Page:Cyclopaedia, Chambers - Volume 2.djvu/593

 REF

c#o

REF

This done, the Allies and other Impurities are blown from off the Top of the Metal, till it appear as clear as a Looking- Glafs, and then an Ounce of Borax broke in Pieces is thrown in.

Laftly, the Crucible being cover'd up again, they give it the kit Fire; after which 'tis caft into Ingots ; which are found ele- ven Penny- Weights, and fixteen Grains fine.

To recover the Silver that may be left in the Faces, or Sco- ria, they pound them, and give them repeated Lotions in frefh Waters. See Lavadero.

Refining of Copper, is only perform'd by giving the mineral Matter feveral Lotions before the melting it ; and then giving it feveral repeated Fulions. See Copper.

Refining of Tin is perform'd much after the fame Manner as that of Copper. See Tin.

Though, we may diftinguifh two Kinds of finenefs of this Me- tal: The one arifing frotrfits Fufion; that Tin taken firft out of the Coppers wherein it is melted, being always purer than that towards the Bottom.

The other Kind of finenefs is that given the Tin by adding fome other Metal or Mineral to it, to render it more founding, as well as more bright : Such is Tin of Antimony, Pewter, &c. See Pewter, t&c.

Refining of Iron, begins likewife by the melting it. See Iron and Iron-Works.

The greater Degree of Fuflon the Mineral has, the more the Metal is purified : But this firft Fufion is not fufficient. — To ren- der the Iron malleable, and fit it to endute the File, it muft be meited afecond time; then forged or beaten a long time with huge heavy Hammers, wrought by the Water ; then heated in the Fire, and at laft reduced on the Anvil, into Bars of feveral Thick- neffes. See Forging.

The more the Iron is heated in the Fire ; and the more 'tis beaten, whether hot or cold, the finer it becomes. See Iron.

Steel is only Iron refined to a great Degree by heating it, with fome other Ingredients which clofe up the Pores, and foften the Grain thereof. See Steel.

Refining of Lead, is perform'd like that of mod: other im- pettect Metals, by frequent Meltings, ftill fcumming it e're it be cold, and calling in Tallow, and otherKinds of Fat.

They alfo make Allays of Lead ; not to refine it, but to fee if it be pure, and without Mixture of any other Metal. See Lead.

Refining of Sugar.— The Operation is begun by feveral ftrong Lixiviums or Lyes of Lime-Water and Eggs, Shells and all, mix'd and beaten together.

This firft Renting is perform'd in the Caribees and other Places where the Sugar-Canes are cultivated; and only ferves for the brown or coarfer Sugars.

When thefe arc imported into Europe, the Sugar-Bakers take them up, and refine them further, by a fecond Operation, or rather a Repetition ot the firft.

To render the Sugar very fine, fit for Confections, they ufu- ally give it a third Refining; wherein they only ufe the Whites of Eggs, and their Shells beaten together, and thrown into the melt- ed Sugar; which is call'd clarifying the Sugar. See Sugar.

Refining of Salt-petre.—The Salt being put in an Earthen or Iron Veflel, as much Spring-Water is pour'd on it as fuffices to diffolve it. The VefTel is then put over a gentle Fire; and as foon as the Water begins to boil, Alumn-Powder is thrown into it : The Proportion is, one Pound of Alumn to 128 Pound of Salt-petre ; and a little Vinegar is added. As it boils, the Scum is to be taken off; and thus is it refined. See Salt-petre.

For the Refining of other Matters, as Camphor, Vermillion, Sul- phur, Lapis, Salt, Borax, &c. See Camphor, Vermillion, Sulphur, Salt, drc.

REFLECTING Telefiope, j REFLECTING MknfiopeX. REFLECTING Dial, i

/■Telescope. See } Microscope. (.Dial.

REFLECTION, or Reflexion, in Mechanicks, the re- turn, or regreffive Motion of a Moveable occafioned by the Refiftance of a Body, which hindered its purfuing its former Direction. See Motion, Resistence, <&c.

Tis controverted, whether there be any, Moments Reft or Interval between the Incidence and the Refleclion ? For the Af- firmative, ftand the Peripatetics, and all who conceive the re- flecled Motion to be different from the Incident one of the fame Body.— The Motion of Incidence, according to thefe Authors, is wholly loft and deftroyed by the Refiftence of the Obftacle ftruck againft ; and the moveable is thus render'd abfolutely qui- efcent in the Point of Contact ; till a new Motion ot Reflexion is produced therein, from a contrary Caufe.

The Cartefans affert the Negative ; abfolutely denying any Reft at all between the Incidence and Refleclion: Urging, that if the Motion were once deftroyed, though but for a Moment, there would be nothing to excite it again; but the Body would per- fevere in that new State, as much as if it had been at Reft a thoufand Years. See Rest and Lain of Nature. • Accordingly, Rohault, and others, define Refleclion to be no other than a Change of Determination; or a Continuation of the for- mer Motion in a new Direction. See Determination,

&c.

As, fay they, a Pendulum, when arrived at itsgteateftSweep, does not flop ; fo a hard Body, ftriking on another hard one, does not reft, but purfues its Motion the contrary Way, accord- ing to the eftablillied Law of Nature ; and this trom the imme- diate Influence or Impulfe of the Caufe that firft moved it.— But this Doctrine is now generally let afide.

Refleclion is conceiv'd by the lateft and beft Authors, as a Mo- tion peculiar to elaftic Bodies, whereby, after ftriking on others which they cannot remove, they recede, or turn back, by' their elaftic Power. See Elastic Bodies.

On this Principle it is aflerted, that there may be, and is a Period of Reft between the Incidence and Refleclion ; fince the reflected Motion is t not a Continuation of the other, but a new Motion, arifing from a new Caufe or Principle, viz.. the Power of Elafticity. See Elasticity.

'Tis one of the great Laws of Refleclion, that the Angle a re- flecled Body makes with the Plane of the rebelling Obftacle, is e- qual to that wherein it ftruck on that Obftacle. S'ee Angle and Incidence.

For tlx feveral Laws of Motion obferisedm the Reflection of Bodies, fee the Article Percussion.

Reflection of the Rays of Light, in Opticks, is a Motion of the Rays, whereby, after impinging on the folid Parts of Bo- dies, or rather, after a very near approach thereto, they recede or are driven therefrom. See Reflexibility.

The Refleclion of the Rays of Light from the Surfaces of Bo- dies, is the means whereby they become Vilibie. See Vision.

And the Difpofition of Bodies to reflect this or that Kind of Rays moft copioufly, is the Cauie of their being of this or that Colour. See Colour.

The Refleclion of Light from the Surfaces of Mirrors, makes the Subject of Catoptricks. See Catoptricks.

The Refleclion of L\ght,Sh- Ifaachas fhewn,isnot effected by the Rays ftriking 011 the very Parts of the Bodies; but by fome Power of the Body equally diffufed throughout its whole Surface, where- by it acts upon the Ray, by attracting or repelling it without any immediate Contact. See Ray.

This Power he fliews to be the fame whereby, in other Cir- cumftances, the Rays are refracted; and whereby they are at firft emitted from the lucid Body. See Light.

The Arguments he produces to this Purpoie are as follow.

1". Becaufe the Surfaces of poliilied Glaifes, which to the Eye appear fmooth, are yet in reality very rugged and uneven ; (po- lilning being nothing but the grating, fcratching, and breaking of the coarfer Protuberances, by means of Sand, Glafs, Putty, or TripolyJ. If the Rays of Light, therefore, were reflefled by ftriking on the folid Parts of the Glafs, the Reflections would ne- ver be fo accurate as we find they are ; but the Rays would even be as much fcatter'd by the mod polifh'd Glafs, as by the rough- eft.— It remains, therefore, a Problem, how Glafs' poliilied by fretting Subftances, can reflect Light fo regularly as it does; which Problem is fcarce otherwife to be folved than by fayum-, that the Reflexion of a Ray is effected, not by a tingle Point of the reflecling Body, but by fome Power of the whole Body, e- venly diffufed all over its Surface, and by which it acts on a Ray without immediate Contaft : For that the Parts of Bodies do aft upon Light at a Diftance, is already fhewn under the Article Inflection.

2 . If the Colours fcparated by a Ptifm placed at the Entrance of a Beam of Light into a darkened Room, be fucceflively caft on a fecond Prifm placed at a greater Diftance from the for- mer, in fuch manner as that they all tail alike, or with an equal obliquity upon it; the fecond Prifm may be fo inclined to the incident Rays, that thofe which ate of a blue Colour fhall be all refielted by it, and yet thofe of a red Colour pretty copioufly tranfmitted— Now, if the Reflexion were caufed by the Parts of the Air or Glafs, we would ask, why, at the fame Obliquity of Incidence, the blue fhould wholly impinge on thofe Parts fo as to be all reflecled, and yet the red find Pores enough to be in a great Meafure tranfmitted?

3 . Where two Glaifes touch one another, there is no fallible Reflexion, and yet we fee no Reafon why the Rays fhould not impinge on the Parts of the Giafs, as much when contiguous to other Glafs, as when contiguous to Air.

4°. When the top of a Water-Bubble, by the continual fub- fidmg and exhaling of the Water, grows very thin, there is fuch a little, and almoft infallible Quantity of Light replied from ir, that it appears intenfely black ; whereas round about that black Spot, where the Water is thicker, the Reflexion is lb ftrong as to make the Water fecm very white. — Nor is it only at the leaft thicknefs of thin Plates or Bubbles, that thete is no manifeft Re- fieclion,bat at many other tbickneffes, gradually greater and greater. For in one of our Author's Obfcrvations the Rays of the fame Colour were by turns ttanfinitted at one thicknefs, and reflecled at another thicknefs, foran indeterminate Number of Succellions: And yet in the Superficies of the thinned Body, where it is of one thicknefs, there are as many other Parts for Ravs to impinge one, as where it is of any other thicknefs.

5 . If red and and blue Rays, feparated by a Prifm, fall fucceflive- ly on a thin Plate of any pellucid Matter, whole thicknefs in- creafes in continual Proportion, (fuch as a Plate of Ait between two Glaffes, the one Plane and the other a little Convex) the

fame