Perhaps even more important from a scientific point of view, is J. B. Hannay's discovery resulting in the artificial formation of the diamond. For the many unsuccessful preliminary experiments, the reader is referred to his interesting paper read before the Royal Society. The only successful result was obtained in the following manner. A coil-tube of Lowmoor iron, measuring 20 in. long, 4 in. diameter, and in. bore, was f-filled with a mixture containing 90 per cent. of bone-oil (the nitrogenous distillate obtained in the manufacture of bone-charcoal), taking only the portion boiling at 115°-150° (239°-302° F.), and rectified over solid caustic potash, and over sodium ; 10 per cent. of paraffin spirit boiling at 75° (167° F.) ; and 4 grm. of lithium. The tube was closed by welding, and was then heated in a furnace to a visible red heat for 14 hours, and allowed to cool slowly. On opening the tube, a great volume of gas was given off, and very little liquid remained. At the end which had been uppermost (obliquoly) in the furnace, was a bard, smooth, adherent mass, which, when removed and pulverized, disclosed microscopic fragments of crystalline carbon, differing from natural diamond in no respect save brilliancy. Thus, though a great achievement scientifically, the cost and difficulty of the process, and the insignificant value of the product, preclude at present its commercial application.
Diamond (Fe., Diamant ; GER., Diamant, Demant).—Composition, pure carbon ; hardness, 10 ; sp. gr., 3.515-3'525; varies from colourless transparency to white, grey, brown, red, yellow, green, blue, and even black.
In Europe, diamonds are of rare occurrence. A very doubtful one is said to have been picked up in Ireland, another was found at Dlaschkowitz, in Bohemia, and numbers of small ones, the largest not 8 carats, occur in the gold washings near Bissersk, on the western side of the Urals, in a mioa-slate formation.
Tho diamond-fields of Asia were formerly of considerable importance, notably those of India, and though now almost abandoned, and affording but a poor return to the few diggers engaged, they would probably repay systematic and scientific exploration. Diamonds have been found. in the Ganges Valley ; are still washed as far north as Sambalpir, and in the Majnodi, an influent of the Mahanadi ; on the Upper Nerbudda ; on the line of the Godavery ; and on the course of the Krishna. The extreme points of this district would be Masulipatam and the Ganges Valley, embracing some 90,000 sq. miles. The most southern group of diamond strata is about Cuddapah on the Penner, and at Condapetta and Ovalumpally ; also at Landur and Pinchetgapadu, and still farther beyond the Penner Valley to Gandicotta and Gutidrug. The strata here are :—topmost, ft. of sand, grit, and loam, followed by 4 ft. of tough blue-black muddy earth, restiog upon the diamond bed, 2-2i ft. thick, consisting of rounded pebbles (much hornblende) and grit, bound together by loam. The next group is 15 miles northwards, on the west side of the Nalla-Malla Hills ; the beds hero are only about 1 ft. thick. A third group, of greater magnitude, is that of Ellora, on the Lower Krishna, and embracing the so-called Golconda diggings, from the fort of that name, where the stones are brought for sale. The chief finds are at Mallivully, about
6-7 hours W.-S.-W. of Ellora, and at Partial, near Condapilly, on the N. bank of the Krishna. Here the diamonds occur in alluvium 20 ft. deep. The Sambalpir group lies in the bed of the Mahanadi, from Chunderpore to Sonepore, about 24 miles. The best is mostly tough reddish clay, with pebbles and a little sand. The Ganges group lies in a sandstone range, southward of that river, principally at Myra, Etawa, Kamaruja, Brijpur, and Baraghari. In India, the dry grounds are worked by sinking shallow pits to reach the diamantiferous stratum, and the latter is broken up before being subjected to the common washing process for removing the earth. Among other Asiatic countries, China possesses diamonds in the streams and sands from the Chiukang-ling range, about 15 miles S.-E. of Yichow-fu, in Shantung. Their size varies from that of a millet-seed to a pin's head. Numbers of diamonds, some of great size and purity, occur in the Ratoos Range, in the S.-E. of Borneo, in a sand and gravel bed about 6 ft. thick, resting on serpentine, and overlaid by 30-40 ft. of red clay ; in Landak, in the N.-W. part of the island, they are also found.
Africa recently hold the foremost position among diamond-producing countries. and still continues to furnish very large supplies. The fields lie chiefly in the Colony of Griqualand West, in the valleys of the Vaal, Modder, Veit, Orange, and other rivers, draining the Drakenberg (Quath lamba) Mountains. The area proved to be diamaotiferous is already very large, though but little has been done to determine its limits. The stones are sought in two distinct formations—in the recent alluvial deposits of the river-valleys ; and in "pans" or basins of considerable depth (commonly 100-200 ft.),containing a peculiar igneous conglomerate. Throughout this mass, diamonds are scattered with greatly regularity. It is broken down, suffered to bake in the sun for several days, and then washed in " cradles " or "long-toms," such as are employed in alluvial gold-mining. Great variety of character is to be noticed in the stones from different localities : those from the river-sands are waterworn, but the whitest of any, and bring the best prices ; those from Dutoit's Pan are large, off-coloured and yellow ; those from Bultfontein are small bevelled octahedrons, pitted on the surface ; those from Kimberley are smaller and whiter than those from Dutoit's Pan. About 10 per cent. are of 1st quality, 15 of 2nd, 20 of 3rd, and the remainder merely " bort," and not reckoned as gems. Their colour is classed as " white," " Cape white," bye-water," " off colour," and " yellow." The total value of the diamonds taken from these diggings is estimated at 15,000,0001. The returns of the exports, which, of course, understate the truth, are :—in 1868, 1, value 1501. ; 1872, 45,830, value 306,0411 ; falling, in 1877, to 83, value 3301.