Page:Cyclopaedia, Chambers - Supplement, Volume 1.djvu/760

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£REE (Cytl.)— Free, aboard a fhip. The Teamen fay the pump frees the fhip, when it throws out more water than leaks into her j but, on the contrary, when it cannot throw out the wa- ter as faft as it leaks in, they fay the pump cannot free her : alfo bailing or lading out water out of a boat, is called freeing the boat.

FREE-bord, Franchsrdus, is ground claimed in fome places, more or lefs, beyond, or without the fence: it is faid to contain two foot and a half. Mon. Angl.Tom. 2. p. 241.

"FREE-Jh/ie. The qualities of the feveral kinds of free-Jlonc in common ufe in the feveral parts of Europe are very different. They all agree in this general property indeed, that they are fofter while in the quarry, than when they have been fome time expofed to the air : but even this general property differs greatly in degree. They have a fort of grey free-Jtone in ufe at Paris, of which we do not feem yet to have met with any quarries in England, though probably enough there are fuch, which has this property in fo eminent a degree, that the expence of working it is in a great meafure faved. This ftone lies every-where on the fouth fide of the river Seine, and is of a coarfe and large grit. It is fo foft when newly taken out of the ftrata, that they cut it very conveni- ently with a fort of broad axe, and fafhion as many ftones for building in this manner in an hour, as an equal number of our people do in a day or two. Though this ftone is as foft as dry clay when firft taken up, it is found to harden fo confi- derably in the air, that it becomes more than equal to our or- d'mary free-Jione.

Our Portland ftone of the fineft kind, which is white, and of a clofe grit, is very fit for hewing or carving i but it will nei- ther refill water nor fire, which is a very fingular circumftance in fo denfe a ftone ; while the free-J?tme of Kent, which is lefs beautiful to the eye, and is of a greyifh colour, and confidera- bly clofe, tho' of a larger grain, refifts the air and water very well.

The free-Jlone of Derbyfhire, on the other hand, is fo brittle as to be unfit for any fine working, and fo coarfe and open in its texture that it lets water through j yet it bears the fire ex- tremely well, and is fit for ovens, hearths, &c. Phil. Tranf.

FREEZING (Cyel.) — A degree of cold fufficient for this may be procured in all climates, and at all feafons of the year, by this means. Let a quantity of dry powder'd fal armoniac be feparately included in one glafs, and a proper quantity of com- mon water in another. Let both thefe glafles be placed in a fo- lution of other fal armoniac in water while the fait is d invol- ving; both the confined fait and the water will by this means be brought to the fame ftate of cold with the folution ; and being then mixed together, they will form a fecond folution much colder than the firft. And this may be made the liquor for another quantity of fal armoniac and of water to be placed in, which being afterwards mixed, and the fame procefs re- peated, the cold may be brought to a degree proper for freez- ing in any climate or feafon. Shaw's Lectures, p. 78. Nothing is more commonly known than the method of con- gealing liquors into ice by an artificial froft even in the warm- eft feafon ; but it does not feem to be yet known what are the falts moil efficacious of all on this occafion, or, in other words, what fait is capable of producing the greateft degree of artificial cold, or in what manner it may be beft ufed, and what proportion it ought to bear with the powder'd ice or fnow that is ufed on the occafion. The common procefles are known, but few have enquired fo curioufly into the whole as fo nice a fubject feems to deferve.

Mr. Reaumur at length took the whole into confideration, and examined the various degrees of cold by a nice thermometer, whic.'i being placed in the liquor to he frozen^ fhewed very exactly the degree of cold by the defcent of the fpirit. Salt petre ufually panes for a fait that may be very ferviceable in thefe artificial congelations ; but the experiments of this gentleman prove, that this is an erroneous opinion. The moft perfectly refined fait petre employed in the operation funk the fpirit in the thermometer but three degrees and a half below the fixed point.

Of the fait petre he ufed, the unrefined makes the fpirit fink confide rably lower ; the caufe of which is, that the rough fait petre contains a large quantity of common, or fea fait ; and this being able to caufe a greater degree of cold than the fait it is mixed with, exerts itfelf with it, and carries it to a greater degree of coldnefs: whereas in the refining fait petre, this fea fait is thrown out, and confequently the nitre becom- ing purer, acts only on its own principle, and caufes a lefs degree of cold, fuch as is its appropriated one. Two parts of common fait being mixed with three parts of powder'd ice in very hot weather, the fpirit in the thermo- meter immediately defcended fifteen degrees, which is half a degree lower than it would have defcended in the fevereft cold of the year 1709. Mr. Reaumur after this experimented the falts all round, and tried with great regularity and exaclnefs, what was the degree of cold occafioned by each in a given dofe. Among the neutral falts, none produced a greater de- gree of cold than the common fea fait. Among the alkalies,

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fal armoniac, though generally efteemed fo very powerful a one on thefe occafions, funk the thermometer only to thir- teen degrees. Pot aihes funk it juft as low as well refined fait petre. Thus by trials of the feveral falts, the proper decree of cold producible from each is eafily ascertained, and tables may be made of the numbers. After which, in the defcri- bing any degree of cold in a particular feafon, it will be a much better way of expreffing it, to fay it was equal to that produced by fuch or fuch a fait, than to name it by the de- grees of a thermometer.

For the common ufes of the table, the ice required is not ex- pected to be very hard, or fuch as is produced by long conti j nuance of violent cold : it is rather defired to be like fnow. Salt petre, which is no very powerful freezer, is therefore more fit for the purpofe than a more potent fait. It is not required that the congelations fliould be very fuddenly made ; but its retaining its form as long as may be when made, is a thing of great importance to the dealer in thefe things ; nor is the price of the falts, which are to be ufed for this purpofe, a matter of indifference.

If it be defired to have ices very hard and firm, and very fud- denly prepared, then fea fait is of all others moft to be chofen for the operation. The ices thus made will be very hard, but they will keep only a very little time without running. Pot allies afford an ice of about the hardnefs that is ufually requi- red. This forms indeed very flowly, but then it wdl prcferva itfelf a long time. And there is another fubftance which per- forms the bufmefs very nearly in the fame manner with the pot aihes, and that on the fame principle : this is a very cheap and fimple one, being no other than common wood afhes ; but for this purpofe the wood, which is burnt, ought to be frefh. 6

The ftrong acid fpirits of the neutral falts a3 much more powerfully in thefe congelations than the falts themfelves, or indeed than any fimple fait can do. Thus fpirit of nitre mix- ed with twice its quantity of powder'd ice, immediately finks the fpirit in the thermometer to nineteen degrees ; that is, it produced a cold of four degrees greater than that obtained by means of fea fait, the moft powerful of all the falts in ma- king artificial cold. A much greater degree of cold may be given to this mixture by piling it round with more ice mixed with fea fait. This gives a redoubled cold, and on the trial the thermometer was found to fink to twenty-four degrees ; that is, a degree of cold was thus artificially produced, which was to the greateft known natural cold, that of the fevere win- ter in 1709, as twelve to feven, or thereabouts. If this whole matter be covered with a frefli mixture of fpirit of nitre and ice, a yet greater degree of cold is produced, and fo on ; the cold being by this method of frefh additions to be in- creafed almoft without bounds : but every addition, it is ob- ferved, gives a fmaller increale than the former. It is very remarkable in the acid fpirits, that though fea fait is fo greatly more powerful than nitre in fubftance in creatine cold, yet the fpirit of nitre is greatly ftronger than that of fea fait ; and another not lefs wonderful phienomenon is that of fpirit of wine, a liquor which is little other than a liquid fire, has as powerful an effedf. in congelations, or very nearly fo, as the fpirit of nitre itfelf. What but experiment could have brought people to imagine, that thefe two fo very different li- quors could have this property as it were in common. The mixture of any other matter with powder'd ice does not create a new cold by any other means than that of melting the ice it is mixed with. The moment of that melting is therefore the points of time in which the cold is ftron^eft of all, as after that the warmth of the external air cannot but be continually taking off from the new engender'd cold. It is plain from hence, that the quicker this melting is perform- ed, the harder the ice muft be, or the greater the degree of cold. It were much to be wifhed therefore, that the melt- ing could be inftantaneous, as in that cafe the particles of ice would all aft at one and the fame time on the matter to be congealed : and in order to this, it is neceffary that every par- ticle of ice fhould have a particle of fait ready to afl upon it. This requires that the ice and the fait fliould be both powder'd to a certain finenefs. Hence may be deduced a rule, which though not quite precife, yet may be fufficiently fo for the de- termining the proper proportion of the fait to be mixed with any determinate quantity of ice. We well know from ex- periment, how large a quantity of water is neceffary to melt a certain quantity of fait of any kind, and repeated experiments might bring the knowledge of the other folution to nearly as great a certainty. It would be well to try the whole carefully with fea fait ; and when the proportions of this were known, it would be no difficult matter from thefe to deduce the proper quantities of other falts, according to their known differences, in regard to the quantities of water neceffary to diflblve them. The feveral liquid fubftances which create a cold, in the fame manner as the dry falts on being mixed with ice, are much more fpeedy in their action than the falts; becaufe they im- mediately and much more intimately come into contafl with the particles of the ice, than the falts can. Of this nature are fpirit of nitre, fpirit of wine, &c. to produce the ex-

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