out the nitrate groups by treatment with ammonium or calcium sulfide.
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. Aeroplane wings can be made of
cellulose acetate sheets as transparent as those of a dragon-fly and not
easy to see against the sky.

The nitrates, sulfates and acetates are the salts or esters of the
respective acids, but recently true ethers or oxides of cellulose have
been prepared that may prove still better since they contain no acid
radicle and are neutral and stable.

These are in brief the chief processes for making what is commonly but
quite improperly called "artificial silk." They are not the same
substance as silkworm silk and ought not to be--though they sometimes