CRY

CRY

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particles, eacli of which is again compofed ofelementary ones. Thus a mafs of muriated fodaconfifls of a vail multitude of little cubes, whichare its integrant particles, each of which isrefolvable into muriatic acid and foda, whichare its elementary particles. Witli the latter ofthefe cryllallization has nothing to do, nor is itpoflible to afcertain their forms, fince they arenot decompofable by means which have anyrelation to form. Thus when a piece of com-mon fait is pounded in a mortar, the concuf-fions that it receives are continually deftroyingthe adhefion between its integrant particles, andthough perhaps it is incapable of being actuallyand compleatly refolved, on account of thecomparative coarfenefs of the inltruments thatwe are obliged to make ufe of, yet we fee anevident approximation to this, and cannot doubtthat a continuance of the fame means withmore perfect inltruments would be compleatlyefficacious. Now a body that is mechanicallydivifible muft be produced by the adhefion ofaggregation of its conftituent particles, andthefe, both with regard to their forms and themanner in which they adhere to each other, areproper objects of meafurement and mathematicalcalculation. The cafe however is widely dif-ferent with regard to the elementary particlesof which the integrant ,moleculse are compofed :thefe are incapable of being in the fmalleftdegree feparated by percuffion or any kind ofmechanical force, and therefore the mode oftheir combination is not capable of being ex-plained by geometrical calculation.

All the integrant particles of the fame fub-llance are of the fame figure, and the greatvarieties that appear in its cryllalline forms areowing to the different modes in which its par-ticles are aggregated upon each other. This isevident, becaufe by dividing the moll complexcryltals in the direction of their lamina;, a re-gular figure called the nucleus or primitivefigure will be at length produced, which is fur-ther divifible only in a direction parallel to its(ides, and the correfponding angles of which inany number of fpecimens will be found to beItriCtly equal. But though the nuclei of allcryltals belonging to the fame fpecies accuratelycorrefpond with each other in their form andthe dimenfions of their angles, yet it is by nomeans true, as has been haltily alferted, thatevery fpecies has a peculiar primitive form.Thus boracite, muriat of foda, galena and ironpyrites have the fame primitive form, namely acube, and the fame integrant molecule which isa cube alfo. In like manner fluor fpar, alum,

fpinelle ruby, diamond, ruby copper, bifmuthand antimony afford by calculation and mechani-cal divifion a regular otlohedron for their pri-mitive figure, compofed of regular tetahedralintegrant particles. With the exception how-ever of thefe nuclei, which are regular geo-metrical folids, and therefore unfufceptible ofany variety in their dimenfions, it may be af-firmed that no two nuclei of different fpecieshave precifely the fame dimenfions; thus theprimitive form both of calcareous fpar and tour-maline is an obtufe rhomboid, but in the formerthe obtufe angles are = ioi° 3while in thelatter they are = x 13° 34'. The primitiveforms that have hitherto been obferved are thefollowing: 1. the cube; 2. the regular o&o-hedron ; 3. the regular tetrahedron •, 4. therhomboidal dodecahedron ; 3. the rhomboid ;6. the oCtohedron compofed of two pyramids,with fquare, rectangular or rhombic bafes; 7.the tetrahedral prifm either ftrait or oblique,with fquare, rectangular or rhombic bafes ; 8.the regular hexahedral prifm; 9. the pyramidaldodecahedron.

It has been the praCtife of fome late authorsto extend the meaning of the term cryllallizationfo as to make it fynonimous with the attractionof aggregation ; this however appears to be in-judicious ; the latter comprehends every fpeciesof formation by which folids are produced, butthe former exprefles only that regular arrange-ment of homogeneous integrant particles bywhich, when interrupted, cryllalline laminae,and when uninterrupted, entire cryltals, areproduced ; aggregation therefore includes cryf-tallization, which is only a mode or fpecies ofthe former. It is of importance to bear in mindthat not only a regular external figure, but aregular internal llrufiture is neceffary to conlli-tute a cryltal; otherwife a column of bafaltmight be confidered as a prifmatic cryftal, anerror which fome of the older mineralogifts haveactually fallen into.

The integrant moleculse of different fubltancesappear to be poffeffed of very different degreesof cryllalline polarity; the relative force ofwhich may be ellimated in fome meafure fromthe comparative .quantity of extraneous matterwith which they may be intimately mixed with-out annulling their power of cryllallization, andpartly alfo from the proportion which cryltalsof any fpecies bear to the uncryllallized maffesof the fame. For this reafon carbonat of limemay be confidered as endowed with a highdegree of cryllalline polarity, for not only arecryllals of this fubltauce exceedingly abundant