CRY
C YM
( 560 )
a mutual decompofition, muriat of magnefia adeliquefcent fait, and fulphat of foda an efflo-refcent one, will be formed, and the flight cryf-talline force of the latter will be almoft whollyannulled by the extreme folubility of the former.
It has been already mentioned that the dif-turbance occafioned by ebullition and othercaules of agitation prevents the formation ofregular cryftals: the converfe however of thisis not true, namely that the entire abfence ofexternal motion is peculiarly favourable to regu-lar cryftallization. The folutions of tliofe faltsthat are much more foluble in hot than in coldwater, and have but a feeble power of cryftal-line polarity may, if kept ftill, be cooled bydegrees confiderably below their congealing orcryftallizing point, and ftill retain their fluidity-,apparently, becaufe the attraction of their par-ticles, in itfelf feeble, and oppofed by the affinityof the water, is held in equilibrium becaufe noone particle has a preponderating power overthofe in its vicinity; for if a piece of the famekind of fait that is contained in the folution beintroduced even with the utmoft precaution, thefuperior attraction of the mafs will be imme-diately exerted on the neighbouring particles,and a rapid growth of cryftals will take place,radiating from this mafs as their centre of at-traction, Cryftallization may alfo be inducedin fimilar circumftances merely by agitation,but when this is the cafe it is always confufedand irregular.
For further particulars connected with thisfubjeCt fee Affinity, Solution, Precipita-tion.
CUCURBIT is an article of chemical appa-ratus. (See the Appendix .)
CULM. See Coal.
CUPEL is a fmall crucible ufed in the pro-cefs of cupellation.
CUPELLATION. Abtreiben , Germ. Thisimportant procefs in metallurgic chemiftry isdescribed at length under the article Assay.
CURCUMA. See Turmeric.
CYANITE. a Kyatiit, Werner. Sappare,Sauflure. Di/ihene, Hauy.
Its colour is milk-white, pearl-grey, bluifli-grey, or fmalt-blue, Pruffian blue or Iky-blue.It lbmetimes occurs entirely blue, but more
frequently fpotted, ftriped or clouded with thiscolour. It is found in mafs, difi'eminated, andcryftallized in long oblique four-fided prifms,truncated on the lateral edges. The cryftalsare imbedded or interfeft one another, and varyfrom middle-fized to very fmall. Its externaland internal luftre is bright-fhining pearly. Itsfracture is broad diverging and interieftingradiated, palling into curved-foliated. The frac-ture of the cryftals is foliated in three directions.Its fragments are flaty and fometimes imper-fectly rhomboidal. In mafs it. is ufually tranf-lucent; the cryftals are for the molt part tranf-parent. Its hardnefs is about equal to that offluorfpar. It has a flight degree of flexibility,and feels fomewhat greafy. Sp. gr. 3.51 to3.62.
It is infufible per fe before tlie blowpipe. Itscomponent parts, according to Theodore deSauflure, are
29.2 Silex,
55. Alumine,
2.25 Lime,
2. Magnefia,
6.65 Oxyd of iron,
6.9 Water and lofs.
100.00
It occurs in primitive mountains imbedded inmicaceous fchiftus and accompanied by grena-tite.
It is found near Banchory in Aberdeenlhire,and in the largeft of the Shetland iflands alfoin Norway , the Swifs Alps, the Pyrennees, theTyrol, Carinthia, Bavaria, France and Siberia .
The very pale varieties of this mineral arefometimes miftaken for tremolite; it may bediftinguiffied however by the blue tinge whicheven the paleft are not entirely free from : be-fides tremolite is found chiefly in granular lime-ftone, but cyanite in micaceous fchiftus. Thetranfparent varieties of a Pruffian blue colourare fometimes when cut and poliffied fold forfapphires, from which however they are readilydiftinguifhed by their inferior hardnefs and fpe-cific gravity.
CYMOPHANE. See Chrysoeeryl.
• Hauy, Brochant, Emmerling, Jamefon.