with a proper quantity of alkaline flux. The sulphurated oxide of silver and antimony may be treated in the same way. See ASSAYING. Silver is of a fine white colour and great brilliancy. The specific gravity is 10.4, and according to some, when it is hammered, 10.5, and sometimes nearly 11. The hardness of silver is intermediate between iron and gold. The elasticity of silver is considerable, and it is one of the most sonorous of the metals. It possesses very great ductility and malleability. It may be beaten out into leaves of of an inch thick, and a grain of silver may be so extended, as to be formed into a hemispherical vessel of sufficient capacity to hold an ounce of water, or to be drawn out into a wire four hundred feet in length. The tenacity of silver is very great. A wire .078 of an inch in diameter will support a weight of one-hundred and eighty-seven pounds avoirdupois. Silver is a good conductor of caloric. Its expansive power is less than that of lead and tin, and greater than that of iron. When it is exposed to a white heat it melts. The temperature necessary to bring it to fusion has been calculated at the 1000° of Fahrenheit; but, according to Kirwan, it requires a higher temperature than 28° Wedgewood to melt it, although at that temperature it continues in a state of fusion. When it is cooled slowly after fusion, it exhibits some marks of crystallization. It assumes the form of four-sided pyramids or of octahedrons. If the heat be increased after the silver is melted, it boils, and may be reduced to vapour. The surface of melted silver is so extremely brilliant, that it seems to throw out sparks, which is called coruscation by the workmen. Silver is a good conductor of electricity. It has no perceptible taste or smell. Silver is not altered by exposure to the air, although it is soon tarnished, which is owing, as Proust ascertained, to a thin covering of sulphuret of silver, which is formed by sulphureous vapours to which it is exposed; but when it is subjected to a strong heat for a long time, in an open vessel, it combines with the oxygen of the atmosphere, and is converted into an oxide. In the experiments of Macquer, the oxydation of silver was effected by exposing it for twenty times successively, in a crucible, to the strong heat of a porcelain furnace. At last perceptible traces of oxydation were observed, and a vitreous matter of an olive colour was ob. tained. In other experiments silver being acted on by the heat of a burning-glass was covered with a white powder, which was afterwards converted into a crust of a green colour. Van Marum passed electric shocks through silver wire, which was instantly reduced to a kind of powder, with a greenish white flame, and the oxide which was formed was dissipated in vapour. The oxide of silver, which is formed by these processes, is of a greenish or yellow colour. It is composed of about ten parts of oxygen, and ninety of silver. The oxide of silver is very easily reduced, for the affinity of oxygen for this metal is very feeble. It is decomposed by the application of heat, and even when it is exposed to the light. By heating it in close vessels, pure oxygen gas is obtained, and the metal is converted to the metallic state, by melting it in a crucible. Silver combines with phosphorus, forming a phosphuret. One part of silver in filings, with two of phosphoric glass, and half a part of charcoal, exposed to heat in a crucible, yielded a phosphuret of silver, which had acquired one-fourth of its primitive weight of silver. This phos phuret is of a white colour, brittle, of a granulated texture, and may be cut with a knife. By throwing pieces of phosphorus on silver red hot in a crucible, the metal is instantly melted, and the phosphuret which is formed remains at the bottom. At the moment when the surface becomes solid, a quantity of phosphorus is thrown out with a kind of explosion, and the surface of the metal then exhibits a mamellated appearance. Pelletier, who first made this experiment, concludes from it, that silver is susceptible of retaining a greater proportion of phosphorus, in combination with it, when it is in fusion, than in the solid state, and that the separation of the phosphorus is owing to the sudden contraction of the silver. A hundred parts of silver in fusion retain twenty-five of phosphorus, but only fifteen when it becomes solid. Phosphorus has the property of reducing the oxides of silver, and of precipitating them from this solution in acids, in the metallic form. Sulphur combines readily with silver, both in the dry and humid way. By stratifying in a crucible, plates of silver alternately with sulphur, and melting them rapidly, a deep violet-coloured mass is obtained, which is more fusible than silver, brittle, crystallized, and has a metallic lustre. It may be cut with a knife, and has a good deal of resemblance to vitreous ore of silver. When this sulphuret of silver is exposed to heat for a considerable time, the sulphur is gradually dissipated, and the silver remains pure and ductile. Sil. ver combines very readily with sulphur, when it is long exposed to those matters which gradually deposit this substance. This effect is immediately produced when silver is brought into contact with sulphurated hydrogen gas, or when it is immersed in water, impregnated with this gas, as in natural sulphureous waters. Dr. Thomson thinks it is owing to the same cause, that a silver spoon is tarnished by a boiled egg, and particularly if the egg has begun to spoil. Sulphuretted hydrogen gas, which is exhaled by the egg, is decomposed; the sulphur combines with the silver, and forms a thin layer of sulphuret of silver, which is of a dark or violet colour; other writers have ascribed this to the action of galvanism. The same thing happens when silver is exposed in places that are much frequent ed, as in churches and theatres. forms alloys with most of the metals, and salts with the acids. Hence its use in coinage, and also in medicine. Silver Antimonial silver, in colour, is between silver white and tin white; sometimes inclining more to the one, sometimes more to the other. It occurs massive, disseminated and crystallized. Specific gravity between 9 and 10. Heated on charcoal before the blow-pipe, the antimony is volatilized with the odour peculiar to it, and there remains a mass of silver, surrounded with a brown slag. It consists, according to Vauquelin, or Before the blow-pipe the arsenic and antimony are volatilized, and they emit a garlic-like smell. The silver remains more or less pure in shape of a globule. This is a very rare mineral, and does not tarnish so quickly as native arsenic; it passes on the one side into native arsenic; on the other into native silver. SILVERING, in the arts, consists in covering the surfaces of substances with a thin coating of silver; either for the purpose of beauty, silver being so much more handsome than the inferior metals; or, on account of its superior wholesomeness, compared with copper, brass, or lead, for culinary purposes, it resisting the corroding power of vinegar and other weak acids. The metals that are usually covered with silver are, copper and brass, and sometimes iron, and there are three distinct modes of performing the operation. 1. Silvering, by amalgamation, is thus performed: to a solution of nitrated silver add some plates of copper, which will throw down the silver in its metallic state, and very finely divided; scrape it from the surface of the copper, wash it well and dry it. Of this powder take half an ounce, of common salt and sal ammoniac two ounces, and of corrosive sublimate one drachm, rub them well together, and make them into a paste with a little water. Then take the vessel to be silvered, and clean it by means of a little very dilute aquafortis, or by scouring it with a mixture of common salt and tartar. When it is perfectly clean, rub it with the above-mentioned paste till it is entirely covered with a white metallic coating; this coating is an amalgam produced by the decomposition of the corrosive sublimate, by means of the copper, to the surface of which it applies very closely and expeditiously. The copper, being thus silvered over, is to be washed, dried, and afterwards heated nearly red, in order to drive off the mering firmly to the copper, and capable of cury; the silver remains behind, adherbeing highly polished. 2. Silvering by luna cornea. the usual manner, by pouring a solution Prepare the luna cornea in of common salt into nitrate of silver, as long as any precipitation takes place, and boiling the mixture; the white curdy matter, thus obtained, is to he mixed with three parts of good pearlash, one part of washed whiting, and somewhat more than one part of common salt. The surface of the brass, be. ing cleared from scratches, is to be rub. bed with a piece of old hat and rotten stone, to remove any grease, and then is to be moistened with salt and water; a little of the composition being now rubbed on with the finger, the surface of the metal will presently be covered with silver. Then wash it well, rub it dry with soft rag, and, as the coat of silver is extremely thin, cover it with transparent varnish, to preserve it from tarnish. This kind of silvering is very imperfect, and is only used for the faces of clocks, the scales of barometers, and similar objects. 3. Silvering by silver in substance. There are three ways of performing this. The first is, by mixing together twenty grains of silver, precipitated by copper, two drachms of tartar, two drachms of common salt, and half a drachm of alum; this composition being rubbed on a perfectly clean surface of copper or brass will cover it with a thin coating of silver, which may afterwards be polished with a piece of soft leather. A still better way is that which is called French plating, which consists in burnishing down upon the surface of the copper successive layers of leaf-silver to any required thickness. In this the silver has much more solidity than in any of the former, but the process is tedious, and the junctures of the leaves of silver cannot always be entirely concealed. The English method of plating (in those works to which it is applicable) appears to be the best of all. It is thus performed: one of the surfaces of an ingot of copper is rendered quite smooth and clean, and is sprinkled over with glass of borax; upon this is laid a plate of fine silver, about one-twelfth of the weight of the copper, and the two are carefully bound together by wire; the mass is now exposed to a full red heat, which melts the borax, and causes the silver to adhere to the copper; the ingot is now passed through a rolling press, and formed into a plate; both the silver and copper extending uniformly during the whole process, at the conclusion of which, the two metals are inseparably fixed to each other. See Aikin's Dictionary." SILURUS, the silure, in natural history, a genus of fishes of the order Abdominales. Generic character: head large, naked, and depressed; mouth extremely wide, and furnished with long feelers or tentacula; eyes small, body lengthened, naked; first ray of the pectoral or dorsal fin serrated with reversed spines. There are twenty-nine species, of which the following most deserve notice. S. glauis is generally about three feet long, though it has been seen of twelve, and of the weight of three hundred pounds, and consequently is one of the very largest of European river fishes. It is most plentiful in the north, is seldom seen in motion, and commonly lies ingulfed in mud at the bottoms, with its mouth open, and its long tentacula moving about in every direction. These last. being similar in appearance to worms, are mistaken for such by many fishes, which are, by this deception, drawn within the jaws of destruction. Its flesh is used for its cheapness, rather than its excellence, and its skin, by some simple process, is converted into a hard, transparent substance, which accomplishes the purposes of horn and glass. SIMIA, the ape, in natural history, a genus of Mammalia, of the order Primates. Generic character: front teeth in each jaw four, near together; canine teeth solitary, longer than the others, distant from the grinders; grinders obtuse. Animals of this genus are commonly divided into such as have no tails; such as have only very short ones; such as have very long ones; and, lastly, such as have prehensile tails, with which they can lay hold of any object at pleasure. These four classes are called respectively apes, baboons, monkeys, and japajous. In the whole genus there are enumerated by Gmelin sixty-three species, of which we shall notice some of the most important. S. satyrus, or the orang-outang. This animal is said to grow in its native woods of Africa and India to the height of six feet, and to subsist, like most other species, on fruits. It flies from the haunts of mankind, leads a solitary life, and displays great strength, agility, and swiftness, which render it extremely difficult to be taken. It has been known to attack and destroy negroes wandering at a distance from their habitations, and to carry off women to its wretched habitation, watching them with such extraordinary vigi. lance, as scarcely to admit the possibi lity of their escape. Its general resem. blance to the human figure and countenance, is particularly and mortifyingly strong, yet minute observation and dissection have pointed out almost innumerable differences, the detail of which is here impossible. It is capable of being tamed and domesticated, and many years since, one was exhibited in London, which had been disciplined to sit, and work, and eat like a human being, using a knife and fork for the latter purpose. Its disposition was pensive; its manners were gentle; and it appear ed to possess, for its keepers, and those to whom it had been long familiarized, a high degree of genuine gratitude and attachment. For the orang-outang, see Mammalia, Plate XIX. fig. 1. S. inuus, the Barbary ape, is about four feet in height, and is the species most commonly exhibited in public shows, and is trained to the performance of a great variety of tricks, calculated to attract popular admiration. The discipline it passes through is often severe, and this species is considered, in its natural state, as being more ferocious, and less sagacious, than several others of the class. See Mammalia, Plate XIX fig. 2. S. sphynx, or the great baboon, is between three and four feet high, of a grey brown colour, and is particularly muscular in the upper part of its body; its hands and feet have sharp nails, like claws; but on its thumbs there are nails formed like those on the human fingers. It is an animal incapable of domestication, and has, in no instance, been observed to be divested of great malignity and fierceness of disposition. The female produces only one young one at a birth, which she suckles at her breast, and carries about with her in her arms. Baboons inhabit the hottest climates of Africa, and are often seen in very considerable numbers. The plantations of fruits and roots are frequently much injured by their depredations. They are scarcely, in any species, susceptible of attachment. In confinement, they display incessant restlessness and irritation, and in their form and manners they present a complication of ferocity and hideousness. See Mammalia, Plate XIX. fig. 3. S. hamadryas, or the dog-faced baboon, is very large, and often greater than the common baboon. It is distinguished by a vast quantity of hair, spreading from each side of the head down the shoulders, and covering the animal to the waist, like a mantle. Its colour is a mixture of grey and brown. It is a ferocious and danger. ous animal, is found in the most torrid regions of Africa, and though more rare than the common species, is yet seen occasionally in large companies. Its general aspect, when in an undisturbed state, is that of profound meditation; but when molested, its looks indicate the most perturbed and malignant feelings. In confinement, it is turbulent, untractable, and filthy. The tail of this baboon is nearly as long as its body. S. leonina, or the leonine monkey, is supposed to be an inhabitant of Abyssinia, and is two feet in length, from the nose to the tail; along the face is a great quantity of long hair, extending nearly from the eyes back over the forehead and crown of the head, and from the chin over the neck, and this bushment of hair gives it, in addition to the general form and countenance of the animal, no slight resemblance to the lion, from which it derives its designation. See Mammalia, Plate XIX. fig. 4. S. mona, or the varied monkey, is one of the largest species, and is nearly two feet in length. It is found in various parts of Africa, and differs much in individuals in respect to colours, which are sometimes bright, and at others dull. In general it is of a dark olive-grey. See Mammalia, Plate XIX. fig. 5. S. nasalis, or the proboscis monkey, is one of the most curious in its aspect, and most ludicrous of the class. It is about two feet in length. The face is of an incurvated form, and of a brown colour, and the nose, which is its great singularity, is of such a length and shape, as to give the animal an appearance highly grotesque. By a groove or furrow running down it, from the beginning to the tip, it is nearly divided into two lobes, and on a side view its extreme projection is nearly as striking and singular, as the former circumstance renders a full one. It is found in the East Indies, where, however, it is somewhat rare. It is said to be more numerous in Cochin China. It feeds on fruits, and is highly untractable and savage. S. beelzebul, or the preacher monkey, is as large as a fox, and is extremely common in the woods of Brazil. Travellers have stated that it is usual for one of these to ascend a tree, and, by certain sounds, to collect vast multitudes beneath him, when he commences a howl, so loud as to be heard to a vast distance. After this has continued for some time, he, by a particular signal, induces those around him to join in the noise, which then becomes most hideous and intole rable. This united clamour at length ceases, and the original howler again proceeds undisturbed in his address. The throat bone of this monkey appears, from dissection, to be particularly constructed for the utterance of strong sounds. The S. seniculus, or royal monkey, is about the size of a squirrel, and inhabits the damp woody districts of Cayenne, being never found on the mountains. In its sounds and manners, it resembles the last species. In the morning and evening, and sometimes on several occasions in the interval, these animals produce such rattling, terrific, and varied noises, as excite the idea of every native of the forest being in open cry. And even the sounds of a single one are so powerful as to impress the idea of peril very strongly on the hearer. These creatures are ex tremely tenacious of life. They will of ten sustain parts of several discharges from guns, before they drop from the tree, which they cling to with the last efforts of existence, sometimes, indeed, maintaining their hold, it is said, by the hands and tail even after death. The two last species belong to the class of monkeys with prehensile tails, or japa jous. The greater number of the animals of this comprehensive genus are said to be remarkably fond of snuff, mustard, and tobacco, which they will eat in considerable quantities. A great number of species are furnished with cheek-bags, or pouches, where they may deposit, for the convenience of carriage, a supply of food, which will last for several days after they have finished. their immediate repast. Monkeys are, in some parts of Africa, used for food, and several species are said to be excellent and delicate for this purpose. SIMILAR, in arithmetic and geometry, the same with like. Those things are said to be similar, or like, which cannot be distinguished but by their compre sence, that is, either by immediately applying the one to the other, or some other third to them both, so that there is nothing found in one of the similar things but is equally found in the other, notwithstanding their similitude may differ in quantity; and since, in similar things, there is nothing wherein they differ besides the quantity: quantity itself is the internal difference of similar things. In mathematics, similar parts have the same ratio to their wholes, and if the wholes have the same ratio to the parts, the parts are similar. See PART. Similar angles are also equal angles. In solid angles, when the planes under which they are contained are equal, both in number and magnitude, and are disposed in the same order, they are similar, and consequently equal. Similar arches of a circle are such as are like parts of their whole circumferences, and consequently equal. Similar plane numbers are those numbers which may be ranged into the form of similar rectangles, that is, into rectangles whose sides are proportional; such are 12 and 48; for the VOL. XI. sides of 12 are 6 and 2, and the sides of 48 are 12 and 4: but 6: 2:: 12: 4, and therefore those numbers are similar. Similar polygons are such as have their angles severally equal, and the sides about those angles proportional. Similar rectangles as those which have their sides about the equal angles proportional: hence, 1. All squares are similar rectangles. 2. All similar rectangles are to each other as the squares of their homologous sides. Similar right-lined figures are such as have equal angles, and the sides about those equal angles proportional. Similar segments of a circle are such as contain equal angles. Similar curves: two segments of two curves are called similar, if any right-lined figure being inscribed within one of them, we can inscribe always a similar right-lined figure in the other. Similar conic sections: two conic sections are said to be similar, when, any segment being taken in the one, we can assign always a similar segment in the other. Similar diameters of two conic sections: the diameters in two conic sections are said to be similar, when they make the same angles with their ordinates. Similar solids are such as are contained under equal numbers of similar planes, alike situated. Similar triangles are such as have their three angles respectively equal to one another: hence, 1. All similar triangles have the sides about their angles proportional. 2. All similar triangles are to one another as the squares of their homologous sides. SIMILAR bodies, in natural philosophy, are such as have their particles of the same kind and nature with one another. SIMILAR figures, in geometry, such as have their angles respectively equal, and the sides, about the equal angles, proportional. SIMILAR parts, in anatomy, are those parts of the body, which, at first sight, appear to consist of like parts, or parts of the same nature, texture, and conformation; of these we usually reckon ten, viz. the bones, cartilages, ligaments, membranes, fibres, nerves, arteries, veins, flesh and skin. SIMILE, or SIMILITUDE, in rhetoric, a comparison of two things, which, though different in other respects, yet agree in some one. The difference between a simile and comparison is said to consist in this, that the simile properly belongs to whatever we call the quality of the thing, and the comparison to the quantity. SIMILITUDE, in arithmetic, geometry, X |