Page:The New International Encyclopædia 1st ed. v. 03.djvu/614

* BROXTOBITIS. 538 BRONZE. reornithes. (See Biro, Fossil.) It was among the tallest of known birds. It "had lejr-bones larger than those of an ox, the dninistiik measur- ing 30 inehes in length by 2V^. imhos in diam- eter, or 4j inches across the ends: while the tarsus, or lower bone of the leg to which the toes are attached, was lO'A inches long and o^A inches wide where the toes join on. Compare CJ.V.STOli-NIS. BBON'TOSAU'RTJS (Xeo-Lat.. from Gk. Bpovrii, hrontv, thunder + (inf/wf, .sawros, lizard). A gigantic herbivorous dinosaur of the svib- order Sauropoda, the fossil remains of which arc found in the upper .Jurassic strata of Wy- oming. The animal was of massive build, and attained the great length of 60 feet, with an estimated weight for the live beast of 20 tons. The trunk of the body was short and thick, the neck long and slender, the tail large and strong- ly built, and the head remarkably small. The fore limbs were as long as the hind limbs, indi- cating that the animal walked on all fours, and the feet were plantigrade — i.e. the beast walked on the flat foot, instead of on the toes ; and the footprint covered a square yard of ground. The bones of the limbs were all solid and heavily built. In this respect they resemble tlio.se of the allied genus Diplodocus. while they difter from those of the majority of dinosaurs, whose bones are hollow. The long neck of the animal was probably of much use to him for feeding upon the upper portions of the aquatic plants among which he made his home, while his great bulk and small brain indicate that he was a slow- moving beast of low intelligence. For illustra- tion of the order, see Plate Dinos.urs. BRONTOTHE'RIUM. See Titaxothebium. BRONZE (pr<)l)alily from Lat. ces Bniiidisiiim, Brundisian copper). An alloy of two or more metals, the chief ingredient always being copper, with tin ne.vt in proportion. Often zinc and lead have been used ; but if zinc is in greater propor- tion than tin, the result is not properly a bronze (see Alloy), while lead is never present in large amounts. Silver has bei-n found in the analysis of ancient bronzes, but this may have come from an imperfect smelting of the tin. The bronze tools found in ancient quarries in Fgj-pt are said to consist of 88 parts copper to 12 of tin. a hard alloy, but the supjiosed greater hardness which would have enabled stone-cvitters to work with them may have been produced by hanmiering, al- though it has l>ecn suggested that phosphorus was used and has since disappeared. (.See the paragraph treating phosphor-bremze. luider Al- loy.) The famous mixture of antiquity called Corinthian bronz.^ probably gained the l)rilliant color for which it was praised from a combina- tion of copper and tin, in some such proportion as 90 of copper to 10 of tin, without other admix- ture. Bronze is peculiar in this, that the alloy shrinks and occupies much less space than the aggregate of the separate metals. Prol)ably l)ecause of this shrinking, involving some interpenetri^tion of the atoms, it is harder than either copjier or tin. and in this respect compares with zinc. Of course it is vastly harder than lead. It has the peculiarity of filling the mold perfectly, l)eeause when melted it is very fluid — much more so than copper by it- self. Bronze is easy to work with the tool. If used in thin sheets it is one of the best metals for re- pousse work, yielding regularly and evenly, and taking from the chasing-tool a beautiful and last- ing finish. It takes from exposure to the weather, and especially to the earth in which it may be buried, a singularly beautiful green or greenish- blue color and a slightly powdery texture, which constitutes what the ancients called the arugo nobilis, and which is spoken of by the modern stu- dent as the auugo or patina. It is possible to anticipate the action of such natural causes, and to give to the surface of the bronze an artificial color, as by the use of a "pickle,' or by exposing it when red-hot to certain vapors. Thus, a jet- black patina is obtained by sulphur-fumes. The Japanese and Chinese produce ornamental bronzes, espe^'ially vases, ])latters. and the like, which are colored in clouded, mottled, and veined combina- tions, sometimes of vivid red with different shades of brown and of yellow. SometinK's these care- fully prepared decorations of the surface produce an effect similar to that of crystallization. ilECHAMCAL U.SES.' As bronze gives very per- fect castings, and is proof against the destructive property of the moisture of the air, it has been nnieh used for the supports and mountings of astronomical instruments, as in China, and for cannon. This last use was connnon in Europe during the time of the Renaissance, and bronze cannon of the Sixteenth Century are remarkable tor the beauty of their surface decoration, which includes sometimes the whole breech of the gun, and even the rings or staples which were used in earl)- days to support the gun upon its carriage. All the varieties of alloy introduced since 1850 for mechanii-al purijoses are used in the making of machinery and the like, and never or very rarely in the line arts. Use in Art. Bronze has been in use for deco- rative purposes from prehistoric times. The museums are full of bronze utensils of decorative character, representing a known ])eriod of nearly -1000 years, besides much which cannot be dated of the work of outlying and little-known civiliza- tions. The charm of ancient bronzes, Etruscan, (ireek. and Media'val. may be found very largely in the minute artistic and technical care which was given to each separate piece. The modem statuette, group, vase, or dish is commonly a mechanical reproduction of a model made by some artist whose supervision did not extend to the piece of bronze in question : but among the ancients each piece received the full atten- tion of its maker, as in the case of a carving done directly by the hand, in wood or in ivory. The a Cire Perdie Proce.ss. The art of mak- ing the bnjnze casting hollow, and so saving the material and insuring a quick and even cooling, is very ancient. It consists in putting a rough mass of the same material as the mold into the middle of it, so tluit the bronze fills only the space between them. The central core is first built up of some material ca])able of bearing heat, and this is brought to an a|)])roximate semblance of the form desired in the l)ronze. ri)on this a coat of some very fu-iible material, sui'li as wax. is placed, and is modeled by the sculptor into the perfect embodiment of his design. Upon this finished sur- face the material of the outer mold is applied in thin semi-liquid coats, each dried before the next is put on. The resulting block of clay will contain a thin mask or coat, say of wax, the out- side surface of which is the require<I work of art. The melted metal is run into this thin division