ENGLISH GREAT GUNS.
The largest rifled cannon in the world is a 100-ton gun, made for the Italian government by Sir William Armstrong's firm. But the English government is preparing to outdo this, and already has the plans ready for a gun of 164 tons. It hesitates, in fact, between a weapon of this size and one of 200 tons, a mass of metal which its shops are now perfectly able to handle. The meaning of the term—200-ton gun—is simply this: a tube of iron and steel of that weight, fifty feet long, having a calibre of 20 inches, and firing a shot of 3,500 or 4,000 pounds weight, with a charge of 800 pounds of powder! The human capacity for astonishment has grown perforce as the successive steps have been taken from the guns of ten and twenty tons to these weapons, which must remain huge whatever further advances are made. The character of warfare with them is best indicated by the fact that the 200-ton gun must be handled entirely by machinery. The advent of these unmanageable weapons is signalized by the invention of a hydraulic apparatus for working them. The vast shock of the recoil from the bursting of thirty-two kegs of powder—enough to throw down 1,200 tons of rock in mining—is taken up by a cylinder pierced with small holes. These holes are capped with valves, held down with a pressure of fifty tons to the square inch. When the force of the recoil exceeds this the water is forced out of the holes and the recoil thus taken up in work done. The breech of the piece is supported on a hydraulic ram, the elevation of which depresses the muzzle of the gun below the level of the deck, and brings it exactly in line with an iron tube carrying the sponge. This is run up to the base of the powder chamber, a deluge of water rushes from apertures in its head, and the bore is completely cleaned out and every spark of remaining fire extinguished. The rammer then retires, the sponge is taken off, and the powder hoisted by tackle to the muzzle, whence the rammer pushes it home, and then does the same for the shot. The shot and cartridge, weighing together about 1,350 pounds, are stored on little iron carriages, every charge in the magazine having its own carriage. The loading finished, the gun is raised, pointed, the port flies open, and the discharge immediately follows. What the result of the blow from such a projectile would be is not to be imagined. It is acknowledged, however, that in the struggle for mastery the gun has beaten defensive armor. No ship has been built to stand the shock of a 3,500 pound bolt moving at the velocity of 1,300 or 1,500 feet a second.
EAR TRUMPETS FOR PILOTS.
Prof. Henry has turned his attention to the discovery of means for increasing the distinctness of sound signals at sea. It is a very large hearing trumpet, projecting mouth foremost from the top of the pilot-house of a steamboat. But he soon found that a single hearing trumpet would not answer the purpose, for though it greatly augmented the perceptive power of the ear, it destroyed the capacity of that organ for distinguishing the direction of sound. For this purpose two ears are necessary. Prof. Henry then made use of two hearing trumpets, the axes of which are separated about 30 inches. An india-rubber tube proceeding from the axis of each is placed so as to terminate in the ear of the observer—one in each ear. With this instrument the audibility of the sound was very much increased, but as a means of determining the direction of the source of sound, it was apparently of little use. For this purpose the unaided ear is sufficient, provided the head is placed above all obstructions and away from reflections.
HOT WATER IN DRESSING ORES.
We have before alluded to the investigations made to ascertain the reason why clay settles more rapidly in solutions of some salts than in pure water, a fact which appears contrary to reason, since it might be inferred that the greater the specific gravity the more buoyant the fluid. But the fact is abundantly confirmed, and it is likely to find important application some day in the arts. The property which every substance has of sinking through a fluid of less density than its own forms the basis upon which nine-tenths of the gold and copper, and probably six-tenths of the silver produced in this country, is extracted from its ores. It is the foundation of the art of ore dressing, one of the most important parts of metallurgy. Anything which increases the rapidity and thoroughness of the process may have a fortunate application in this art. Mr. Ramsay, of the Glasgow university laboratory, thinks the property in question depends upon the varying absorption of heat by the different solutions. When water containing suspended clay is heated the rapidity of settling is proportional to the heat of the water. This mode of accelerating the movement of fine sediments in water is perhaps more easily applied than the solution of caustic soda or potash, or of common salt. Rittinger, by a mathematical discussion of the principles which control the downward movement of solid particles in an ascending stream of water, showed that the separation of light from heavy minerals is more complete with solutions of density greater than that of water than in water alone. He found a solution of 1.5 sp. gr. extremely favorable. If the addition of heat will increase the effect of such a solution, it may become possible to separate, by means of the continuous jig, minerals so near in specific gravity as barite and galena. This whole subject of ore dressing is one of the most important questions connected with the future of mineral industry in America. In the Mississippi valley everything connected with metallurgy, from the fuels to the finished metal, will one day be closely dependent on it.
OCEAN ECHOES.