CL A
CO A
( 296 )
6 . Marly clay.
The colour of this is bluifh or brownifh red:it occurs either compact or foliated: it has afo'ft unctuous feel, takes a polifh by frictionwith the nail, is very plaftic, more or lefs gritty,though not fo much fo as the common alluvialclay. It burns to a brick of a buff or deep creamcolour, and at a high heat readily enters in-to fufion. It effervefces ftrongly with acids,and contains from L to X V of carbonated lime.It originates fometimes from the decompofitionof compact argillaceous limeftone, but morefrequently from the fofter fiaty varieties ufually■called ftone marl. It is largely employed as amanure, and where the calcareous part doesnot exceed io or 12 per cent, it is efteemed asa material for bricks.
7. Clay from metallic veins.
Its colour is grey verging into bluifh, gveenifhfind yellowifh, or red. It has a fmooth un£tuousfeel, is very tenacious, often contains fulphuricacid and certain metallic oxyds which are neverobferved in other clays, fuch as lead, filver, an-timony, copper, and bifmuth. Is found inmetallic veins.
8 . Alluvial clay.
The circumftances which characterize allu-vial clay are the following. It contains a largerproportion of quartzy fand than the preceding,rounded pebbles of various kinds are alfo im-bedded in it; thus fhowing it to have been car-ried from its native fituation and mingled in itsptogrefs with a variety of extraneous bodies.At leaft three kinds of it may be diftinguifhed,viz. Pipe clay, Potter’s clay, and Chalky clay.
Pipe clay is of a greyifh or yellowifh whitecolour, an earthy fracture and a fmooth greafyfeel: it adheres pretty ftrongly to the tongue,is very plaftic and tenacious •, when burnt is ofa milk-white colour; is difficultly fufible, thoughmuch more fo than porcelain clay, from whichit is further diftinguifhed by its fuperior plaf-ticity and the fand which it contains. It ismanufadtured into tobacco-pipes, and is thebafis of the white or Queen’s-ware pottery.
Potters’ clay is of a reddifh, bluifh or greenifhcolour, has a fomewhat fine earthy fraffure, and3 foft, often greafy, feel: it adheres to thetongue and is very plaftic. It burns to a hardporous red brick, and in a higher heat runs intoa dark-coloured flag. When tempered withwater and mixed with fand it is manufacturedinto bricks: thofe varieties that are the rnoftfree from pebbles are made into tiles and coarfered pottery.
Chalky clay ia of a leaden blue colour, anearthy frafturc and a meagre feel: it is plaftic,but breaks down by expofure to the weather.It contains a large proportion of fand and round-ed pieces of chalk of all fizes up to that of ahazle nut. It effervefces ftrongly with acids,burns to a red porous brick, and is very fufible.It is ufed as a manure in the counties of Lin-colnfhire, Norfolk , and Suffolk.
CLAY pure. See Argil native.
CLAY fiaty. See Shale.
Its colour is greenifh, bluifh, or afh-grey, orbrownifh-red; it is fometimes marked by brown-ifh yellow fpots and ftripes. It occurs in mafs.Its fracture is fine grained earthy paffing intoeven, fiaty or fplintery: fome varieties are flatconchoidal. It is opake, dull, frangible andfoft; has a meagre feel and does not adhere tothe tongue.
It forms large mountainous mafles, occurringin beds, veins, and as the bafis of clay porphyry.It paffes into fhale and jafper, and decompofes.into clay.
CLYSSUS OF NITRE. The term clyfusufed by the old writers in chemiftry and alchemyis defined to be a the vapours that arife fromthe detonation of nitre with any inflammablefubftance; the clyfus of nitre, the vapours fromnitre and charcoal (for which fee Nitrous Acid ),the clyfus of fulphur , the vapours from fulphurand nitre, &c. The term is now obfolete, butmodern chemiftry ftill derives great advantage,in many cafes, from this mode of decompofitionby nitre.
Coagulation is the folidification of a liquidproduced without evaporation, and without itsaffuming a cryftalline form. The fuddenhardening of the white of egg by mere heat isa familiar example of the kind. The term isfometimes applied alfo to a very fudden andconfufed cryftallization, in which the cryftal-lized particles appear amorphous to the nakedeye, though when examined with a glafs theyexhibit fome regularity of form. Thus, whenftrong fulphuric acid is added to a very con-centrated folution of potafh, the whole coagu-lates immediately to a nearly folid mafs ofgranular cryftals of fulphat of potafh.
COAK. Pit coal deprived of its volatile in-gredients by charring in the open air or in anoven, is converted to a light porous fpungy mafscalled coak or cinders. For further particularsfee Coal .
Macsjucr. Chem. Did;.