and sandstone texture, greatly predominating. The coal beds are indiscriminately accompanied by rocks either of sandstone or shale, which often rest upon fire-clay. It is in the shale accompanying the coal that the fossil impressions are so numerous; for they are seldom found in the sandstones, or in the shales considerably distant from the coal beds. The organic remains of coal formation consist of many shells of fresh-water origin. The fossils, with land plants, occur in great abundance and variety, belonging to extinct species, but bearing considerable analogy to those now growing only in tropical climates. These plants are mostly succulent, and are of enormous growth Coal-gas. Carburetted hydrogen, coalgas, when freed from the obnoxious foreign gas, may be propelled in streams out of small apertures, which, when lighted, form jets of flame, and are called gas-lights Coal-tar, tar made from bituminous coal

Coamings, in ships, raised work round the hatches, to prevent water from getting down into the hold Coat. Mast-coat is a piece of canvas tarred or painted, placed round a mast or bowsprit where it enters the deck

Coat, in building, a stratum or thickness of plaster-work

Cob (Cornish), to break or bruise: a cobber, a bruiser of tin. Cobbed ore is spoiled which is broken out of the solid large stones with sledges, and not put to water, being the best ore the same as bing ore in the lead mines

Cobalt.

:

The ancient name for this mineral is not known. Theophrastus mentions its use for staining glass. No cobalt has been discovered in any of the remains of ancient painting. It makes a colour, according to Vitruvius, between scarlet and purple

Cobalt, in chemistry, a metal, when

pure, of a white colour, inclining to bluish or steel gray: at the common temperature its specific gravity is more than 8.5

Cobalt-blue is the name now appropriated to the modern improved blue prepared with metallic cobalt, or its oxides, although it properly belongs to a class of pigments including Saxon blue, Dutch ultramarine, Thenard's blue, royal blue, Hungary blue, smalt, Zaffoe or enamel blue, and Dumont's blue. These differ principally in their degrees of purity, from the nature of the earths with which they are compounded Cobalt-green.

There are two pig

ments of this denomination, the one a compound of cobalt-blue and chromic yellow, which partakes of the qualities of those pigments, and may be formed on the palette Coboose, the place where the victuals are cooked on board of merchant and passenger ships

Cob wall, a wall built of unburnt clay mixed with straw

Cochineal is extremely rich in the finest red colouring matter, and has been long employed in scarlet dyeing, and in the manufacture of carmine

Cochlea, a term used by the ancients to denote something of a spiral form; a spiral pump for raising water, &c.

Cock, or stop-cock, a kind of valve contrived for the purpose of permitting or arresting at pleasure the flow of a liquid through a pipe Cock-boat, a small boat used on rivers Cock-pit, that part of a ship which is appropriated to the use of the surgeon, being the place where the wounded are dressed; it is near the hatchway, and under the lower gun-deck

Cockle, the skiorl of the Swedes and the school of the Germans : a laminated mineral substance of a blackish brown colour, like tin Cocoa wood, the heart of which is seldom sound, is much used in turnery

Coctilis, according to Pliny, a brick hardened by burning Cod-line, an eighteen-thread line Co-efficients, in algebra, are numbers or letters prefixed to other letters or unknown quantities, into which they are supposed to be multiplied; and therefore with such letters, or the quantities represented by them, making a product, or co-efficient product

Cœlum, according to Vitruvius, a soffit or cieling

Cœnobium, anciently a monastery of monks or friars

Cófer, in Cornish mining, a small wooden trough which receives the tin cleansed from its impurities or slime

Coffee-tree, a wood of a light greenish

brown, close-grained, and small in stature, sometimes used by cabinetmakers

Coffer, a deep panel in a ceiling; also

applied to a casket for keeping jewels, and sometimes to a chest Coffer-dam, a hollow space formed by a double range of piles, with clay rammed in between, for the purpose of constructing an entrance lock to a canal, dock, or basin, or for the piers of a bridge Coffin, in Cornish mining, old workings which were all worked open to grass, without any shafts, by digging and casting up the tin stuff from one stall of boards to another

Coffin, a wooden case in which a

dead body is placed, sometimes encased in lead: anciently, stone coffins were used for interment Cog, the wooden tooth of a large wheel

Cog-teeth are formed of a differentma

terial from the body of the wheel : a timber tooth on a cog-wheel is one made of wood, when the teeth stand perpendically to the plane of the wheel

Cog-wheel, an iron wheel with wooden teeth or cogs

Cohesion of fluids. M. Monge and others assert that the phenomena

of capillary tubes are referable to the cohesive attraction of the superficial particles only of the fluids employed, and that the surface must consequently be formed into curves of the nature of linteariæ, which are supposed to be the results of a uniform tension of a surface resisting the pressure of a fluid, either uniform or varying according to a given law

Cohesion, the attraction which takes

place between the particles of bodies, denoting that force by which the particles firmly cohere Cohesion and resistance of fluids, as

examined by the force of torsion. Pressure does not augment the friction; on the contrary, the resistance is greater when the immersion is only partial. Greasing wood does not lessen the friction: the friction of oil is 17 times as great as that of water. A part of the friction is proportional to the velocity: the constant part is almost insensible. Thus a circle ⚫195 metre in diameter, turning in water with a velocity equal to ⚫14 m. in 1′′, meets a resistance equivalent to a weight of 1 gramme acting on a lever of 143 m. The portion proportional to the velocity is equivalent to 042 gr. for a surface equal to twice such a circle moving in its own direction with a velocity of .01 m.

Cohesive strength of materials. The force of cohesion may be defined to be that force by which the fibres or particles of a body resist separation, and is proportioned to the number of fibres in the body, or in the area of its section. Coiling, a serpentine winding of ropes, by which they occupy a small space, and are not liable to be entangled amongst one another in working the sails of a ship

Coin or quoin, the angle of a building; used also for the machicolation of a wall

Coke, charred pitcoal

Coke. The most valuable of the se

condary products of a gas establishment is coke. The best kind is obtained from coal when carbonized in large masses, in ovens constructed on purpose. In a gas manufactory, the production of coke being of minor importance to the formation of good gas, it is generally of an inferior quality to that made in coke ovens, where it is the primary, and indeed sole object for which the coal is carbonized. But gas-coke is excellent for many purposes in the arts and manufactures, producing as clear a fire as that of the first quality, though it is neither so lasting nor so free from slag: for domestic use, however, it is unobjectionable, and may be burnt both in the drawing-room and kitchen with economy and comfort.

The distinguishing characters of good coke are, first, a clean, granular fracture in any direction, with a pearly lustre, inclining to that exhibited by cast iron. Secondly, density, or close proximity of its particles, which adhere together in masses, and specific gravity of 1.10, or rather higher. Thirdly, when exposed to a white heat, it consumes entirely away, without leaving either slag or ashes.

It is invariably the case that the quality of the coke is inversely as that of the gas. The manufacturer must not expect to produce both of the best quality. The process by which the best gas is made generally leaves the coke light, spongy, and friable, although an increase of quantity is gained; for the simple reason, that the degree of heat and other circumstances required to form perfect coke must be entirely changed when gas of a high specific gravity is to be obtained. Thus large masses of coal exposed to a red heat in close vessels are acted upon by slow degrees, the external portions preventing heat from penetrating into the interior until most of the bituminous portions are given off in condensable vapour, or as

charcoal and free hydrogen; the after-products being light carburetted hydrogen, carbonic oxide, and carbonic acid gases. The residue is a carbon of a dense granular composition

Coke, as prepared for use in locomo

tive and other steam engines, may be regarded as purified coal, or coal from which the extraneous matters not conducive to combustion have been expelled by the application of heat. It appears from experiments that the heating power of every description of fuel, whether coal, coke, wood, lignite, turf, or peat, is proportional to the quantity of carbon it contains, and that from 83 to 86 per cent. of this element enters into the composition of any given weight of Newcastle, Durham, or Lancashire coal, the other ingredients being hydrogen, azote, oxygen, and ashes. The exact process which takes place in the conversion of coal into coke is not yet thoroughly understood, although the result can be readily estimated, and is found to depend, to a considerable extent, upon the manner in which the process is performed. Thus, by coking in close ovens, Welsh coal loses about 30 per cent. of its weight; but if the coking be effected in uncovered heaps of coarse lumps, as it often is in the Welsh coal and iron districts (where abundance is allowed, as the excuse for extravagance and waste), the loss of weight is from 50 to 55 per cent. While the weight is thus diminished by coking in close ovens, the bulk is increased from 22 to 23 per cent. The rapid and complete.combustion of the carbon which takes place in the burning of coke has the effect of preventing, to a considerable extent, the emission of that palpable smoke which arises from the combustion of coal, and for this property coke was resorted to for use in locomotive engines, when the non-emission of smoke was imposed as one of the conditions upon which

railway companies were empowered by Act of Parliament. The practical advantages since found to be derived from the burning of coke instead of coal are, its greater power in evaporating water and producing steam, and the less rapid destruction of the boiler which ensues from its employment

Colarin, the little frieze of the capital

of the Tuscan and Doric column, placed between the astragal and the annulets

Cold chisel, a piece of steel flattened and sharpened at one end, which is properly tempered, so that it may be used for cutting metal Cold-harbour, an inn; a shelter from the cold; a protection on the wayside for travellers benighted or benumbed

Cold short iron, iron in an impure state Cold-water well and reservoir. To effect the condensation of steam, the water is very commonly raised, by means of the cold-water pump, from a reservoir or well. This absorbs from the engine some portion of its power. Indeed, when the wells are deep, the quantity of power thus expended is so great, that the condensing system can no longer be judiciously applied. This may be known by the following investigation:

Rule.-Multiply the weight of water, in pounds, by the feet through which it passes in a minute, and divide the product by 33,000; the

NAME.

Abergwilly Arundel.

Cold-water pump, the pump for supplying the water for condensation Collar, in ships, an eye in the end or bight of a shroud or stay, to go over the mast-head

Collar, in turnery, a ring inserted in the puppet for holding the end of the mandril next the chuck, in order to make the spindle run freely and exactly

Collar, a plate of metal screwed down upon the stuffing-box of a steam engine, with a hole to allow the piston-rod to pass through Collar of a shaft, the timber and boarding used to secure the uppermost part of a shaft in loose rubble from falling in Collar-beam, a beam framed across and between two principal rafters Collegiate Churches of Great Britain (list of). The Colleges generally omitted in the Books amount to 130 in number, scattered mostly over England alone, and are consequently not here included.

1375

Sussex