ry he cut his finger, as chemists are apt to do, and, again as
chemists are apt to do, he dissolved some guncotton in ether-alcohol and
swabbed it on the wound. At this point, however, his conduct diverges
from the ordinary, for instead of standing idle, impatiently waving his
hand in the air to dry the film as most people, including chemists, are
apt to do, he put his mind on it and it occurred to him that this sticky
stuff, slowly hardening to an elastic mass, might be just the thing he
was hunting as an absorbent and solidifier of nitroglycerin. So instead
of throwing away the extra collodion that he had made he mixed it with
nitroglycerin and found that it set to a jelly. The "blasting gelatin"
thus discovered proved to be so insensitive to shock that it could be
safely transported or fired from a cannon. This was the first of the
high explosives that have been the chief factor in modern warfare.

But on the whole, collodion has healed more wounds than it has caused
besides being of infinite service to mankind otherwise. It has made
modern photography possible, for the film we use in the camera and
moving picture projector consists of a gelatin coating on a pyroxylin
backing. If collodion is forced through fine glass tubes instead of
through a slit, it comes out a thread instead of a film. If the
collodion jet is run into a vat of cold water the ether and alcohol
dissolve; if it is run into a chamber of warm air they evaporate. The
thread of nitrated cellulose may be rendered less inflammable by taking
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