=Compressed Guncotton.=--Clippings and other waste from cotton-mills are thoroughly purified from oil and fatty matters by treatment with alkali and extraneous substances removed. The material is then opened up by a carding-machine and cut into suitable lengths. After thorough drying and when quite cold small quantities at a time are immersed in a cool mixture of 1 nitric acid (s. g. 1.52) and 3 sulphuric acid (s. g. 1.85). The excess of acid is then removed and the cotton carefully washed, reduced to pulp, purified, and compressed into given weights and shapes by a powerful hydraulic press, and weighs 60 lbs. per cubic foot. The disks or slabs can be cut into smaller sizes with a sharp saw or knife without danger, care being taken to press them between boards while so doing to prevent their falling to pieces. It has from 2 to 2½ times the strength of gunpowder for equal weights when the charges are well tamped, and 4 times the strength of gunpowder when the charges are untamped; it ignites at a lower temperature than gunpowder, as it may explode at 277° F. and must explode at 400° F.; it is comparatively insensible to shocks--caissons containing dry guncotton have been frequently inflamed by the penetration of a bullet from a military rifle, but never exploded,[11] while wet guncotton in a condition for service cannot possibly be ignited by the same means even at the shortest ranges. Wet guncotton is not easily ignited, burns up quietly in the open air, is not sensitive to friction; but if fired by a strongly charged percussion-cap it will explode with great violence. It does not deteriorate when wet and is then perfectly safe to handle. It is therefore stored in a wet state (as it cannot be exploded except by the detonation of other disks of dry guncotton); but it should not be exposed to a temperature that will freeze the water in the cakes, if possible. While frost has no effect on dry guncotton, it causes a mechanical disintegration of the wet compressed variety. In the field the slabs are carried _wet_; the disks _dry_ and packed in hermetically sealed tins. These disks are used as primers, and have attached to them, when used, a fulminate fuze. =To Fire Guncotton=, the fuze is cut to the required length and inserted in the hollow end of the detonator, especial care being taken to push it down so as to rest on the quick-match; the tube is then slightly bent to prevent the fuze from being withdrawn. The small end of the detonator is then gently inserted into the primer (the dry disk) so as to fill the entire length of the hole in the latter. If it is loose, a piece of paper or grass must be wrapped round to make it fit tight. The primer must be placed in close contact with the charge to be fired. Care must be taken that no sparks from the fuze can fall on the charge, which might then burn instead of exploding. Bear in mind that a moist primer is certain to cause failure.