GENERAL REPORT OF THE JUDGES OF GROUP XVI. 130 atmospheres from 1.86 to 1.90. The powder should remain under pressure for ten minutes. It is claimed that by this change the needful machinery and the cost of production are largely reduced; that the powder is rendered less absorbent; that the operation is less dangerous, because from the great saving of time less bulk is operated upon at once; and, lastly, that greater uniformity in density is secured. After soaking samples of the powder shown at this Exhibition for ten days in pure water the plates did not break up, while powder of ex cellent quality made in the usual way, treated in like manner, soon became thoroughly disintegrated. The process can be used as well for blasting powder made from sodium nitrate as for the higher grades made from potassium nitrate. Although gunpowder has been in general use for more than five hundred years, the modern system of experimental research has led to great advances in knowledge respecting it during the past century. The investigations of Count Rumford, communicated to the Royal Society in 1797, furnished data respecting the pressure developed by its explosion, which have continued to be regarded as the best standard until very recently (1875), when the elaborate results obtained by Captain Andrew Noble and Mr. Abel were published. In 1825, Chevreul drew attention to the difference in decomposition caused by variations in the conditions under which gunpowder may be exploded. General Piobert made many valuable experiments between the years 1831 and 1836, which were fully elaborated in his standard work pub lished in 1859- I n 1841, Colonel Rumford, U. S. A., devised a system of measuring the pressure exerted in different, parts of the bore of a cannon, which has done much to improve the construction of modern ordnance. In 1856, General Rodman, U. S. A., invented better appa ratus for observing these pressures, and by its aid discovered the im portant and normal changes which may be caused in the ratio between the pressure exerted upon the gun and the velocity communicated to the projectile by judiciously varying the size and composition of the grains. These studies *led him to invent mammoth and perforated cake powder, which have been adopted, with certain modifications, by the British Government under the names of pellet and pebble powder, and by the Russians under the name of prismatic powder. Without these inventions the immense guns now adopted in all military ser vices could never have been introduced. The general principle upon which these improvements are based is the fact that gunpowder does not detonate, but burns; and that the rate of burning may be varied by changing the size and form of the grains, and by regulating their density and hardness and the mechanical condition of their