of their length, so that the powder will yield uniformly to the pressure of the gases generated in the gun during the combustion of the charge. The ribbon or sheet is next cut into pieces of a width and length corresponding to the chamber of the gun for which it is intended, the general rule being that the thickness of the grain (when perfectly dry) shall be fifteen one-thousandths (.015) of the calibre of the gun, and the length equal to the length to fit the powder chamber. Thus, in case of the 6-inch rapid-fire gun the thickness of the grain (or sheet) is 0.09 of an inch and the length 32 inches. The sheets are next thoroughly dried, first between sheets of porous blotting-paper under moderate pressure and at a temperature between 15 deg. C. and 21.5 deg. C. for three days, and then exposed to free circulation of the air at about 21.5 deg. C. for seven days, and finally subjected for a week or longer to a temperature not exceeding 38 deg. C. until they cease to lose weight. [Footnote A: Lieut. W. Walke, "Lectures on Explosives," p. 330.] The sheets, when thoroughly dried, are of a uniform yellowish-grey colour, and of the characteristic colloidal consistency; they possess a perfectly smooth surface, and are free from internal blisters or cracks. The temperature of ignition of the finished powder should not be below 172 deg. C., and when subjected to the heat or stability test, it is required to resist exposure to a temperature of 71 deg. C. for thirty minutes without causing discoloration of the test paper.