Page:Cyclopaedia, Chambers - Volume 1.djvu/843

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FRE

This Intromiflion of a foreign frigorifick Matter they fup- pofe effential to Congelation ; as that which characteriles and diftinguifhes it from Coagulation : The former being effected indifferently by a hot. or cold Mixture ; but the latter only by a cold one. See Coagulation.

Of what kind thefe frigorific Particles are, or how they produce their Effect, is Matter of Debate ; and has given occafion to various Syftems.

Holbs will have it common Air, which intruding into the Water in Congelation, entangles it felf with the Particles of the Fluid; prevents their Motion, produces thofe numerous Bubbles oblerv'd in Ice ; thus expanding its Bulk, and ren- dering it fpecifically lighter: But this Opinion is overtum'd by Mr. "Boyle, who mews that Water will freeze in "Veffels Hermatically feal'd, and into which the Air can have no In- grefs; yet the Bubbles will beasnumcrous herein, as in that froze in the open Air. Add, that Oil is condens'd, in freez- ing : Confequently, the Air cannot there be the Caufe.

Others, and thofe the greatelt Number, will have the freezing Matter to be a Salt ; arguing, that an Excels of Cold will render Water torpid ; but never congeal it, with- out Salt. They are faline Particles, lay they, and thofe diffolv'd and mix'd in a due Proportion, that are the chief Caufe of Freezing : Congelation bearing a near relation to Cryftalli- zation. See Crystallization.

This Salt, they fuppofe of the Nitrous kind ; and to be furnifh'd by the Air, which is generally allow'd to abound in Nitre. See Air, and Nitre.

How the Particles of Nitre may prevent the Fluidity of Water, is pretty eafily accounted for : Thefe Particles are fuppos'd to be fo many rigid, pointed Spicula, which are eafily driven into rhe Stamina, or Globules of the Water ; which thus becoming variouily mingled and entangled there- with, by degrees infeeble and deftroy the Motion thereof.

TheReaion this Effect only arifes in fevere Winter Wea- ther, is, that 'tis then only, that the retarding Action of the nitrous Spicula, is more than equal to the Power or Prin- ciple whereby the Fluid is ctherwife kept in Motion, or diipos'd for Motion. See Fluid.

This Opinion is fupported by the knqwn Experiments of Artificial Freezing.

A Quantity of common Salt or Petre being mix'd with Snow, or Ice pulveriz'd ; and the Mixture diffolv'd by the Fire : Upon immerging a Tube full ofWater in theSolution ; the Water, that Part of it next the Mixture, prefently freezes, even in warm Air. Whence it is argued, that the Spicula of the Salt, by the Gravity of the Mixture, and of the in- cumbent Air, are driven thro' the Pores of the Glafs, and mix'd with the Water: For that it is the Salt has the Effeft, is evident; inafmuch as we know affuredly that the Particles of Water cannot find their Way thro' the Pores of Glafs. In the r e Artificial Freezings whatever Part the Mixture is ap- plied in, there is prefently produe'd a Skin, or Lamina of Ice ; whether at top, or bottom ; or on the Sides : By rea- fen there is always a Stock of faline Corpufcle, fufficient to overpower thefe Corpufcles of Fire : But Natural Congela- tions are confin'd to the Top of the Water, where the Salt molt abounds.

Againft this Syflem the ingenious Author of the Nonvelle ConjcStire pur Expliauer la Nature de la Glace, objefls, That it does not appear, that Nitre always enters the Com- pofition of Ice; but that if it did, it would come fhort of accounting for fome of the principal Effects. For how, for inftance, fliould the Particles of Nitre by entering the Pores of Water, and fixing the Parts, oblige the Water to dilate and render it fpecifically lighter? Naturally they lliould aug- ment its Weight. This Difficulty, with fome others, fhew the Ncceffity of a new Theory. That Author, therefore, advances the following one, which feems to folve thePhx- nomena in a more ealy, and fimple manner ; as not depend- ing on the precarious Admiffion or Extrufion of any hetero- geneous Matter.

III. Water, then, freezes in the Winter only, becaufe its Parts being more clofely join'd together, mutually embarrafs one another, and lofe all the Motion they had : And the Caufe of this clofer Union of the Water, is the Air • or rather an Alteration in the Spring and Force of the Air. '

That there are an infinite Number of Particles of grofs Air, interfpers'd among the Globules of Water, is abun- dantly evident from Experiment: And that each Particle of Air has the Virtue of a Spring, is confeis'd : Now, this Author argues, that the fmall Springs of grofs Air mix'd with the Water, have more Force in cold Winter Weather, and unbend themfelves more^than at other times. Hence, thofe Springs thus unbending themfelves on oneSide, and the ex- ternal Air continuing to prefs the Surface of the Water on the other ; the Particles of Water thus conftring'd and lock'd up together, muff lofe their Motion and Fluidity, and form a hard confiftent Body : Till a Relaxation of the Spring of the Air, from an Increafe of Heat, reduce the Particles to

their old Dimenfions, and leave room for the Globules to flow again.

But this Syftcm has its Foible : The Principle on which it ftands, may be demonftrated to be falfe. The Spring, or Elafticity of the Air is not increas'd by Cold ; but diminiuYd. Air expands it felf by Heat ; and condenfes by Cold : And 'tis demonftrated in Pneumaticks, that the elaltic Force of expanded Air, is to that of the fame Air condens'd ; as its Bulk when ratify 'd, to its Eulk, condenfed. See Elasti- city, and Air.

We don't know, whether it is worth mentioning, what fome Authors have advane'd, to account for the Increale of Bulk and Diminution of fpecific Gravity of frozen Water : viz. That the aqueous Particles, in their natural State, were nearly Cubes, and fo fill'd their Space without the Jnterpo- fition of many Pores : But that by Congelation they are ' chang'd from Cubes, to Spheres ; whence a Neceffity of a deal of empty Space between them. Cubic Particles are certainly much lefs proper to conftitute a fluid, than fpherical ones; and fpherical Particles \ck difpofed to form a fix'd, than cubic ones.

Thus much the Nature of Fluidity and Firmnefs eafily fuggefts.

After all, for a confiding Theory of Freezing, we mult recur either to the frigorific Matter of the Corpufcularians; conflder'd under the Light and Advantages of the Newto- nian Philofophy : Or to the tetherial Matter of the Carte- fians, under the Improvements of Monf. Gautcron, in the Memoires de (Academic Royale des Sciences, An. 1709.—

Each of which we fhall here fubjoin ; and leave the Rea- der to make his Choice.

For the firji : A Number of cold, faline Corpufcles being introdue'd into the Interfaces between the Globules of Wa- ter ; may be fo near each other, as to be within the Spheres of one another's Attractions ; the Confequence of which mult be, that they will cohere into one lolid, or firm Body : Til], Heat afterwards feparating them, and putting them into va- rious Motions, breaks this Union, and feparates the Particles fo far from one another, that they get out of the Diltance of the attracting Force, and into the Verge of the repelling Force ; and then the Water re-affumes its fluid Form.

For, that Cold and Freezing do arife from fome Sub- ftance of a faline Nature floating in the Air, feems proba- ble hence, that all Salts, and more eminently fome parti- cular ones, when mix'd with Snow, or Ice, do prodigioufly increafe the Force and Effects of Cold : Add, that all faline Bodies do produce a Stiffhefs and Rigidity in the Parts of thofe Bodies, into which they enter.

Microfcopical Obfervations upon Salts rttanifeff, that the Figures of fome Salts, before they /hoot into Maffes, are thin, double, wedge-like Particles, which have abundance of Surface with refpect to their Solidity (the Reafon why they fwim in Water, when once rais'd in it, tho' lpecifically heavier). Thefe fmall Points of the Salt getting into the Pores of the Water, whereby aifo they are in fome meafure fufpended in the Winter time (when the Heat of the Sun is not ftrong enough to diffolve the Salts into a Fluid, to break their Points, and to keep them in perpetual Motion) being lefs disturbed ; are more at Liberty to approach one another; and by Ihooting into Cryftals of the Form above mention'd, do, by their Extremities, infinuate themfelves into the Pores of Water, and by that means freeze it into a fblid Form.

Further, there are many little Volumes or Particles of Air, included at feveral Diftances both in the Pores of the watry Particles, and in the Interfaces made by the fpherical Figures. By the Infinuation of thefe Cryftals, the Vo- lumes of Air are driven out of the watry Particles ; and many of them uniting, form larger Volumes, which there- by have a greater Force to expand themfelves, than when difpers'd ; and fo both enlarge the Dimenfions, and leflen the fpecifick Gravity of the Water, thus congealed into Ice. Hence alfo we may conceive, how Water impregnated with Salts, Sulphurs, or Earths, which are not eafily dif- folveable, may form itfelf into Metals, Minerals, Gums, and other Fofftls ; the Parts of thefe Mixtures becoming a Cement to the Particles of Water, or getting into their Pores, change them into thefe different Subflances.

For the fecond: As an tetherial Matter or Medium is ge- netally allow'd the Caufe of the Motion of Fluids ; fee Me- dium : And as the Air it felf has all its Motion from the fame Principle ; it follows, that all Fluids muft remain in a State of Reft, or Fixity, when that Matter lofes of its necef- fary Force. Of confequence, the Air being lefs warm'd in the Winter time, from the Obliquity of the Rays of the Sun ; the Air is denfer, and more fix'd in Winter, than any other Seafon of the Year.

But further, from divers Experiments we have learnt, that the Air contains a Salt, fuppos'd to be of the Nature of Nitre. This granted, and the Denfity of the Air allow'd, it follows, that the Molecules of this Nitre muft likewife

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