W A K

W A T

( 470 )

w

■\VAKKE._

its colour is generally a deep greenifh-grey,palling to greenifti and greyifh black ; it is alfonot unfrcquently fpotted reddifh or brownifti.It occurs in mafs and cellular; the cells beingeither empty or filled with other minerals. In-ternally it is dull. Its fracture is even, pallinginto uneven and earthy. Its fragments are inde-terminate and blutit-edged. It is opake, ac-quires a little luftre by friftion, is foft and.cafily frangible; it is fomewhat unftuous tothe touch. Sp. gr. 2.53 zrr 2.89. It is readilyfufible by itfelf before the blow-pipe into a blackglafs.

It belongs to the more recent of the rocks oftrap-formation, and not unfrequently inclofespetrified wood and other organic remains. Itoccurs in beds, and veins, and forms the bafe ofmany of the amygdaloids.

The cavities' in the cellular variety generallycontain green earth, calcareous fpar, &c. It isoften mixed with cryftals of bafaltic hornblende,with black mica, magnetical iron ore, andnative bifmuth.

For further particulars fee Trap.

WALKERERCE. See Fuller’s Earth.

WATER. Eau, Fr. Woffer , Germ.

Water at the common temperature is a per-' feftly tranfparent inelaftic fluid, of a very palebluifh-green colour when in large mafles, andentirely deftitute of flavour and odour. In or-dinary circumftances it retains its liquid formonly between the two extremes of 32 0 and 212 0of Fahrenheit’s thermometer, but when fub-jefted to great preflure, as in Papin’s digefter,it is able to fuftain nearly a red heat withoutbeing converted into {team: and on the otherhand when the preflure of the atmofphere isremoved, by inclofing it in an exhaufted re-ceiver, it is convertible into elaftic vapourby a temperature hardly exceeding 70°. Itspoint of congelation alfo may be protracted, bycautioufly cooling it down without agitation,to about 22 0 ; but at this temperature a flightfriction is fuflicient to determine the inftantfolidification of the mafs, which is attended bya very fenfible evolution of heat, as we have{hewn at large in the article Caloric. W ater,like other inelaltic fluids is nearly though notabfolutely incompreflible. The fpecific gravityof water at 6o° is = 1.0, this liquid beinguniverfally adopted as that to which the fpecific^gravities of all other bodies are to be compared,

and by which they are to be adjulted. Otherliquids increal'e in denfity by an uniform pro-greffion according to the cold to which theyare expofed, but in water the period of greateitdenfity is at the temperature of 42 0 F. and fromthis point equal degrees, whether of cold orheat, produce equal changes of ipecific gravity,fo that water at 3 2° and at 52 0 pofiefles thefame degree of denfity. The abfolute weightof a cubic foot of water at 4c 0 , appears fromfome very accurate experiments by LefevreGineau to be = 437102 grs. troy, or .999.09ounces avoirdupois ; and the weight of a likebulk of water at 55° is ftated by Prof. Robifonat 998.74 ounces avoirdupois. The weightof a cubic inch of water at the fame tempera-ture is = 253.03 grs. but according to th«experiments of Sir G. S. Evelyn, as correfted byMr. Fletcher, it is = 252.50 6 . See the Ap-pendix of Weights and Meafures.

At 32° Fahr. as we have already mentioned,water becomes folid, and in doing fo, aflumes atrue cryltailine texture: if a flaik of water befet in a moderate freezing mixture till a con-fiderable part is frozen, and the fluid portionbe then poured off", there will be perceived aci-cular cryftals fliooting from the mafs, andcroffing each other at angles of 60 and 120 de«grees; fometimes alfo, though rarely, theremay be perceived tetrahedral prifms terminatedby dihedral fummits. Ice when at a low tem-perature is confiderably hard, tough, and elaftic:at the celebrated palace of ice conftrufted onewinter at Peterlburgh by order of the late Em-prefs Catharine, there were cannon made of thismaterial, which fuftained feveral difeharges with-out burfting. The fpecific gravity of ice is con-fiderably lefs than that of water,'in confequenceof which it floats upon its furface ; a part of thisbuoyancy, however, is to be attributed to thebubbles of air entangled in its fubftance, whichare difengaged by common water in the aft ofcongelation. The expanfive force of water whileconverting into ice is fo prodigious that its li-mits have not yet been afeertained: the moftinterefting experiments on this fubjeft are thofeperformed by Major Williams at Quebec :*bomb-fhelis about 13 inches in diameter, andwith a thicknefs of metal exceeding 2 inches,were filled with water; the fufe holes werethen plugged up with iron bolts, and the {hellsthus charged were expofed to the open air ata temperature between — 4° 'and — 19 0 : at

* Edia. Phil. Tranf. Vai. II,