This restores the original cellulose, but now it is an endless thread of
any desired thickness, whereas the native fiber was in size and length
adapted to the needs of the cottonseed instead of the needs of man. The
old motto, "If you want a thing done the way you want it you must do it
yourself," explains why the chemist has been called in to supplement the
work of nature in catering to human wants.
Instead of nitric acid we may use strong acetic acid to dissolve the
cotton. The resulting cellulose acetates are less inflammable than the
nitrates, but they are more brittle and more expensive. Motion picture
films made from them can be used in any hall without the necessity of
imprisoning the operator in a fire-proof box where if anything happens
he can burn up all by himself without disturbing the audience. The
cellulose acetates are being used for auto goggles and gas masks as well
as for windows in leather curtains and transparent coverings for index
cards. A new use that has lately become important is the varnishing of
aeroplane wings, as it does not readily absorb water or catch fire and
makes the cloth taut and air-tight.
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