Page:The American Cyclopædia (1879) Volume X.djvu/167

 LAPIS LAZULI LAPITH^E 161 charged with it around the extreme edge, and it is carefully renewed as required. It is more economical for this use, and applied to the sur- faces of other mills for grinding the facets of hard stones, than emery ; but the latter powder with water is employed for the more common class of stones. It is used of various degrees of fineness, and in such quantity that there shall always be a loose portion of it between the stone and the metallic surface of the lap. Polishing is effected by successively using finer and finer powders. The hardest small stones are finished on laps of copper or of pewter, and others on lead, and the powder used is rotten stone, which is plentifully applied with water. To make it adhere, the face of the metal is hacked in lines with the edge of a knife. For very soft stones, as alabaster, after these are smoothed upon a lead or wood mill with flour emery, the list mill is employed with pumice stone and water, and after this the buff leather disk with fine putty powder and water. The last polish is sometimes given with the hand and putty powder. In the East Indies, wheels and rubbers are made of corun- dum or emery imbedded in lac resin. For the former about one third of the bulk is lac resin and two thirds is the powder. This is carefully stirred, a little at a time, into the melted resin; the mass is then kneaded and rolled upon a stone slab upon which fine corundum powder is sprinkled, and finally it is flattened into a disk with an iron rolling pin. The wheels are made of different degrees of fineness, and when used are set upon a horizontal axis, which the workman, sitting on the ground, causes to re- volve with a spring bow, holding the stone in his left hand against the wheel, which is oc- casionally moistened and sprinkled with co- rundum powder. The rubbers contain a much smaller proportion of corundum ; and the finest have intermixed the grindings of agates, carne- lians, &c. Grindstones are used for giving shape to gems only in the works at Oberstein on the Nahe in Germany, where agates are fashioned into the form of various articles, as buttons, clasps, "stamps, paper weights, mortars for chemical purposes, &c. Stones of large size are run by water power, and the workmen lie down in front of them when at work, the body being supported by a sort of stool. They acquire wonderful dexterity in giving the shape they desire to the hard stones, and produce with extraordinary rapidity playing marbles of perfectly globular form. For full details of the processes of the lapidary, vol. iii. of Holtzapffel's " Mechanical Manipulations " may be consulted; also "A Popular Treatise on Gems" (New York, 1859-'67), by Dr. L. Feuchtwanger, and " Diamonds and Precious Stones" (frew York, 18Y4), translated from the French of Louis Dieulafait by F. Sanford. (See also DIAMOND, and GEM.) LAPIS LAZULI, Lazulite, Ultramarine, or Blue Spar, a mineral distinguished for its beautiful azure-blue color, highly esteemed as an orna- CONSTITU- ENTS. 1. 2. 3. 4. Silica 35-8 46-0 46-50 45-604 Alumina Soda Carb. lime Sulphate lime. Sulphur Oxide of iron. Chlorine 84-8 23-2 8-1 3-1 14-5 28-6 6-5 -j 3-6 81-76 9-09 8-52 <>3-} 5-89 0-95 018 0-42 23-304 21-476 Potash, 1-752 ^[3-880 1-685 Iron, 1-063 trace Loss 2-0 1-69 Lime 0-021 Total 100-0 100-0 100-00 98-735 mental stone. It is commonly obtained of massive form, and of compact or granular structure. Crystals, which are rare, are 12- sided ; a fine specimen of the regular dode- cahedron with mirror-like faces is contained in the collection of the French school of mines. The mineral is a silicate of soda, lime, and alumina, with a sulphide, probably of iron and sodium. The analyses give variable results. That by Clement and Desormes, the first of those below, is regarded as giving the true composition; by following it, artificial ultra- marine, a pigment formerly prepared directly from the mineral, has been successfully manu- factured. The fourth, by Varrentrapp, is of an artificial ultramarine. The second analysis is by Klaproth, and the third by Varrentrapp, as given by Dufrenoy (Mineralogie) : The hardness of the mineral is 5-5 ; specific gravity 2*38, crystals 2'959. When melted by the blowpipe it loses its blue color; but a variety from Chili recovers it on cooling after calcination. Lapis lazuli occurs in calcareous rocks, associated and sometimes mixed with mica and iron pyrites. It is brought from Persia, China, Lake Baikal in Siberia, Bokhara, and recently from Chili and California. In trade it is known as the Armenian stone. The principal use of the stone has been for making the blue ultramarine pigment ; and as from the best stone only 2 to 3 per cent, can be obtain- ed, the cost of the purest article is sometimes over $100 an ounce. The artificial prepara- tions, however, are now very generally sub- stituted. (See ULTEAMAKINE.) Lapis lazuli was employed by the ancient gem engravers, and the fine specimens have ranked among choice jewels. The stones through which the mineral is disseminated are carved into many orna- mental objects, as vases, snuff boxes, cups, and even architectural ornaments. In the Orloff palace at St. Petersburg are apartments lined with lapis lazuli. Imitations of it are made of bone ashes colored with oxide of cobalt. LAPITHJE, in Grecian legends, a people of the mountains of Thessaly, descended from Lapithes, the son of Apollo and Stilbe. They were governed by Pirithous, the son of Ixion, and are famous for their battles with the centaurs, who, being likewise sons of Ixion, claimed a share in their father's kingdom. The wars having been closed by a peace, Pirithous