A prodigious force often arises from chemical affinity. Of this, gunpowder presents a familiar instance. It is formed of nitre, sulphur, and charcoal, which, in the ordinary state, are only combined mechanically; but no sooner is this compound ignited, than these substances are brought, by chemical action, into such close contact, as to evolve a mighty and destructive power. It seemed likely to be thrown into the shade by the discovery of gun-cotton as an explosive agent, which excited extraordinary interest throughout Europe. On projectile experiments being made, a gun, charged with thirty grains of prepared cotton, propelled an equal charge of shot, with greater force and precision, at a distance of forty yards, than were gained by the same gun loaded with a hundred-and-twenty grains of gunpowder. A rifle, charged with fifty-four and-a-half grains of gunpowder, sent a ball through seven boards, half-an-inch in thickness, at a distance of forty yards; the same rifle, charged with forty grains of gun-cotton, caused the ball to enter the eighth board. Another rifle, which had been used for elephant-shooting, and consequently carried a much larger ball, charged with forty grains of gun-cotton, forced the ball through eight boards, at a distance of ninety yards. In no case was the discharge accompanied by a greater recoil than usual; and the reports were not louder than those accompanying the discharge of guns and rifles loaded with gunpowder. According to the specification of the patentee, M. Schönbein, cotton is preferred for this purpose, freed from extraneous matters; and it is considered desirable to operate on the clean fibres of the cotton in a dry state, by means of nitric and sulphuric acids. These are mixed together in the proportion of one measure of nitric acid to three measures of sulphuric acid, in any suitable or convenient vessel not liable to be affected by the acids. A great degree of heat being generated by the mixture, it is left to cool until its temperature falls to sixty or fifty degrees Fahrenheit. The cotton is then immersed in it; and, in order that it may become thoroughly saturated with the acids, it is stirred with a rod of glass, or other material, not affected by the acids. The cotton should be introduced in as open a state as practicable. The acids are then poured or drawn off, and the cotton gently pressed by a presser of glazed earthenware, to take out the acids, after which it is covered up in the vessel, and allowed to stand for about an hour. It is subsequently washed in a continuous flow of water, until the presence of the acids is not indicated by the ordinary test of litmus paper. To remove any uncombined portions of the acids which may remain after the cleansing process, the patentee dips the cotton in a weak solution of carbonate of potash, composed of one ounce of carbonate of potash to one gallon of water, and partially dries it by pressing, as before. The cotton is