fig. g, where A, A, represents the sills; 13, 13, the breast-roll-posts; C, the cut-tree; D, D, the uprights; E, the burdown;1’, the batton; G, the reeds; H, the harness; 1, the breast-roll;K, the cheese; L, the gibbet; M, the treddles; N, the tum-blers; O, short counter-meshes; P, long counter-meshes; Q,the porry ; R, 11, cane-roll posts; S, the cane-roll; T, the weight-bar and weight; U, U, counter weights; \V, the breaking rod;X, X, cross-rods.
SILLA, a large town on the Niger , which bounded Mr. Park’stravels eastward. Lon. 1.24. W. Lat. 14. 48. N.
S1LLON, in fortification, an elevation of earth, made in themiddle of the moat, to fortify it, when too broad. It is moreusually called the envelope.
S1LLYHOW, in midwifery, a portion of the chorion, whichsometimes comes away with the child.
SILPHA, Carrion-Beetle ; in entomology, a genus of ani-mals belonging to the class insects:, and order coleopterat. An-tenns clavated; clava perfoliated ; elytra marginated; head pro-minent; thorax marginated. There are about 140 species.
S.AatMTieA, the Water-Carrion-Beetle, is brown, withgreen bronze tinge. There are four ribs on the thorax. Oneach shell there are ten stria:. The length is one-fifth of an inch.
S. Sabulosa, is black; the antenna: are short and globular,there are five strix on each shell. The shells and wings are short.There are five joints on the two first feet, four on the rest. It livesin sand.
id. Yaspillo. The margin of the thorax broad. The shellsare abbreviated, black, with two yellow belts. The thighs of thehind legs large, with a spine near their origin. Length near oneinch. It infests dead bodies. See Plate CXXXVI.
SILPHIUM, Bastard Chrysanthemum ; in botany, a gen-nus of plants belonging to the class syngenesia, and order polyga-mia necessaria; natural order, Compositx. Receptacle paleace-ous; pappus with a two-horned margin; calyx squarrose. Thereare eight species.
SILVANUS , in the mythology, a rural deity, the son of Pi-cus, king of Latiurn, and brother of Faunus , according to Virgil.Other mythologists make him the son of Mars; others of ValeriaTusculanaria, bv her own father; others of an Italian shepherd bya she-goat. He is indeed represented by painters as hail a manhalf a goat.
SILVER , in natural history, is a metal of a fine white colour,without either taste or smell; and in point of brilliancy perhaps■inferior to none of the metallic bodies, if we except polished steel.Its hardness is 7. When melted, its specific gravity is 10.478;when hammered, 10.609. In malleability, it is inferior to noneof the metals, if we except gold, and perhaps also platinum. Itmay be beaten out into leaves only inch thick. Its ducti-
lity is equally remarkable: it may be drawn out into wire muchfiner than a human hair; so fine, indeed, that a single grain ofsilver may be extended about 400 feet in length. Its tenacity issuch, that a wire of silver 0.078 inch in diameter is capable of sup-porting a weight of 187.13 lbs. avoirdupois without breaking..Silver melts when it is heated completely red hot; and whilemelted, its brilliancy is much increased. According to the calcu-lation of Bergman and Mortimer, its fusing point is 1000° of Fah-renheit. It continues melted at 28° Wedgewood, but requires agreater heat to bring it to fusion. If the heat is increased afterthe silver is melted, the liquid metal boils, and may be volatiliz-ed ; but a very strong aiid long-continued heat is necessary.When cooled slowly, its surface exhibits the appearance of crys-tals; and if the liquid part of the metal is poured out as soon asthe surface congeals, pretty large crystals of silver may Ire obtain-ed. By this method Tillct and Mongez junior obtained it infour-sided pyramids, both insulated and in groups. Silver is notoxidated by exposure to the air; it gradually, indeed, loses itslustre, and becomes tarnished; but (his is owing to a differentcause. Neither is it altered by being kept under water. But if itis kept fora long time melted in an open vessel, it gradually at-tracts the oxygen from the atmosphere, and is converted into anoxide. Macquer , by exposing silver twenty times successively tothe heat of a porcelain-furnace, obtained a glass of an olive-greencolour. Nay, if the heat is sufficient, the silver even takes fireand burns like other combustible bodies. Van Maruni madeelectric spark? from his powerful Teylerian machine pass through
a silver-wire; the wire exhibited a greenish-white flame, and wasdissipated into smoke. Before a stream of oxygen and hydrogengas, it burns rapidly with a light green flame. The oxide of sil-ver, obtained by means of heat, is of a greenish or yellowish greycolour; and is easily decomposed by the application of heat inclose vessels, or even by exposing it to the light. When silver isdissolved in nitric acid, and precipitated by lime-water, it falls tothe bottom under the form of a powder, of a dark greenish browncolour. From the experiments of Wenzel and Bergman it fol-lows, that the greenish or yellowish grey oxid is composed ofabout 90 parts of silver and 10 of oxygen. When this oxide is ex-posed to the light, part of its oxygen is separated, as Scheele firstascertained; and is converted into a black powder, which containshut a very small portion of oxygen, and may be considered as sil-ver reduced. By exposing the solution of silver in nitric acid tosunshine, the silver precipitates in the form of a flea-brown pow-der. Neither carbon nor hydrogen has been combined withsilver, nor does it combine witli the simple incombustibles; butit combines readily with sulphur and phosphorus. Silver alsoreadily combines with the greater number of metallic bodies. Forthe affinities of silver, see Chemistry.
~ Silver-Leaf , that beaten out into fine leaves for the useof the gilders, which is performed in the same manner as gold-leaf.
Silver , Shell, is prepared of the shreds of silver-leaves, or ofthe leaves themselves, for the use of painters, after the same man-ner as shell-gold.
Silvering. The art of silvering wood, paper, Sec. is perform-ed in the same manner as gilding, making use of silver instead ofgold-leaf.
Silver Copper or Brass, clean the metal with aquafortis,by washing it lightly, and then throwing it in water; or by scour-ing it with salt and tartar with a wire-brush. Dissolve some silverin aquafortis, and put pieces of copper into the solution; this willthrow down the silver in a state of metallic powder. Take twentygrains of this powder, and mix with it two drachms of tartar, thesame quantity of common salt, and half a drachm of alum; rubthe articles with this composition till they are perfectly white, thenbrush it off, and polish them with leather.
To Silver the Dial-Plates or Clocks, Scales of Ba-rometers, &c. Take half an ounce of silver-lace, add to it anounce of double refined aquafortis, put them into an earthen pot,and place them over a gentle fire till all is dissolved, which willhappen in about five minutes; then tqke them off, and mix it ina pint of clear water, after which, pour it into another clean vessel,to free it from grit or sediment; then add a spoonful of commonsalt; and the acid, which has now a green tinge, will immediatelylet go the silver-particles, which form themselves into a whitecurd; pour off the acid, and mix the curd with two ounces ofsalt of tartar, half an ounce of whiting, and a large spoonful ofsalt, more or less, according as you find it for strength. Mix itwell up together, and it is ready for use. Having well cleared thebrass from scratches, rub it over with a piece of old hat and rot-lenstone, to clear it from all greasiness, and then rub it withsalt and water with your hand: take a little of the before men-tioned composition on your finger, and rub it over where the salthas touched, and it will adhere to the brass, and completely silverit. After which, wash it well with water, to take olt what aqua-fortis may remain in the composition; when dry, rub it with aclean rag, and give it one or two coats of varnish. This silver-ing is not durable, but may be improved by heating the article,and repeating the operation till the covering seems sufficientlythick.
Silver-Plating. The coat of silver applied to the surface ofI he copper by the means mentioned above, is very thin, and isnot durable. A more substantial method of doing it is as follows:Form small pieces of silver and copper, and tie them together withwire, putting a little borax- between. The proportion of silvermay be to that of copper, as 1 to 12. Put them into a white heat,when the silver will be firmly fixed to the copper. The whole isnow made to pass between rollers till it is of the required thick*ness for manufacturing the articles required.
S1LVES, a town of Portugal, 15 miles E, N. E. of Lagos , and39 W. of Tavira.
S1LUR1S, in ichthyology, a genus belonging to the order**