Page:Cyclopaedia, Chambers - Supplement, Volume 1.djvu/570

 CRY

CRY

to fome folid body, and terminated at the other, by an hex- angular or pentangular pyramid.

The genera of the firft order are two : i. The macrotelo/lyla, or perfect cryjiah, with a longer intermediate column 2. The brachytelo/lyla-, or thofe with a fhorter intermediate column. Thofe of the fecond order are alfo two: i. The paura'c- dryjiyla, which are dodecahedral cryjlalh, compofed of two hexangular pyramids, joined bafe to bafe, without any intermediate column. 2. The polyedrajiyla \ thefe are hexa- decahedral cryjiels t compofed of two octangular pyramids, join'd bafe to bafe, without any intermediate column. Thofe of the third order are five. i. The ellifomacre/fyla. Thefe are dodecahedral cryjiah, with thin hexangular columns, terminated by hexangular pyramids. 2. The ellipopachyjiyla. Thefe are dodecahedral cryjiah, with thick hexangular co- lumns, terminated by hexangular pyramids. 3. The ol'ige- dra. Thefe are decahedral cryjiah, with thick pentangular columns, terminated by pentangular pyramids. 4. T hepan- gonia. Thefe are tetraicofihedral cryjiah, compofed of dodec angular columns, terminated by dodecangular pyramids. 5. The arthrodia. Thefe are dodecahedral cryjiah, with very Ihort and flender columns, and moderately long pyramids, generally found cluftered together on the furface of cryftalline or ftrong roundifh nodules, or incruHing cavities within fuch. Thefe are called by fome echinated and concave iryjlalline balls. i#/'sHift of Kofi: p. 153, feq.

Adding to thefe regular genera, the accidental varieties of cryjiah, owing to the admixture of metalline particles, influ- encing their mape as well as colour; the three principal of wlich are thofe impregnated with lead, iron, and tin ; the firft cubic, the fecond rhomboidal, and the laft quadrilateral py- ramids, without columns ; we have the whole feries of the figured cryjiah : the firft of thefe are called molybdia, the fecond Jideria, and the third cajfiteria. Befide all thefe, cry- jial is alfo fometimes found in a pebble-like form, which is an accidental variety, like thofe in the chryftallizations of falts, where many concretions entirely want their naturally angular form.

The origin and formation of cryjiah, as to the time and manner of them, defervc a very nice enquiry, fince many of the more compound foffile bodies are principally compofed of cither cbrv/ial or fpar, a body in many things refembling it; and the afecrtaining the great queftion, whether it was all formed at one time, and that long fince, or does continue to ■ be formed at this day, will fo far alfo afcertain the time of the coaiefcence of thofe other bodies, of which it is the bafis. The original coaiefcence and formation of thofe bodies of which fpar is the bafis, we well know may have been but of yefterday, fince we have evident proofs, that fpar is concre- ting to this day, and that fparry bodies are forming every mo- ment. This is evident, from the fparry ftalaclitje in the ar- ches of modern buildings, particularly in one fo lately built as the new bridge at Weftminfter, the roofs of the arches of which were filled with thefe fpars within a year after the arches were built; and there are evident proofs, that fpars are not made of matter cdued from the ftone, fince brick arches equally abound with them ; and the brick vault which fup- ports part of the grand terrace at Windfor, has been of late found fo full of them, that there was not room to walk for them. See the article Stalactites, Cycl. From thefe obfervattons, as alfo thofe of the fparry incruftations round vegetable, and otherbodies in fprings, and at the bottoms of our tea-kettles being all incrulred with it; -we have evident proof, that fparry bodies are form'd to this day, but we have no fuch clear evidence of the preftnt growth of cryjiah Whether or not it is fo, however, we may be led by a few piopofi- tions to prove, by the only fure telf, experiment.

1. If cyjlal and fpar can be at this day diffolved in water, or fufpended in it, in their minima or ultimate particles, and again feparated from it, then ftony or other foflils compofed or cryjial and fpar, may be form'd at this day : if thefe bodies are not thusdiflblved, they cannot.

2. If cryjial and fpar can be raifed in vapour, or fufpended in effluvia, then cryftalline and fparry concretions may at this day be formed in places where water cannot be fuopofed to have come ; if they cannot be thus fufpended, then the cryjiah and fpars found in fuch places cannot have been form'd at this day, but muft have been there from fome di- ftant time.

The fubjedt of enquiry is by thefe propositions reduced to a narrow compafs; and all that experiments have to determine is: 1. Whether chyjlal or fpar are at this time found fufpend ed in water, in imperceptible particles, or whether they are not ; and 2- If they are thus fufpended, whether they are or are not capable of being raifed in vapours, Thefe things Dr. Hill has been at the pains to determine, by a great number of experiments.

The bottom of every tea-kettle, as has been before obferv'd, " informs us, that fome folid foffile body is fufpended in imper- ceptible particles in all, even the cleareft water, and is eafily feparated from it by no other agent than heat ; as heat there- fore is found capable of feparating this fubftance, and no other agent that we know of is fo, that is, the natural means to be uied in the inveftigation of the fubject.

The fubftance encrufling tea-kettles, &c. is found to be a genuine fpar, with a greater or leffer admixture of earth, and is wholly the fame with the encruftations on vegetables in fpring^. &c. Here therefore, is a proof of fpar and earth being fufpended in common water, but none of cryilal. This was alone to be determined by repeated and cautious diftillations. In difiilling the water of the fame fpring, with different de- grees of fire, a different quantity of matter was found left at the bottom of the vefiel. It appeared hence, that in a greater degree of heat, a great part of the matter had been raifed in vapour, and the remainder on tryal, always proved to be only fpar and earth. Here were therefore, both the que- ftions anfwered in the affirmative, in regard to fpar, viz. that it is continually fufpended in water, and may be raifed in vapour. The water of thefe diftillations being returned nro the cucurbit, and rediftilled, leaves a fecond fediment in fmall quantity, and of a whiter colour. This being examined ac- cording to the known laws of foflils, proves to be part fpar, and part cryjial, an undhTolv'd powder remaining from it, after pouring on aqua fortis to take up the fpar; and this in all tefts appearing to be true and perfectly pure cryjial A third diftillation of the fame water, produced not the leaft refi- duum. Hence therefore, it is evident, that cryjial as well as fpar is continually fufpended in water, and may be raifed in vapour, and feparated by no other agent than heat. And hence the conclufion is plain, that c-yjlall m as well as fparry bodies may be, and doubtlefs are, continually form'd in the earth to this day, and need not be fuppofed all of as old a date as the creation or deluge. fcOWs Hift. of Foff p 157. Having thus from experiments gone thro' the hiftory of what may be the origin of many of the cryjlalline bodies we daily- meet with, it remains to fay fomething of their form. The perfect regularity of the figures of cryjiah, cannot but be the efrect of fome fixed, permanent and invariable c.ufe; thefe being ever, unlefs altered by accidents, which rarely happens, the very fame in the fame genus. The antients efteemed cryjial a congelation of water, and thought it only ice harder than ordinary. Signior Lana, who had an oppor- tunity in the Val-fabbia, of feeing many of the perfect double pointed kinds, imagined, that they owed their origin to dews congealed by nitrous exhalations. Rohault imagines the figure of common cryjial the effec"t of fix drops of water thrown together.

Others are for its being formed of radiations ; others, from all its parts being like the whole ; and others from the mu- tual tendency of the parts of it toward the fame center. But all thefe the laws of action in matter, and the ftruclure of cryjial in the feveral fpecies, eafily fhew to be erroneous. Many think they have folved all difficulties, when they fay, that cryllah are falts ; but we know no more of the true caufe of the figure of falts, than we do of thofe of cry/la's. And it is to be added, that if cryjiah are falts, then falts are fome- thing elfe from what we have been taugr.t to think they are, cryjiah by no means anfwering to the definitions given us of them by authors. As we yet know fo little of the caufes of the regular cryftali/ations of falts, why are we to fuppofe no other bodies but falts capable of fuch equaliza- tions; and why may not the fame almighty agent, who has implanted in the minima of faline bodies, a tendency to thefe their feveral appropriated forms, have allotted the fame ten- dency to other bodies ?

How is it, that cryjial, in its fmalleft concretions, obtains its determinate figure, according to the genus it is of, is affured- ]y yet to us unknown ; but how it is enlarged afterwards, yet ftillkept in its fame form, feems not to be (o difficult to be accounted for, and may indeed be traced from obfervations of the federal bodies in their prefent ftate. We are not to doubt, but that the fmalleft; concretions are regularly formed in all cryjiah, according to their kinds, and we fee the fmalleft that even the microfcepe can difcover to us, regularly are fo. .Thefe are formed among water or va- pour, folid with the fame particles, and only wanting a flow evaporation to part them from the water or vapour. Thefe particles, though when collected in a body, they be of more than twice the fpecific gravity of water, yet while fufpended in a vaft proportion of water, attract the parti- cles of the water more ftrongly than they do one another, and hence give way to that repulfive power fo well known in nature, which is properly the effect of another attraction, by which all things are made to afcend in water, which are lefs than water attracted by the gravitating power of the earth : the particles of cryjial therefore attracting the parti- cles of water more ftrongly than one another, recede from one another as far as the quantity of water they are fufpend- ed in will permit. When this quantity of water is fo far eva- porated, that the particles of cryjial are nearer bs one another, and brought within the verge of one another's attraction, they become more attracted by one another than by the par- ticles of water and thence form concretions. This they ufual- ly do in many parts of the fame fluid at once; and hence it is, that we ufually find many fhoots in the fame place. The whole cryftalline matter might now be expected to form itfelf into thefe fmall concretions : but there is now a new law or power eitablifhed in die evaporating fluid ; for thefe fmall ag- gregates