CHALK, an opaque mineral, of a yellowish white, or rather of a snow colour, of a fine earthy fracture, without lustre, breaking into blunt-edged angular fragments ; when contaminated with iron, it has more or less of an ochrey tinge, and stains the fingers ; but when pure it is very soft and almost friable, gives a white streak, has a meagre feel, and adheres to the tongue. It effervesces violently with acids; and when mixed with iron becomes harder and heavier : its specific gravity varies from 2 • 4 to 2 • li. It occurs generally in a mass, sometimes disseminated, or invest ing other minerals.
In a state of purity, it appears to be oomposed only of water, lime, carbonic acid. and a small quantity of illumine. N r. Kirwan obtained the ffillowing analysis : Chalk occurs in thick beds, nearly horizontal, alternating with thin layers of flint nodules, which are also irregularly dispersed through its substance. It contains a vast quantity of the relics of disorganized marine bodies, and often the hard parts of amphibious and land animals, as the heads and vertebra! of crocodiles, elephants' teeth, &c.
Chalk beds occur frequently in the cast and south puts•• of England, in the north-east of France, in Poland, and in some parts of the Danish islands.
Its uses are numerous; it is employed in walling or vault ing, as building-stone ; many of the groins or vaults of our Gothic churches are constructed with it ; it is also employed in the composition of mortar, in countries where lime-stone is less abundant ; and when well burnt, is found not much inferior to lime-stone.
CI IA (from the Latin camera, derived from the Greek Kattapa, a vault, or curve,) a vaulted apartment, a part of a lodging. This term was formerly applied to any room, and sometimes even to a suite of apartments ; but in modern times it is used to designate rooms ordinarily intended for sleeping in. The proportion of its horizontal dimensions may
be varied, to accommodate different circumstances, which may occur either in the form of a building. or in the disposi tion of the apartments, from the square to the proportion, of which the breadth is two-thirds of the length ; its altitude may be three-fimrths of the breadth. The word originally implied a vaulted apartment.
In building bed-chambers, the situation of the bed, as well as of the fire-place, ought to be attended to, as should the disposition of the windows, when they can be shifted without deltroying the symmetry of the exterior. If the bed and fire-place be opposite to each other, the fire-place may be in the middle of its own side ; but if it 'should be found neces sary to have the bed on the same side of the room with the fire-place, on account of doors or windows, or both, then the chimney ought to be placed in the middle of the remaining distance between the bed and the wall, the bed being sup posed to stand at one extremity. The situation of doors may be the same as in other apartments ; passage-doors should be within about two feet of the angle of the room, on whatever side they are made ; and may either be on the same side with the fire-place, or on the opposite side to the fire-place, or in the return side, opposite to the window, next to the farther corner from the fire-side of the room.
The bed ought to he so placed as to be out of the current of air, which usually rushes from the door to the fire-place.
The most eligible figure of chambers, for furniture, is the rectangle ; though sometimes the circle, ellipsis, or octagon, may be allowed to some particular room, for the sake of variety. Besides passage-doors, it is convenient for cham bers to communicate with each other, or with a dressing room.