Page:Popular Science Monthly Volume 3.djvu/669

Rh vapor, viz., oxygen and hydrogen, are dissociated at 1,298° Fahr. "If, therefore," says the author, "we heat a bar of iron to fully 1,298°, and place it over a globule of water upon an anvil, a blow with a hammer will elicit the detonation of a rifle; I have repeated this experiment often. The elements of the water dissociate by the heat, and instantaneously recombine in cooling, causing the detonation."

The degree of dissociation, as of evaporation, depends on the pressure: under four atmospheres (60 lbs.), the heat required for dissociation is 1,870°. But the question arises, If the vapor dissociates at these temperatures, why do not the gases instantaneously combine and detonate? The reason is plain: in the boiler the atoms at once become mixed with a volume of steam sufficient to render them inexplosive.

The condition requisite for the generation of explosive gas in a boiler is that vapor be in contact with a surface heated to 1,298°, or higher, according to the pressure, as we have seen. Now, this condition may occur in a boiler filled with water, owing to the property which that liquid possesses of assuming the spheroidal shape when in contact with a highly-heated surface. "It is, therefore, not difficult to conclude," says the author, "that, in case of very heavy firing, a thin film of vapor may form between the water and the boiler, and, when this is once formed, the heating of the boiler would be so rapid that nothing but the cooling process of dissociation, which would then commence, could save it from completely burning through."

Explosion would then occur whenever—
 * 1) The oxyhydrogen gas, as compared with the steam, rises to the explosive proportion; or,
 * 2) When the steam, by condensation, falls to the explosive proportion. To make explosion possible, the proportion of oxyhydrogen gas to vapor must be at least as 1 to 7.

Scientific Education in England.—Sir Josiah Mason, a manufacturer of Birmingham, is about to found a scientific college in that town on a most liberal scale. It is intended to afford thorough systematic scientific instruction, specially adapted to the practical, mechanical, and artistic requirements of that great centre of manufacturing industry. Systematic instruction is to be given in mathematics; abstract and applied physics; chemistry, theoretical, practical, and applied; the natural sciences, especially geology and mineralogy, with their application to mines and metallurgy; botany and zoology, with special application to manufactures; and physiology, with special reference to the laws of health. The English, French, and German languages will be taught, but mere literary instruction is excluded. No principal, professor, teacher, or other officer of the college, is ever to be called upon to make any "declaration as to, or submit to any test whatever of, his religious opinions," and the institution is to admit all persons "without distinction of age, class, creed, race, or sex," to the popular lectures; while the regular course will be open to qualified persons of all classes, "especially the more intelligent youth of the middle class." This Nature calls "one of the most princely gifts yet made to posterity in England by one of her wealthy sons."

The Hotchkiss Revolver-Cannon.—Some trials were recently made, says the Revue d'Artillerie, at the Satory Polygon, with a revolving cannon, invented by Mr. Hotchkiss, and intended for the Italian Government. The special object of these experiments was to ascertain the mechanical value of this engine. This new arm (whose calibre is 1½ inch) differs essentially from all other mitrailleuses hitherto brought before the public, particularly in this, that it discharges a small cast-iron shell with percussion fuse, the effects of which may be formidable at distances relatively considerable.

We will, at another time, present a complete description of this gun, but for the present must content ourselves with giving some details of the ammunition employed. This consists of a cartridge with shell attached. The cartridge proper consists of a soldered tube of tin, with one end closed to form a cup. This closed end is reënforced, within and without, by two iron caps, and fastened with three rivets to a broader iron plate, which forms the true base of the cartridge, bears the pressure of the gases, and affords a grip to the extractor. The