897 



CELTIC ARCHITECTURE. 



CEMENT. 



693 



,-ibout the sources of the Duero and the Tagus, and both sides of the 

 great central ridge which divides the waters which flow east towards 

 the Mediterranean from those which flow west into the Duero and the 

 Tagus. The Celtiberi are spoken of by the Greek and Roman writers 

 sometimes as a single people, sometimes as a confederation of various 

 nations. In the latter sense they extended over a great part of central 

 Spain, including the Arevaci, Peleadones, Lusones, Belli, and Tisthi. 

 Appian places even the Vaccaji among the Celtiberi, but according to 

 Niebuhr they were pure Iberians. Numantia, in the country of the 

 Arevaci, is said by Florus to have been defended by 4000 Celtiberi. 

 The principal towns of the Celtiberi were Segobriga, not far from 

 Numantia, and different from the Segobriga, now Segorbe, near 

 Valentia , Turiaso, now Tarazona Bilbilis, the birth-place of Martial, 

 now Calatayud ; Argobriga, &c. The Celtiberi were a brave people, 

 superior, in firmness, to the Lusitani, who were chiefly pure Celts, and 

 they proved formidable both to the Carthaginians and the Romans. 

 After having submitted to Rome in the second Punic war, they 

 repeatedly resumed the contest, fought against Fulvius Flaccus, were 

 subjugated by T. Sempronius Gracchus 179 B.C., revolted a few years 

 after again under the pnetorship of Appius Claudius, and were again 

 defeated. They fought afterwards against C. Marcellus and Licinius 

 Lucullus. After the destruction of Numantia by Scipio ^milianus 

 they were finally subdued. Their country became part of the Roman 

 Provincia Tarraconensis. (Appian. ' De Rebus Hispan.'; Livy, &c ) 



CELTIC ARCHITECTURE. Under this term are classed the 

 structures, or collections of stones, which are usually considered to be 

 the work of the natives of our island anterior to the arrival of the 

 Romans. But very few, if any, of these structures have any claim to 

 be regarded as architectural works. The beginnings of architecture 

 are, however, undoubtedly perceptible in the series of stones, each 

 consisting of two uprights and an impost, which form so striking a 

 feature in the circles of Stonehenge : but they are only the beginnings. 

 The upright pillars have evidently undergone shaping ; and the mode 

 in which the imposts were secured by mortises and tenons, shows a 

 regular principle of construction. Something, also, of architectural 

 arrangement is exhibited in that very remarkable group of stones, and 

 in the far more extensive, but ruder series, at Avebury in Wiltshire 

 and Carnac in Brittany. But the ordinary stone circles and crom- 

 lechs of this and other countries are mere rude collections of unhewn 

 stones. 



The objects chiefly understood, when Celtic remains are spoken 

 of, are the stone circles mentioned above, cromlechs, kistvaens, and 

 upright stones, all of which are of the kind once generally, and still 

 vry frequently, termed Druidical; the circles being regarded as 

 Druidic temples, the cromlechs as Dniidic altars. Stonehenge, the 

 most perfect and the most finished of the stone-circles now remaining, 

 and Avebury, the most extensive relic of the kind left in this country, 

 will be found fully described (and the conjectures as to their purpose 

 examined) in the GEOGRAPHICAL DIVISION of the ENGLISH CYCLO- 

 PEDIA ; Stonehenge under WILTSHIRE, vol. iv., cols. 1139-41 ; AVEBURY 

 under that title, vol. i., cols. 743-6 ; and the great circle at Camac under 

 MOKBIIIAX, vol. iii., col. 863. CROMLECHS will be treated of under a 

 separate heading in the present Division ; and the small circles of stones 

 which formed the boundaries of barrows or tumuli, and kistvaens, 

 which are the stone chests or frames which were placed within the 

 barrows, will be spoken of under TUMULI ; and under those heads the 

 everal purposes they were intended to fulfil, and the state of civili- 

 Kition of which they are the evidence, will be most conveniently 

 examined. Here it will be enough to add, that whilst circles, upright 

 stones, and cromlechs are found very widely distributed throughout 

 Europe (and objects bearing a marked resemblance, if not a very 

 near affinity to them, are found in other parts of the world also), no 

 remains of any houses or buildings, properly so called, of the Celtic 

 period, have been discovered. The " Pen-pits " described by Sir 

 R. Colt Hoare, and by him called British Houses, can at best have only 

 been the foundations of houses of which the superstructures (which, if 

 we may trust Diodorus Siculus, were ordinarily among tfye Britons only 

 built of reeds or wood) have perished. 



CEMENT. At the present day the term cement is specifically 

 applied to those building materials used for the purpose of connecting 

 (small stones, or bricks, which set very rapidly ; and in this respect 

 cement differs from lime mortar, for the rate of setting of the latter is 

 ewentially slow and progressive. Cements themselves are subdivided 

 into the calcareoun, and the yt/figfout, and into the natural and artificial; 

 perhaps also a mixed class of iron, glass, oil, and bituminous cements 

 might be added to these, but their use is very limited. 



The natural calcareous cements are those obtained by the calcination 

 of the argillaceous limestones, in which the silicate of alumina is pre- 

 Mfiit in the proportions of from 30 to 60 per cent, of the whole mass, 

 though in the best materials of this description the proportion of the 

 silicate rarely attains even 50 per cent. It appears that after a stone 

 of thin description has been deprived of its carbonic acid gas, and itx 

 water of crystallisation, by the process of calcination, it is susceptible 

 uf forming, by the addition of water, a now hydrated double silicate of 

 lime and alumina, with very great rapidity ; and that the combination 

 o formed is of a very permanent character, and of great hardness and 

 tenacity. The degree of heat required for this calcination is moderate, 

 the fate of the natural cement*, and the etone loses in the kiln about 



one-third of its natural weight. It is then ground, and packed in as air- 

 tight a manner as possible in casks ; for the powder thus obtained has 

 a great affinity for moisture, and it absorbs readily that which may be 

 in suspension in the atmosphere. The cements made, and treated, in 

 this manner are usually known in commerce as the Roman cements, 

 and those -sold in England are obtained by the calcination of the 

 nodules of septaria dispersed in the liassic, the Oxford, or the tertiary 

 clays. Sinu'lar nodules are found in the clays of the oolitic series near 

 Boulogne, at Pouilly, Vassy, c., in France ; and in the United States 

 and Canada. As the composition of the nodules used in the manu- 

 facture of the English natural cements represents the normal type of 

 this class of materials, it is added : 



Carbonate of Lime 

 Silicate of alumina 



Sheppy. 

 per cent, 55 

 38 



Oxide of iron arid other substances 



Harwich. 



49 



47 



3 



Yorkshire. 



62 



34 



4 



The so-called Medina cement approaches very closely in its composition 

 to the Yorkshire, or Atkinson's cement. 



It is usually considered that the lighter the specific gravity of a 

 natural cement may be, the better will be its useful properties ; and 

 that the finer the powder into which it is ground, the more regular 

 will be its action. Upon the first addition of water, a certain amount 

 of heat will be evolved from the portion which enters into chemical 

 combination with the cement, and the operation of setting should not 

 be allowed to commence until the whole of this heat is given off. The 

 rate of setting will depend very much upon the quantity, and the 

 quality, of the water used, and upon the proportions of sand mixed 

 with the cement ; when pure cement, treated in the best manner, is 

 used, the setting will, in fact, take place within about six minutes ; 

 whereas if two proportions of sand be used to one of cement, and 

 much water be introduced, the time of setting may extend to as much 

 as one hour twenty minutes ; .and if the mortar so made be immersed 

 in sea water, the time of setting may even reach twenty-four hours. 

 It is considered that the average resistance of pure natural cements to 

 crushing weights, is equal to about 746 Ibs. per superficial inch; to an 

 effort of traction, their powers of resistance are only equal to 54 Ibs. 

 per superficial inch. 



Artificial cements are made either by mixing with the feebly 

 hydraulic limes natural substances, such as pozzuolano, or trass, which 

 are able to impart to them the power of setting iinder water ; or by 

 the addition of broken tiles, or underburnt clay, to those limes. Of 

 late years, however, both these systems of making artificial cemens 

 have been abandoned in England, and the use of what is called (rather 

 absurdly) the Portland cements has been substituted for them. These 

 Portland cements are obtained by burning together, under the influence 

 of intense heat, certain proportions of a soft and pure carbonate of 

 lime (such as the middle chalk around London) and the fine alluvial 

 mud of our English rivers ; the proportions of clay and carbonate of 

 lime being about, or rather less than, those of the Yorkshire cement 

 stones. 



The principal difference between the natural and the artificial cal- 

 careous cements, consists, it is to be observed, principally in the degree 

 of heat to which they are exposed ; and it would appear that the com- 

 binations effected under these circumstances have a very marked 

 influence upon the ultimate powers of resistance the cements attain. 

 The Portland cements, indeed, do not set so rapidly as do the Roman 

 cements, but when the setting has once commenced, the strength of 

 the resulting material continues to increase indefinitely ; whereas the 

 Roman cements soon attain a degree of strength which they do not 

 subsequently exceed even if they retain it. The resistance of Port- 

 land cement, of the best description, to efforts of compression, is esti- 

 mated to be equal to 2074 Ibs per superficial inch; and to efforts of 

 traction to 146 Ibs. per superficial inch. The time of setting is at least 

 from three to four times longer than that of the natural cements. 



In works of internal decoration the gypseous cements are largely 

 used ; and the rapidity with which they pass through the chemical 

 changes effected during their application, gives them a decided superi- 

 ority over the ordinary plasters. The materials of this description 

 most generally used are the Keene's, or the Parian cements; the 

 former of which is obtained by recalcining a dehydrised sulphate of 

 lime, which has been subsequently saturated with a solution of alum 

 and water ; the latter is obtained by recalcining, in the same way, a 

 plaster saturated with a solution of borax. Of the two materials, the 

 Parian cement is by far the better. 



The oil cements, or the mastics, were formerly much used in London, 

 but they have so signally failed that it may suffice to say, that they 

 are composed of a mixture of lime, powdered tiles, litharge, and oil ; 

 they produce a good face for ornamental work in sheltered positions, 

 but they do not resist the London atmosphere, nor have they any 

 valuable powers of resistance as cementitious materials. 



Having thus described the most important among the cements used 

 by civil engineers and builders, we proceed to notice briefly several 

 compositions, intended chiefly to cause the adhesion of surfaces in 

 many departments of the manufacturing arts. Several are described 

 in later articles. [GLUE; LUTES; MASTICH; SOLDER.] Referring to 

 those articles for information on the special subjects to which they 

 relate, we will confine our attention to adhesive compositions of a mis- 



