Page:Collier's New Encyclopedia v. 03.djvu/574

LEFT ELECTBO-METALLURGY 500 ELEPHANT it can be removed from the bath and welded on the anvil. The third process is known as the incandescent process. The two pieces of metal to be welded are connected to opposite poles of a genera- tor, and then brought together. The re- sistance offered raises the surfaces to incandescence, when they can be welded. Electro-plating depends upon the electrolysis of a solution of a metallic salt, and by its means a coating of the metal in solution is deposited upon an- other metal which forms the electrode of the cell in which the electrolysis takes place. For silver plating a solution of potassium silver cyanide is used; for nickel plating, nickel ammonium sul- phate; and for copper plating, a solu- tion of copper sulphate. In all cases the general procedure is the same. The metal to be plated forms the kathode of the cell, and must be perfectly clean and free from all traces of grease. The solution must also be kept moving, either by means of paddles or by mov- ing electrodes. The current required is small, and seldom exceeds 12 amperes per square foot, being, in the case of nickel plating, as low as four amperes per square foot. Electfic refining is a similar process to electro-plating, but in this case the impure metal forms the anode of the cell, the pure metal being first brought into solution and then deposited on the kathode. For instance, in the refining of copper, a solution is made containing about 2 pounds of copper sulphate and 6 ounces of sulphuric acid per gallon of water. This solution forms the elec- trolyte. The crude copper to be purified forms the anode, while the kathode con- sists of a graphitized plate of pure copper. When the current is passed, copper is dissolved from the anode and deposited in very pure form upon the kathode. Electro-typing is the process by Which reproductions are made of such articles as medals, engraved plates, busts, and so on. A reversed cast is first obtained in the usual manner, wax or gutta-percha being used for the purpose. An impression of the cast is then made in a mixture of bees-wax, Venice tur- pentine and plumbago, and the surface of this impression is covered with gra- phite, and carefully cleaned with alcohol and water. It is then submitted to a process very similar to that of electro- plating, a deposit of metal being pro- duced all over the surface of the wax, until a sufficient thickness is obtained. The metal shell, thus formed, is removed from the Avax and "backed" with metal — an alloy of V.^A, antimony, and tin being commonly used. See also Elec- tric Furnace, Electro-chemistry. ELEMI, gum resins derived from various trees. The American or Bra- zilian elemi is from Idea Icicariba, the Mexican from Elaphrium elemiferum, and the Eastern or Manila from Can- urium commune. In commercial par- lance, a brownish yellow resin, from a species of elemi, used to mix with spirit and turpentine varnishes to pre- vent their cracking as they dry. Dis- tilled with water it yields a transparent colorless oil, which boils at 166°. In pharmaceutical use elemi has an odoi like fennel, and a bitter, aromatic taste It is used to form Vnguentum elemi^ ointment of elemi, which is applied as a topical stimulant. ELEPHANT, the largest existing land animal. Its ordinary height at the shoulder is about 8 feet, but sometimes exceeds 10 feet. The weight of a large elephant is about five tons, the body being very bulky in proportion to its height. To sustain this weight it is furnished with limbs of colossal thick- ness and strength, which are also re- markably straight, each bone resting vertically on that beneath it. The flexi- bility of these limbs is sufficient to per- mit elephants to run with a speed often greater than that of the best horse. Elephants live in herds, each having a leader who gives the alarm in case of danger and decides what direction to take in escaping from an enemy. When the leader is the special mark for the hunter's attack, because he is the larg- est and has the finest tusks, the rest of the herd do their utmost to protect him. The elephant is generally one of the most inoffensive of animals, though in a state of domestication it shows a power both of remembering and resenting an injury. The favorite haunts of wild elephants are in the depths of forests — particularly in mountainous regions. Only two existing species of elephants are certainly known, the Indian (Ele- phas hidicus) and the African (Ele- phas Africanus). The amount of daily food necessary for the elephant in a state of domestica- tion may be stated, on an average, at about 200 pounds in weight. The ele- phant first became known in Europe from its employment in the wars of the East. Elephants have been taught to cut and thrust with a kind of scimetar carried in the trunk, and it was formerly usual for them to be sent into battle covered with armor and bearing towers on their backs, which contained warriors. But the principal use of the elephant in war is for carrying baggage and for