Many experiments have been made by observing the velocity of transmission of inflammation of trains of powder under various circumstances, but they do not show us what would be the velocity in a confined charge. The velocity increased with the section of the train, and further when at the end first lighted, there was an obstruction to the escape of gas, as in the case of a gun, a much shorter time was required for complete inflammation. ~Time of decomposition depends upon form of grain.~ When the charge of powder in a gun is ignited the grains being enveloped by the heated gas, we may consider that each grain is ignited over its whole surface at once. If the grains of powder were of equal or regular form, the time each would be consuming, might be easily calculated, but since in ordinary cases they are irregular in form, although the grains may be of the same weight, the time necessary for their complete decomposition will be very different. ~Circumstances affecting combustion.~ The quickness of combustion will depend upon the dryness of the powder, the density of the composition, the proportion of the ingredients, the mode of manufacture, and the quality of the ingredients. ~Combustion of cubical grains considered.~ Were a cubical grain to be ignited upon its whole surface, the decomposition may be supposed to take place gradually from the surface to the centre, and the original cubical form to remain until the whole is consumed, the cube becoming smaller and smaller. If, then, the rate of burning be the same throughout, the quantity of gas generated in the first half portion of the time will evidently be considerably more than in the latter half, as in the latter case there will be a much lesser surface under the influence of flame. ~Elongated and cylindrical grains.~ If the form of the grain be elongated, then will the quantity of gas generated in a given time from a grain of similar weight to that of the cube or sphere, be increased, on account of the greater ignited surface, and consequently the time necessary for its combustion will be diminished. If it be of a cylindrical form for example, this time must be reckoned from the diameter of the cylinder, its length not influencing it in the least, although as we have seen, it enters into the consideration of the quantity of the gas generated in a given time. ~Large grain.~ In the ordinary large-grain powder, the majority of the grains are of the elongated or flat form, from whence considerable advantage is derived, particularly in short guns, since it causes the greatest portion of the charge to be decomposed before the projectile is moved sensibly from its original position. ~Mealed powder.~ If the charge be composed of mealed powder a longer time is found to be necessary for the complete combustion of the whole than in the case where the substance is granulated, and the initial velocity of a shot is reduced about one third by employing the substance in that state.