Silique

suspensions of galvanometers; in the use of blown quartz flasks, tubes, thermometers for special purposes; while its transparency to ultra-violet light, and the polarizing properties of the crystals, render it invaluable for optical uses. Its resistance to wear and atmospheric influence also makes it useful for ornamental purposes, for standard weights, and for mortars for grinding minerals. As prepared artificially silica is an amorphous white solid, the product obtained by the reactions in aqueous solutions being united with water to form a silicic acid of undetermined constitution. If prepared by the reaction of dilute solutions of sodium silicate and hydrochloric acid, the silicic acid remains dissolved, the solution being separable from the salt and excess of acid by dialysis. On evaporation of the solution a glassy mass results, that does not redissolve; but the solution, which does not affect litmus, and shows no marked chemical properties, soon sets to a jelly.

Silique, the fruit of certain cruciferous plants, consisting of

Silique.

a pair of valves which separate from a central septum. (anc. Durostorum),

Silistria tn., Bulgaria, cap. of co. of same name, on r. bk. of Danube, 72 m. N.W. of Varna; an important trade centre, with cloth manufactories and distilleries. It was ceded to Bulgaria in 1878. Pop. (1901) 12,133.

Silius (c. 25 to 100 A.D.), Italian poet, whose full name was Gaius Silius Italicus, won distinction as an advocate, and became a member of the judicial board of the centumviri; in 68 (Nero's last year) he was made consul, and afterwards governed the province

of Asia. The latter years of his life he passed in studious retire

217

ment, either at Puteoli or in the house known as Virgil's, near Naples. He starved himself to death because of the pain caused by an incurable disease. He wrote a dull epic poem Punica, on the chief events of the second Punic War. Edited by Bauer (1890-2); Eng. verse trans. by Ross (1672).

Siljan, one of the most picturesque lakes of Central Sweden, formed by the Dal R., is known as the 'eye' of Dalecarlia.

Silk, the most beautiful of textile materials, is the produce of the silkworm, which yields it as a finished thread, so that, strictly speaking, no spinning is required. Under the microscope silk shows like a glass rod, and the play of light along its unbroken surface is the cause of its splendid lustre. The silk fibre is exceedingly strong, and is composed of a core of fibroin, resembling horn, and coated with a gelatinous substance (sericin) of somewhat similar composition. Silk originally came to Europe from China, whence the culture spread also into Japan and India; and these two countries are now also large producers, Japan in particular having of late invaded the Western markets and secured a good position for her woven goods. In Europe the cultivation of the silkworm was introduced about the 16th century, and settled in the countries round the Mediterranean, the climate being suitable for the mulberry tree, which is the natural food of Bombyx mori, the moth that is commercially most valuable for producing silk. Italy produces the largest quantity, Syria and France follow; but the whole Western production of silk is not one-third of the European consumption. Attempts have been made to introduce the culture of the silkworm into the United States and Australia, but with little success, as it is a business which requires a large supply of careful and cheap labor, and only for a short period in the year. In reeling alone can any aid be had from machinery. In Asia some species of the silkworm are bivoltine, and some even multivoltine; but in Europe the Bombyx mori produces only one crop per year. The eggs, of which the female deposits about five hundred, are laid in August or September, and hatched the following May, when the mulberry comes into leaf. The hatching and feeding are conducted indoors, and in some districts this is a cottage industry. The egg when hatched produces a small caterpillar, which feeds voraciously for more than a month, until it grows to about three inches in length. The worms

Silk

then begin to sicken and cast their skins, and in a day or two commence again with renewed appetite. This happens four times. At the end of about a month the worm finally ceases to eat, mounts up on the twigs which are placed on its tray, and begins to spin its cocoon. Out of two little openings in its head, called 'spinnerets,' proceed two slender filaments of the glutinous substance from which the silk is derived. These stick side by side and form a flat thread, which the silkworm, by moving about its head, folds around its body, like a ball of thread, wrapped from the outside inwards, till it has completely embedded itself in this silky covering, where it rests in the pupa state. If left to itself the insect would in two or three weeks be ready to emerge, and would bore its way out at the end of the cocoon, and appear as a small ashy-white, feeble moth. The pairing takes place at once, the eggs are laid, and within a week the cycle of life is complete. But as the exit of the moth from the cocoon cuts the fibres across, and so destroys the most valuable part of the silk, only so many insects as may be necessary for producing sufficient eggs for next year's crop are allowed to emerge; the others are stifled by being placed in a heated oven.

The next process is to wind as much as possible off the cocoons into hanks. In Europe and in some Oriental towns this is done with improved machinery in factories called filatures. It is usually begun when the cocoons are fresh. Each operator has before her a basin of hot water, the temperature of which is regulated by a steam-pipe or a fire, and overhead is a reel turning slowly. After removing the outside flossy covering, the girl places the cocoons in the basin, with the result that the hot water softens the natural gum that is in the silk, and allows it to be wound off. The filaments are passed through several glass eyes, and crossed, and thus become glued together into a thread which is called 'singles,' and when further prepared is known as 'thrown silk.' The singles are reeled into large hanks called 'knots,' each bunch of hanks being called a moss," and each bundle a 'book.' In this form Asiatic silk is imported into Europe and the U. S. The quantity of such silk obtained from one cocoon is very smallseldom up to a thousand yards, generally not more than five hundred yards. The remainder of the cocoon is either too flossy or too entangled to be wound. This waste portion forms the material from which spun silk is prepared. The further preparation of

6

thrown silk for the weaver merely consists in cleaning, assorting, and doubling to the necessary thickness, and twisting to give the strength desired. The singles are frequently used for warps for light fabrics, and although some of this silk is so fine as to have five hundred thousand yards of length in one pound weight (technically known as '9 denier silk'), it is quite strong enough to be woven in a powerloom. For the warp of heavier fabrics organzine' is required. This is made by the singles being twisted the one way on the single thread, and then two or more

seded by combing, carried out as with wool. All such materials go through three distinct processes, the fibres being straightened, equalized, and twisted. The straightening is done by steel combs, which remove impurities, lay the fibres all one way, and deliver them in the form of a ribbon or sliver.' Groups of slivers are thereafter run together again and again, and drawn out, till at length an equalized and level thread is produced. This is finally twisted to the required degree, but the product is inferior in lustre to thrown silk. Silk fabrics are produced by similar

carried to great lengths: for example, the Lyons silk-dyers can load a Schappe spun silk (cordonnet) in black up to 900 per cent., but usually do it to 400 per cent.; which means that 100 lbs. of silk, when dyed, will weigh 500 lbs. Although the weighting of silk is defended on the ground that it is merely a method of giving a firm finish, there is always present an element of deception, and the durability of the fabric is much impaired.

Besides the mulberry-feeding silkworm there are other species which feed on different plants, and yield what are usually spoken

threads twisted the opposite way on the double or plied threadthus giving strength and elasticity. Tram' for weft has no twist on the single thread, and only a slight twist on the double or plied thread. In the same way heavier threads for sewings, embroideries, and fringes are made from the singles by doubling up the requisite number of strands.

At first spun silk was carded like woollen yarn-a method adapted to produce felting, but to injure lustre. This class is still made, and is called 'short spun silk'; but more recently the process has been super

methods of weaving as other textiles, though special contrivances have been devised to handle such delicate threads, and to economize a material so valuable.

In the manufacture of silk textiles dyeing and finishing are most important operations. Thrown silk, before being dyed, is boiled in a strong solution of fine white soap, to extract the natural gum. Thereafter it takes on the most brilliant tints, but loses in weight from 25 to 30 per cent. fringes and tassels this lightness is objectionable, and doubtless it was to make fringes hang properly that the weighting of silk was first introduced. It has been

For

of as wild silks. But, strictly speaking, there are no wild silks; all cocoons that are of commercial value are cultivated. The most important of this class is the tussur worm (Antheroa Pernyi), which is an oak feeder, and is produced largely in China: a similar species is also cultivated in India. The cocoon gives off a coarse filament, which is flat like a ribbon, and causes the silk to have a peculiarly glittering appearance. It is of a yellowishbrown color, which cannot be discharged by boiling; but it dyes well, though requiring special treatment by stretching and steaming to bring up the lustre.

Silk

The natural tint is pleasing and durable, and undyed tussur cloths are not only much worn in the East, but are largely imported into the United States and Europe. The only others of the so-called wild silks which are of any commercial value are eria (Attacus Ricini) and muga (Antheræa assama); but they cannot be reeled to a profit, and only serve for spun silk.

ARTIFICIAL SILK is made from cellulose, obtained either from wood pulp or from specially prepared cotton. The manufacture involves three main processes: (1) The cellulose solution, being forced under high pressure through glass tubes or steel plates provided with capillary openings, emerges in the form of filaments. (2) These filaments are passed through various precipitating solutions to cause them to coagulate and, where necessary, render them non-inflammable. The filaments, thus prepared, are spun into threads.

(3)

Artificial silk readily takes brilliant dyes, and the filaments can be moulded into any desired shape. It is made into fabrics, ribbons, braid, and imitation straw, grass, and horse hair. On the other hand, it is sensitive to treatment with soap, alkalies, and bleaches; and when wet is not as strong as the natural product, because the cellulose tends to return to the jelly state in the presence of water. On account of these drawbacks there has been little competition with the natural silk industry; but so decided is the improvement of the last fifteen years in the strength of the artificial fabric, and so active is experimentation to that end, that strong competition is no remote possibility.

with

The following varieties of artificial silk are now on the market: Chardonnet artificial silk is prepared by treating cotton nitric acid, and dissolving the resulting nitro-cellulose in a mixture of alcohol and ether. The collodion jelly thus obtained is then forced through capillary tubes, and treated as already described. The annual production is about 2,000,000 kilos (4,400,000 lbs.).

Cupro-Ammonium Silk is made by dissolving cellulose in a solution of copper hydroxide in ammonia water, which is pressed into threads that take on a glossy appearance. The annual production is about

3,190,000 lbs.

are made

Viscose Silk (cellulose xanthogenate). Wood-pulp is treated with caustic soda and carbon disulphide, and the solution pressed into threads which glossy (mercerized) by stretching and treating with caustic soda. This mercerization is also applicable to cotton goods. Production is about 1,320,000 lbs.

Acetyl Cellulose is prepared by the action of acetyl chloride on

219

cotton, dissolving in chloroform, and moulding. This product is also formed into sheets, like celluloid, and called Cellit, which is especially adapted for moving-picture films, as it is non-inflammable. Cellit is also used as a waterproof covering for paper, leather, cloth, wood, etc.

Consult Butler's Silkworms (1892); Posselt's Structure of Fibres, Yarns, and Fabric (1890); Vignon's La Soie (1890); E. Pariset's Les Industries de la Soie (1890); De l'Arbousset's On Silk and the Silkworm (1905); Chaplet and Rousset's Succédanés de la Soie (1908); Herzog's Unterscheidung der Natürlichen und Künstlichen Seiden (1910).

Silk Cotton, the fibre which fills the interstices between the seeds in the large, woody capsules of certain tropical trees belonging to the order of Malvacea. The fibre is too short to be used ex

cept for packing purposes. It is extensively utilized in stuffing pillows, cushions, mattresses, and the like. Among the trees from which silk cotton is obtained are Ochroma lagopos, Eriodendron anfractuosum, and Bombax malabaricum.

Silkworm. See SILK.

Silkworm Gut, a strong material used by anglers for dressing the hook ends of fishing-lines, and prepared from the caterpillars of the ordinary silkworm. The worms, when about to spin their cocoons, are immersed in vinegar for a time, and afterward pulled asunder. A long, glutinous thread is then formed by the silky secretion of the caterpillar. These threads are stretched on a board, and allowed to dry in the sun. It is mostly prepared

in Spain and Italy, though some exports are still made from China.

Sill, EDWARD ROWLAND (1841

87), American essayist, and

educator, was

at Windsor,

Conn. He graduated at Yale in 1861, then passed several years in California on account of poor health, and in 1866 studied divinity at Harvard. He was occupied as a teacher and with literary work in New York and Ohio until 1871, when he became principal of the Oakland, Cal., high school. From 1874 to 1882 he was professor of English literature at the University of California, afterward residing at Cuyahoga Falls, N. Y. His lyrics are marked by melody and insight. He published Hermione, and Other Poems (1867), and The Hermitage, and Later Poems (1867). Posthumous volumes are Venus of Milo, and Other Poems (1888), Prose of Edward Rowland Sill (1900), Complete Poems (1906). See Downey's Life (1906); Mrs. PhelpsWard's Chapters from a Life (1897).

Sill, JOSHUA WOODROW (183162), American soldier, was born at

Silliman

Chillicothe, O. He graduated at the U. S. Military Academy in 1853; was an instructor at that institution during 1854-57. In April, 1861, he was appointed assistant adju tant-general of Ohio; was promoted colonel in August, 1861, and brigadier-general in July, 1862; fought at Rich Mountain and Perryville; and in the Battle of Stone River was killed while gallantly endeavoring to rally his brigade.

Silliman, BENJAMIN (17791864), American scientist, was born in North Stratford, now Trumbull, Conn. His father, Gold Selleck Silliman, held the rank of a brigadier-general in the Connecticut militia during the Revolutionary War. Benjamin graduated in the class of 1796 at Yale College. Soon after his graduation, he was invited to a professorship of chemistry and natural history in Yale College. He accepted the call, and fitted himself for his duties by studies in Philadelphia and in Edinburgh. He returned to New Haven, and entered upon his lifework in the summer of 1806. For more than half a century he was a popular lecturer. He gave the first course of lectures before the Lowell Institute in Boston; and was called to many other cities, where his brilliant experiments, striking diagrams, and clear and pleasant presentation of scientific themes rendered him a most popular lecturer. He was the college representative before the public, and secured many important donations, including the Clark telescope, the collection of minerals made by Col. George Gibbs, and the Trumbull Gallery of paintings. He was also influential in promoting the geological survey of Connecticut. In the organization of the Medical School at Yale College he was particularly active, and his influence in the foundation of the Sheffield School was noteworthy. His contributions to the progress of science were chiefly indirect. He inspired a great many who became teachers and investigators; but his influence was chiefly exerted in the establishment and n.a'ntenance of the American Journal of Science, which from the time of its commencement in 1818 has remained in the charge of successive members of his family. For twenty years he was the sole editor, and for eight years more the senior editor of that journal. Silliman is remembered by the volumes which he wrote upon his travels in Europe and in this country. See Fisher's Memoir (2 vols., 1865).

He

Silliman, BENJAMIN, JR. (181685), American chemist, was born in New Haven, Conn., the son of Benjamin Silliman (q.v.). was graduated at Yale in 1837. In 1837-46 he was an assistant in chemistry; in 1846-53, professor of applied chemistry; and in 1853

85 professor of chemistry in Yale. In 1844 he built a private chemical laboratory in which he carried out many valuable experiments with the assistance of Yale students, and the results of this work in influencing the students to carry out original research determined the Yale faculty to accede to Silliman's requests for a similar laboratory for the university. In 1846 the School of Applied Chemistry was established and was so successful that in 1847 it was enlarged and re-named the Yale Scientific School. In 1845-46 Silliman visited New Orleans and delivered the first public lectures in the United States on agricultural chemistry. In 1849-54 he was professor of medical chemistry and toxicology in the University of Louisville, Ky., and in 1853 he had charge of the depart ments of mineralogy and geology in the World's Fair, New York. He was editor of the American Journal of Science in 1845-85, and in conjunction with Charles R. Goodrich edited World of Science, Art and Industry (1853), and Progress of Science and Mechanism (1854). He was author of: First Principles of Chemistry (1846); Principles of Physics (1858); and American Contributions to Chemistry (1875).

Sillimanite, a fibrous silicate of aluminium, AlSiO5, with a composition similar to that of cyanite. It is found in certain gneisses and schists.

Silo. A specially-constructed building for storing ensilage. Originally a pit in the earth, the silo is now a surface structure of any convenient form and depth, strongly built and air-tight. It is generally constructed of wood, but various other materials are used. Ensilage could be preserved in the open air, the outer surface decaying and forming an air-tight covering for the green fodder within, but this would be highly wasteful. The circular form of silo is more expensive to construct, but it is more convenient and economical in use because it permits uniform packing and settling and prevents the waste caused by loosely packed corners. Square silos should have their corners boarded across. The inside sheathing should run perpendicular to the bottom, and where stone, brick, or cement is used the inside walls should have a smooth dressing of Portland cement. The size should depend on the number of animals to be fed, calculating a cubic foot of ensilage to weigh 35 to 40 pounds, which is about the daily ration of a dairy cow weighing 1,000 pounds. cow will, therefore, consume 180 cubic feet of ensilage, or about 3 tons during a period of six

One

months. No account is made in this calculation for spoiled ensilage and waste, and a liberal allowance should be made for this. A circular silo 14 feet in diameter and 30 feet deep will hold 90 tons of ensilage, and a silo 15 feet square and 20 feet deep will hold 94 tons.

Siloam, or SHILOAH, a rock-cut pool or reservoir at the s. wall of Jerusalem, near the mouth of the Tyropcon valley (now Birket Silwan). The tower of Siloam (Luke 13: 4) may have been part of the wall near the pool. Its waters were believed to have healing properties (John 9:7). The Siloam inscription, discovered 1880, was cut on the rock of a conduit, leading from the Virgin's Spring, 500 yards to the north, to the Pool of Siloam. It records the construction of the conduit, and is the oldest Hebrew inscription extant.

Siloam Springs, tn., Benton co., Ark., 27 m. s.w. of Bentonville, on the Kan. City S. R. R. It is the seat of Arkansas Conference College. Flour is milled. Pop. (1910) 2,405.

Silures, an ancient British people who inhabited S. Wales; they offered a stubborn resistance to the Romans and to the English. From them the name Silurian has been given to the geological formation so called.

Silurian, in geology, a general name for those rocks which are post-Cambrian and pre-Devonian. Many writers recognize two systems as occupying this intervala lower or Ordovician (see ORDOVICIAN), and an upper or Silurian; but others prefer the terms Lower Silurian and Upper Silurian. The Silurian proper or Upper Silurian rocks consist mainly of conglomerates, sandstones, and shales, with a few important beds of limestone. The Silurian series as worked out in New York is the standard for America, having been first worked out in detail in that state. The subdivisions are: (3) Cayugan—

Manlius limestone.
Rondout waterlime.
Cobleskill limestone.
Salina beds.
(2) Niagaran-

Guelph dolomite.
Lockport limestone.
Rochester shale.
Clinton beds.

(1) Oswegan

Medina sandstone.
Oneida conglomerate.
Shawaugunk grit.

There is widespread unconformity between this series and the preceding Ordovician in America. The interval was one of mountain making, especially along the North Atlantic border. The Silurian strata are

most

heavily developed in the eastern part of the U. S. bordering the new mountain ranges. Important beds of waterlime used for the manufacture of natural cements occur; and the Clinton iron ores traced throughout the Appalachian belt and as far west as Wisconsin also belong in the Silurian.

In Europe the sequence of formations in the type district, the Welsh borders, as established by Murchison, are:

(3) Ludlow limestone, (2) Wenlock limestone, (1) Llandovery or Tarannon, corresponding closely to the three larger subdivisions in America.

The best-known areas of Silurian rocks on the Continent are those of Sweden, Bohemia, and Brittany. The limestones and shales of the island of Gothland have long been famous for the number and perfection of the fossils which they contain. Silurian rocks are also present in the W. Alps and in S. Russia. The number of fossils obtained from some of the limestones is enormous. In many respects the fauna is a continuation of that of the Ordovician. Fishes are characteristic of the highest Silurian strata. They belong to strange types, the affinities of which are not always clear, and include forms which are among the most interesting vertebrates known to science. The rise of the crinoids was a dominant feature, and the inauguration of reef building among corals is notable. Near the close of the period a remarkable

crustacean fauna, represented by Eurypterus and Pterogotus, was developed. There is evidence also of the existence of seaweeds, lycopods, and ferns. In most parts of the globe the Ordovician and Silurian rocks have been much folded, crushed, and compressed. The shales have often been converted into slates. Murchison's Siluria (ed. 1867) is of historical importance. Chamberlin and Salisbury, Geology, II. (1906).

Siluridæ. See CAT-FISH.

Silva, ANTONIO JOSÉ DA (170539), Portuguese dramatist, born at Rio de Janeiro; went to Lisbon, where he became one of the earliest writers of librettos for comic operas in Portugal. They were produced anonymously, all that was known of the author being that he was a Jew. His principal vaudevilles were Dom Quixote (1773), and the Esopaida. Silva was burned by the Inquisition. See David's Les Opéras du Juif (1880).

Silvanus, in ancient Latin mythology, the god of the fields and forests; he also watched over the boundaries of cultivated lands, and in particular over