Part 1

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ENCYCLOPAEDIA BRITANNICA

A DICTIONARY OF ARTS, SCIENCES, LITERATURE AND GENERAL INFORMATION

ELEVENTH EDITION

VOLUME V, SLICE VI

Celtes, Konrad to Ceramics

ARTICLES IN THIS SLICE:

CELTES, KONRAD CENTO (town of Italy) CELTIBERIA CENTO (composition) CEMENT CENTRAL AMERICA CEMETERY CENTRAL FALLS CENCI, BEATRICE CENTRALIA CENOBITES CENTRAL INDIA CENOMANI CENTRAL PROVINCES AND BERAR CENOTAPH CENTUMVIRI CENSOR CENTURION CENSORINUS CENTURIPE CENSUS CENTURY CENTAUREA CEOS CENTAURS CEPHALIC INDEX CENTAURUS CEPHALONIA CENTAURY CEPHALOPODA CENTENARY CEPHEUS CENTERVILLE CEPHISODOTUS CENTIPEDE CERAM CENTLIVRE, SUSANNA CERAMICS

CELTES, KONRAD (1459-1508), German humanist and Latin poet, the son of a vintner named Pickel (of which Celtes is the Greek translation), was born at Wipfeld near Schweinfurt. He early ran away from home to avoid being set to his father's trade, and at Heidelberg was lucky enough to find a generous patron in Johann von Dalberg and a teacher in Agricola. After the death of the latter (1485) Celtes led the wandering life of a scholar of the Renaissance, visiting most of the countries of the continent, teaching in various universities, and everywhere establishing learned societies on the model of the academy of Pomponius Laetus at Rome. Among these was the _Sodalitas litteraria Rhenana_ or _Celtica_ at Mainz (1491). In 1486 he published his first book, _Ars versificandi et carminum_, which created an immense sensation and gained him the honour of being crowned as the first poet laureate of Germany, the ceremony being performed by the emperor Frederick III. at the diet of Nuremberg in 1487. In 1497 he was appointed by the emperor Maximilian I. professor of poetry and rhetoric at Vienna, and in 1502 was made head of the new Collegium Poetarum et Mathematicorum, with the right of conferring the laureateship. He did much to introduce system into the methods of teaching, to purify the Latin of learned intercourse, and to further the study of the classics, especially the Greek. But he was more than a mere classicist of the Renaissance. He was keenly interested in history and topography, especially in that of his native country. It was he who first unearthed (in the convent of St Emmeran at Regensburg) the remarkable Latin poems of the nun Hrosvitha of Gandersheim, of which he published an edition (Nuremberg, 1501), the historical poem _Ligurinus sive de rebus gestis Frederici primi imperatoris libri x._ (Augsburg, 1507), and the celebrated map of the Roman empire known as the _Tabula Peutingeriana_ (after Konrad Peutinger, to whom he left it). He projected a great work on Germany; but of this only the _Germania generalis_ and an historical work in prose, _De origine, situ, moribus et institutis Nurimbergae libettus_, saw the light. As a writer of Latin verse Celtes far surpassed any of his predecessors. He composed odes, elegies, epigrams, dramatic pieces and an unfinished epic, the _Theodoriceis_. His epigrams, edited by Hartfelder, were published at Berlin in 1881. His editions of the classics are now, of course, out of date. He died at Vienna on the 4th of February 1508.

For a full list of Celtes's works see Engelbert Klüpfel, _De vita et scriptis Conradi Celtis_ (2 vols., Freiburg, 1827); also Johann Aschbach, _Die früheren Wanderjahre des Conrad Celtes_ (Vienna, 1869); Hartmann, _Konrad Celtes in Nürnberg _(Nuremberg, 1889).

CELTIBERIA, a term used by Greek and Roman writers to denote, sometimes the whole north-east of Spain, and sometimes the north-east part of the central plateau of the peninsula. The latter was probably the correct use. The Celtiberi, in this narrower sense, were not so much one tribe as a group of cantons--Arevaci, Pelendones, Berones and four or five others. They were the most warlike people in Spain, and for a long time offered a stubborn resistance to the Romans. Originally Carthaginian mercenaries, they were induced to serve the Romans in a similar capacity, and Livy (xxiv. 49) distinctly states that they were the first mercenaries in the Roman army. They did not, however, keep faith, and several campaigns were undertaken against them. In 179 B.C. the whole country was subdued by T. Sempronius Gracchus, who by his generous treatment of the vanquished gained their esteem and affection. In 153 they again revolted, and were not finally overcome until the capture of Numantia (133). The twenty years' war waged round this city, and its siege and destruction by Scipio the Younger (133 B.C.) form only the most famous episode in the long struggle, which has left its mark in entrenchments near Numantia excavated in 1906-1907 by German archaeologists. After the fall of Numantia, and still more after the death of Sertorius (72 B.C.), the Celtiberians became gradually romanized, and town life grew up among their valleys; Clunia, for instance, became a Roman municipality, and ruins of its walls, gates and theatre testify to its civilization; while Bilbilis (Bambola), another municipality, was the birthplace of the eminently Roman poet Martial. The Celtiberians may have been so called because they were thought to be the descendants of Celtic immigrants from Gaul into Iberia (Spain), or because they were regarded (cf. Lucan iv. 9) as a mixed race of Celts and Spaniards (Iberians); in either case the name represents a geographer's theory rather than an ascertained fact. That a strong Celtic element existed in Spain is proved both by numerous traditions and by the more trustworthy evidence of place-names. The Celtic place-names of Spain, however, are not confined to Celtiberia or even to the north and east; they occur even in the south and west.

A long description of the manners and customs of the Celtiberi is given by Diodorus Siculus (v. 33, 34). Their country was rough and unfruitful as a whole (barley, however, was cultivated), being chiefly used for the pasture of sheep. Its inhabitants either led a nomadic life or occupied small villages; large towns were few. Their infantry and cavalry were both excellent. In battle, they adopted the wedge-shaped formation of the column. They carried double-edged swords and short daggers for use hand to hand, the steel of which was hardened by being buried underground; their defensive armour was a light Gallic shield or a round wicker buckler, and greaves of felt round their legs. They wore brazen helmets with purple crests, and rough-haired black cloaks, in which they slept on the bare ground. Like the Cantabri, they washed themselves with urine instead of water. They were said to offer sacrifice to a nameless god (Strabo iii. p. 164) at the time of the full moon when all the household danced together before the doors of the houses. Although cruel to their enemies, they were hospitable to strangers. They ate meat of all kinds, and drank a kind of mead. E. Hübner's article in Pauly-Wissowa's _Realencyclopadie_, iii. (1886-1893), collects all the ancient references, which are almost all brief. Strabo's notice (bk. iii.), based perhaps on Poseidonius, is fullest. (F. J. H.)

CEMENT (from Lat. _caementum_, rough pieces of stone, a shortened form of _caedimentum_, from _caedere_, to cut), apparently first used of a mixture of broken stone, tiles, &c., with some binding material, and hence of any material capable of adhering to, and uniting into a coherent mass, fragments of a substance not in itself adhesive. The term is often applied to adhesive mixtures employed to unite objects or parts of objects (see below), but in engineering, when used without qualification, it means Portland cement, its modifications and congeners; these are all hydraulic cements, i.e. when set they resist the action of water, and can, under favourable conditions, be allowed to set under water.

_Hydraulic Cements_.--It was well known to builders in the earliest historic times that certain limes would, when set, resist the action of water, i.e. were hydraulic; it was also known that this property could be conferred on ordinary lime by admixture of silicious materials such as pozzuolana or tufa. We have here the two classes into which hydraulic cements are divided.

Pozzuolanic cement.

When pure chalk or limestone is "burned," i.e. heated in a kiln until its carbonic acid has been driven off, it yields pure lime. This slakes violently with water, giving slaked lime, which can be made into a smooth paste with water and mixed with sand to form common mortar. The setting of the mortar is due to the drying of the lime (a purely physical phenomenon, no chemical action occurring between the lime and the sand). The function of the sand is simply that of a diluent to prevent undue shrinkage and cracking in drying. Subsequent hardening of the mortar is caused by the gradual absorption of carbonic acid from the air by the lime, a skin of carbonate of lime being formed; but the action is superficial. Mortar made from pure or "fat" lime cannot withstand the action of water, and is only used for work done above water-level. If, however, such "fat" lime is mixed in the presence of water, not with sand but with silica in an active form, i.e. amorphous and (generally) hydrated, or with a silicate containing silica in an active condition, it will unite with the silica and form a silicate of lime capable of resisting the action of water. The mixture of the lime and active silica or silicate is a pozzuolanic cement. The simplest of all pozzuolanic cements would be a mixture of pure lime and hydrated silica, but though the latter is prepared artificially for various purposes, it is too expensive to be used as a cement material. A similar obstacle lies in the way of using a certain native form of active silica, viz. kieselguhr, for it is too valuable as an absorbent of nitroglycerine, for the manufacture of dynamite, to be available for making pozzuolanic cement. There are, however, many silicious substances occurring abundantly in nature which can thus be used. They are mostly of volcanic origin, and include pumice, tufa, santorin earth, trass and pozzuolana itself. The following analyses show their general composition:--

+-----------------------------+-----------+-----------+-----------+ | |Neapolitan | Roman | | | | Pozzuo- | Pozzuo- | Trass | | | lana | lana |(per cent) | | |(per cent) |(per cent) | | +-----------------------------+-----------+-----------+-----------| | Soluble silica (SiO2) | 27.80 | 32.64 | 19.32 | | Insoluble silicious residue | 35.38 | 25.94 | 50.40 | | Alumina (Al2O3) | / 19.80 | / 22.74 | 13.86 | | Ferric oxide (Fe2O3) | \ | \ | 3.10 | | Lime (CaO) | 5.68 | 4.06 | · · | | Magnesia (MgO) | 0.35 | 1.37 | 0.13 | | Sulphuric anhydride (SO3) | Trace | Trace | · · | | Combined water (H2O) | / 4.27 | / 8.92 | 7.57 | | Carbonic anhydride (CO2) | \ | \ | · · | | Moisture | · · | · · | 5.04 | | Alkalis and loss | 6.72 | 4.33 | 0.58 | | +-----------+-----------+-----------+ | | 100.00 | 100.00 | 100.0 | +-----------------------------+-----------+-----------+-----------+

An artificial product which serves perfectly as a pozzuolana is granulated blast-furnace slag. The slag, which must contain a high percentage of lime, is granulated by being run while fused into abundance of water. This granulated slag differs from the same slag allowed to cool slowly, in that a portion of the energy which it possesses while fused is retained after it has solidified. It bears to ordinary slowly-cooled slag a similar relation to that borne by plastic sulphur to ordinary crystalline sulphur. This potential energy becomes kinetic when the slag is brought into contact with lime in the presence of water, and causes the formation of a true hydraulic silicate of lime. The following analysis shows the composition of a typical slag:--

Per Cent. Insoluble residue 1.04 Silica (SiO2) 31.50 Alumina (Al2O3) 18.56 Manganous oxide (MnO) 0.44 Lime (CaO) 42.22 Magnesia (MgO) 3.18 Soda (Na2O) 0.70 Sulphuric anhydride (SO3) 0.45 Sulphur (S) 2.21 ------ 100.30 Deduct oxygen equivalent to sulphur 1.10 ------ 99.20

Granulated slag of this character is ground with slaked lime until both materials are in a state of fine division and intimately mixed. The usual proportions are three of slag to one of slaked lime by weight. The product termed slag cement sets slowly, but ultimately attains a strength scarcely inferior to that of Portland cement. Although it is cheap and suitable for many purposes, its use is not large and tends to decrease. Pozzuolanic cements are little used in England. Generally speaking, they are only of local importance, their cheapness depending largely on the nearness and abundance of some suitable volcanic deposit of the trass or tufa class. They are not usually manufactured by the careful grinding together of the pozzuolana and the lime, but are mixed roughly, a great excess of pozzuolana being employed. This excess does no harm, for that part which fails to unite with the lime serves as a diluent, much as does sand in mortar. In fact, ordinary pozzuolanic cement made on the spot where it is to be used may be regarded as a better kind of common mortar having hydraulic qualities. Good hydraulic mortars may be made from lime mixed with furnace ashes or burnt clay as the pozzuolanic constituent.

Portland Cement

Cements of the Portland type differ in kind from those of the pozzuolanic class; they are not mechanical mixtures of lime and active silica ready to unite under suitable conditions, but consist of definite chemical compounds of lime and silica and lime and alumina, which, when mixed with water, combine therewith, forming crystalline substances of great mechanical strength, and capable of adhering firmly to clean inert material, such as stone and sand. They are made by heating to a high temperature an intimate mixture of a calcareous substance and an argillaceous substance. The commonest of such substances in England are chalk and clay, but where local conditions demand it, limestone, marl, shale, slag or any similar material may be used, provided that the correct proportions of lime, silica and alumina are maintained. The earliest forms of cements of the Portland class were the hydraulic limes. These are still largely used, and are prepared by burning limestones containing clayey matter. Some of these naturally possess a composition differing but little from that of the mixture of raw materials artificially prepared for the manufacture of Portland cement itself. Although hydraulic limes have been in use from the most ancient times, their true nature and the reason of their resistance to water have only become known since 1791. Next in antiquity to hydraulic lime is Roman cement, prepared by heating an indurated marl occurring naturally in nodules. Its name must not be taken to imply that it was used by the ancients; in point of fact the manufacture of this substance dates back only to 1796.

With the growth of engineering in the early part of the 19th century arose a great demand for hydraulic cement. The supply of materials containing naturally suitable proportions of calcium carbonate and clay being limited, attempts were made to produce artificial mixtures which would serve a similar end. Among those who experimented in this direction was Joseph Aspdin, of Leeds, who added clay to finely ground limestone, calcined the mixture, and ground the product, which he called Portland cement. The only connexion between Portland cement and the place Portland is that the cement when set somewhat resembles Portland stone in colour. True, it is possible to manufacture Portland cement from Portland stone (after adding a suitable quantity of clay), but this is merely because Portland stone is substantially carbonate of lime; any other limestone would serve equally well. Although Portland cement is later in date than either Roman cement or hydraulic lime, yet on account of its greater industrial importance, and of the fact that, being an artificial product, it is of approximately uniform composition and properties, it may conveniently be treated of first. The greater part of the Portland cement made in England is manufactured on the Thames and Medway. The materials are chalk and Medway mud; in a few works the latter is replaced by gault.

The composition of typical samples of chalk and clay is shown in the following analyses:--

+-----------------------------------+----------------------------------------------------------------------------+ | Chalk. | Clay. | +-------------------------+---------+----------------------------+---------+------------------+-------+----------+ | |Per cent.| |Per cent.| | | | |Silica (SiO2) | 0.92 | Insoluble silicious matter | 26.67 |Consisting of | | | |Alumina+ferric oxide | | Silica (SiO2) | 31.24 | Quartz (SiO2) | 19.33 | | | (Al2O2 + Fe2O3) | 0.24 | Alumina (Al2O3) | 16.60 | Silica (SiO2) | 5.19 |\ | |Lime (CaO) | 55.00 | Ferric Oxide (Fe2O3) | 8.66 | Alumina (Al2O3) | 1.47 | >Feldspar| |Magnesia (MgO) | 0.36 | Lime (CaO) | 0.25 | Magnesia (MgO) | 0.03 | | 7.34% | |Carbonic anhydride (CO2) | 43.40 | Magnesia (MgO) | 1.91 | Soda (Na20) | 0.65 |/ | | | ----- | Soda (Na2O) | 1.00 | | ----- | | | | 99.92 | Potash (K2O) | 0.45 | | 26.67 | | | | | Sodium Chloride (NaCl) | 1.86 | | | | | | | Combined water, organic | | | | | | | | matter, and loss | 11.36 | | | | | | | | ------ | | | | | | | | 100.00 | | | | +-------------------------+---------+----------------------------+---------+------------------+-------+----------+

Mixing.

Loading the kiln.

[Illustration: FIG. 1]

These materials are mixed in the proportion of about 3:1 by weight so that the dried mixture contains approximately 75% of calcium carbonate, the balance being clay. The mixing may be effected in several ways. The method once exclusively used consists in mixing the raw materials with a large quantity of water in a wash mill, a machine having radial horizontal arms driven from a central vertical spindle and carrying harrows which stir up and intermix any soft material placed in the pit in which the apparatus revolves. The raw materials in the correct proportion are fed into this mill together with a large quantity of water. The thin watery "slip" or slurry flows into large settling tanks ("backs") where the solids in suspension are deposited; the water is drawn off, leaving behind an intimate mixture of chalk and clay in the form of a wet paste. This is dug out, and after being dried on floors heated by flues is ready for burning. This process is now almost obsolete. According to present practice the raw materials are mixed in a wash mill with so much water that the resulting slurry contains 40 to 50% of water. The slurry, which is wet enough to flow, is ground between millstones so as to complete the process of comminution begun in the wash mill. Thorough grinding and mixing are of the utmost importance, as otherwise the cement ultimately produced will be unsound and of inferior quality. The drying of the slurry is generally effected by the waste heat of the kilns, so that while one charge is burning another is drying ready for the next loading of the kilns. The kilns commonly employed are "chamber kilns," circular structures not unlike an ordinary running lime kiln, but having the top closed and connected at the side with a wide flue in which the slurry is exposed to the hot products of combustion from the kiln. The farther ends of the flues of several such kilns are connected with a chimney shaft. The slurry, in drying on the floor of the flue, forms a fairly tough cake which cracks spontaneously in the process of drying into rough blocks suitable for loading into the kiln. At the bottom of the kiln is a grate of iron bars, and on this wood and coke are piled to start the fire. A layer of dried slurry is loaded on this, then a layer of coke, then a layer of slurry, and so on until the kiln is filled with coke and slurry evenly distributed. Fresh slurry is run on to the drying floors, and the kiln is started. The construction of an ordinary chamber kiln may be gathered from the accompanying diagram (fig. l). The operation of burning is a slow one. An ordinary kiln, which will contain about 50 tons of slurry and 12 tons of coke, will take two days to get fairly alight, and will be another two or three days in burning out. Therefore, allowing adequate time for loading and unloading, each kiln will require about one week for a complete run. The output will be about 30 tons of "clinker" ready to be ground into cement. The grinding of the hard rock-like masses of clinker is effected between millstones, or in modern plants in ball-mills, tube-mills and edge-runners. It is an important part of the manufacture, because the finished cement should be as fine and "floury" as possible. The foregoing description represents the procedure in use in many English factories. There are various modifications in practice according to local conditions: a few of these may be described. In all cases, however, the main operations are the same, viz. intimately mixing the raw materials, drying the mixture, if necessary, and burning it at a clinkering temperature (about 1500° C. =2732° F.). Thus when hard limestone is the form of calcium carbonate locally available, it is ground dry and mixed with the correct proportion of clay also dried and ground. The mixture is slightly damped, moulded into rough bricks, dried and burned. A possible alternative is to burn the limestone first and mix the resulting lime with clay, the mixture being burned as before. By this method grinding the hard limestone is avoided, but there is an extra expenditure of fuel in the double burning.

Other kilns.