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52 INTERNATIONAL EXHIBITION, 1876. success to the perfection of late attained in the manufacture of this ammunition. EXPLOSIVE AND FULMINATING COMPOUNDS. During the past century a great advance has been made in knowl edge respecting the nature of explosive agents, and many new varie ties have been added to the list available for use in peace and in war. Indeed, one hundred years ago gunpowder was exclusively employed, while to-day it is often superseded by more powerful and economical agents then quite unknown. Although, from obvious reasons, this class could only be represented by imitations at the Centennial Exhibition, the subject is one of so much importance that a few'words respecting the explosives now in common use will not be out of place. The effects of an explosion are due to the sudden evolution of a great volume of highly-heated gas in a confined space. Detonation implies that this physical change occurs instantaneously, giving rise to a violent blow rather than to a sustained pressure. The essential constituents of most explosives are carbon, oxygen, and nitrogen ; and the gaseous products consist mainly of carbonic acid gas and free nitrogen, but other elements are often present and enter into the chemical reactions. Modern explosive agents may be divided into two great classes, mechanical mixtures and chemical compounds. To the former be long the nitrates and chlorates, and to the latter gun-cotton, nitro glycerine and its compounds, the picrates, and the various fulminates, each of which will be briefly considered in turn. The Nitrates.—Gunpowder is the best-known type of this class. It is a mechanical mixture of potassium nitrate, carbon, and sulphur, the proportions by the atomic theory being about 74.5, 13.5, and 12.0 respectively. For the military service the proportions usually differ but slightly from these figures; for sporting purposes the potassium nitrate is often increased, and for blasting purposes decreased. The general characteristics of gunpowder and the usual process of manu facture are too well known to require notice here; but a very recent modification in the latter, invented and introduced in Russia by Colonel Wierner three years ago, merits attention,—especially as sam ples of the powder thus made have been submitted to the Judges of Group XVI. The new process consists, essentially, in replacing the wetting, compressing, and drying processes by dry hot pressure between steam-heated plates. The temperature should be about 248 Fah. A pressure of 30 atmospheres gives a density from 1.66 to 1.70, and of