there along these lines of least resistance will be found certain twists, and it is the same kind of twists which can be so distinctly seen as the cotton fibre is viewed through the microscope. They are exceedingly irregular in number, on equal lengths of the same single fibre. When they run for some length, and are fairly regular, the edges appear like wavy lines or corrugations. It will now be seen by the reader why these twists are so invaluable in spinning: locking and intertwining with each other, they materially assist the spinner in building up a long and continuous thread.
Fig. 7.—Transverse and longitudinal sections of cotton fibre.
Then, too, are to be seen lying close to the regularly twisted fibres a number of others which are very like ribbons, with here and there an apology for a twist, and further, a careful scrutiny will be rewarded by finding in what is reputedly the best cotton a number of filaments which do not display any twists whatever and are very much like the round tubing referred to a little while ago. Others again are quite flat, without any distinguishing twists whatever. These are said to be the half-ripe and unripe fibres, and give much trouble later on (if worked up with good cotton) to the dyer and spinner.
As the slide containing the cotton is moved laterally, it will be seen that this twisting of the fibre is continued for almost the whole length, and as many as 300 twists have been counted on a single filament. In some, the fibre tapers slightly, becoming more and more cylindrical as the end most remote from the seed is approached, until it is quite solid. These stiff ends soon disappear after the cotton has been treated in the early processes of manufacture. Thus there may be found in almost every sample of cotton what are called ripe, half-ripe and unripe cotton. The last-named kind result from—
1. Gathering the crop before the boll is properly ripened and matured.
2. Bad seasons; too much moisture and too little heat.