Fine ivory is known by having no cracks nor flaws, whether in the solid or in the hollow ; their presence is a serious detriment. Tusks that taper very gradually are preferred, and those whioh have a small hollow, i. e. are as straight as possible. Sharply-tapering and much-bent tusks cause great waste in cutting up. Tusks damaged at the point are inferior, and depreciated internally. The coat should be fine, thin, clear, and transparent. The applications of ivory include almost all ornamental articles of turnery, as well as knife-handles, brush-backs, combs, piano-keys, &c. " Scrivelloes," or tusks weighing less than 20 lb., are principally converted into billiard-balls. The ivory for piano-keys, combs, and other square articles, is cut into shape by means of very fine circular saws. The goods are polished and bleached. The latter operation is performed either by exposure to sunlight for periods varying from 4 weeks to 6 months. or by immersion in turpen tine (kept near the surface), accompanied by exposure to sunlight for 3-4 days. When bleached the ivory may be dyed. For ordinary dyestuffs, it will need to be first mordanted by soaking for 6-8 hours in vinegar, or alum solution. Red may be produced by a decoction of peach-wood ; yellow, by saffron ; green, by a solution of 3 parts verdigris and 1 part ammonia in vinegar ; blue, by fel: lowing the green bath with potash lye ; black, by logwood decoction and acetate of iron. Coal-tar colours may also be used. Ivory is silvered usually by immersion for a few minutes in a nitrate of silver bath, and then in clean water exposed to the sun ; or by exposure to the fumes of phospho retted hydrogen after the silver bath. It may be made flexible by immersion in pure phosphoric acid, of sp. gr. 1.13 ; it hardens again on exposure to the air, but resumes pliancy when put into hot water.
or Fossil tusks of the extinct Elephas primigenius, or mammoth, have a bolder and more extensive curvature than those of E. indicus. The numerous specimens which have been discovered may be ranged under two averages of size—the larger at 91 ft. long, the smaller at 5i ft. Prof. Owen aaaigns the smaller to the female animal, and thus makes the mammoth more nearly allied to the African than the Indian elephant of the present. This extinct elephant roamed in countless herds over the temperate and northern parts of Europe, Asia, and America, and its remains are now found in great abundance in Siberia and Alaska, preserved in the frozen soil. The erosion of the soil along the banks of the great rivers feeding the Arctic Ocean discloses every year very large quantities of this fossil ivory, the chief centres for ita barter being Yakutsk; on the Lena, Turuchansk, on the Jenesei, and Obidorsk, on the Obi. Numbers of tusks are also found scattered about on the Tundras ; while the richest harvest of all is gathered from the New Siberia Islands. Probably the total annual production of fossil ivory in Asiatic Russia amounts to 20,000 30,000 lb., the average weight of a pair of tusks being placed at 200 lb. The largest rarely have the country, being either too rotten for industrial purposes, or so heavy that the natives are obliged to saw them up for removal. This latter fact causes great waste of the material. The tusks were
an article of export to China at least 7 centuriea ago, and no signs are yet visible of any diminution in the supply. Some were sold in London in 1876 at prices varying from 22/. to 43/. a cwt. Recent explorations on the Yukon river, in Alaska, are said to indicate the existence of even larger quanti ties of fossil ivory than have been yielded in Siberia.
hippopotamus, or " sea-cow " (Hippopotamus amphibius), is a native of Africa, in some parts of which, it is found in great abundance. The teeth of this animal which possess commercial value are of two kinds—the " canines," and the " incisors." The former are 4 in number, 2 in each jaw ; those of the lower jaw are the larger ; both are much curved. They are composed principally of an extremely dense, compact kind of dentine, protected on the most exposed portions of the surface by a thick layer of enamel, so hard as to strike fire with steel. The incisors number 8, are various in size, but all smaller than the canines, and are of less value. Usually only the two lower, lateral, projecting incisors are imported. The larger proportion bf mineral matter in the dentine of the oaninea, as compared with elephant- or walrus-ivory, and its great density of formation, render it harder, and less liable to receive stains, than other similar substances, whilst the smaller amount of organic matter, and the almost complete absence of oily particles, account for its superior and delicate whiteness. These latter qualities, on the other hand, induce a certain brittleness, and render it easily acted upon by organic acids. The enamel is still whiter and harder than the dentine. Formerly, the canines were largely used by dentists, for making artificial teeth ; but they have latterly been replaced by substitutes less liable to destruc tion by the acids met with in the act of eating. They are much employed in France, far the pro duction of delicate intaglios ; they are also superior to ivory for handles of surgical instruments, &o. For all but dental purposes, the enamel is first removed by an acid bath. The incisors are too soft to be of any value to dentists ; the two long lower ones are made into knitting- and netting needles, and similar articles. The smaller and curved upper incisors are fit only for common turnery. At one time, we imported 7-10 tons annually, worth up to 30s. a lb ; the quantity now is email, and the value only ls. 6d.-2s. 6d. a lb.
walrus, or " sea-horse" (Trichecus Rosmarus[Rosmarus obesus]) is a native of the Arctic regions, being found abundantly on the coasts and islands of Alaska, where some 50,000 are obtained every year by the American whalers. The tusks of the animal are limited to a single pair, growing from the upper jaw, and descending outside the lower jaw. Their substance is less dense and coarser than the dentine of the hippopotamus tusk, and is of proportionately less value in commerce. They weigh about 4 lb. a pair, and sometimes attain a length of 2 ft. They were formerly in demand for dental purposes, and are much used in Chinese turnery. The quantity annually produced in Alaska amounts to about 100,000 lb.; and the Hudson's Bay Co. sometimes import 100-200 lb. in a year.