Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/650

 T I N

The Dutch, who have Timber about their fiuices, and other buildings upon the water, more expofed to the injuries of wet and weather than any other that is known ; have a way of preferving it, by coating it over with a mixture of pitch and tar, which they fmear over the whole furface ; and immedi- ately, while it is moift, they throw on it as much fand and powder of cockle -fhells as it will retain. Thus it is coated over with a rough cruft which will defend it from all kinds of injuries. See the article Sulphur.

Green Timber is apt to fplit and cleave in feveral places, after it is wrought into form. Workmen have different methods of remedying this deformity, for which fee the article Clefts.

Felling of Timber. See the article Felling.

Hardening of T 'im_ber. See the articleHARDENiNG of Timber.

TiMBER-Lode, in our old writers, a fervice by which tenants were to carry Timber from the woods to the lord's houfe. Blount,

Meafuring of Timaer, To meafure round Timber without the help of inftruments : let the mean circumference be found in feet, and decimals of a foot; fquare it, multiply this fquare by the deci- mal 0.079577 and the product by the length. For inftance, let the mean circumference of a tree be 10.3 feet, and the length 24 feet; then 10.3X 10.3X0. 079577 x 24= 202.615 = the num- ber of cubical feet in the tree. The foundation of this rule is. that, when the circumference of a circle is 1, the area is O.0795774715, and that the areas of circles are as the fquares of their circumferences. Treat. Pract. Geom. p. 150. The common way ufed by artificers for meafuring round Tim- her, mentioned in the Cyclopaedia, differs much from this rule. One fourth part of the circumference or girt, is by them reck- oned the fide of a fquare, whofe area is equal to that of the fedtion of the tree ; they therefore fquare the girt, and then multiply by the length of the tree. According to this me- thod the tree of the laft example, would only be computed at 159,13 cubical feet.

TIME (Cj't-/.J — Time, in the manege, is fometimes taken for thi motion of a horfe, that obferyes meafure and juftnefs in perform ing a manege; and fometimes itfignifies the interval between two of his motions. In the manege of aftep and a leap, the horfe makes by turns a corvet between two caprioles ; and in that cafe the corvet is one Time that prepares the horfe for the caprioles The Times obferved in making a ftop, are nothing but fo many falcades.

Time alfo Ognifies the effecf of one of the aids, thus, we fay, a good horfeman difpofes his horfe for the effects of the heel, by beginning with one Time of the legs, and never runs pre- cipitately upon his Times.

TIMOROSO, in the Italian mufic, intimates that the fong is to be played or fung, in fuch a manner as to exprefs an awe or dread, either to fhew refpedt, or to reprefent fear.

TIMOROUS, in the manege. See the articles Starting, Skittish, t-fc.

TIN (Cyd.) — The combinations and feparations of metals, are fubjeefs that have employed the thoughts of the moft ac- curate chemifts in all ages ; yet new difcoveries are ftill to be made, and in thefe experiments as well as in many others, we are by no means yet arrived at the utmoft perfection. Mr. Grofle in the memoirs of the academy of fciences of Paris, has delivered a method he had invented of feparating Tin from lead or filver.

The advantages arifmg from the mixtures of different metals, are very numerous and of many different kinds ; to this we owe the metal ufed for bronzes, for bells, for reflecting mirrors ufed in opticks, and a multitude of the like matters; a mixture of this kind makes brafs of copper, a little copper in the fame manner, gives filver a hardnefs that greatly adds to its utility, and gives hardnefs and a more pleafing colour to gold ; a" little copper or antimony give Tin a hardnefs, and render it more fo- norous : and a multitude of advantages befides might be enu- merated. But there is no lefs neceflity and advantage alfo in the feparating metals, fometimes when they have been joined by art, or are found united by nature : in thefe cafes fometimes both the metals are preferved, fometimes the bafer or lefs valuable is deltroyed.

Of thefe feparations of metals fome are very eafy ; lead and mer- cury are feparated from gold and filver by heat alone, and fo are antimony from gold, or zink from copper. On the other hand there are fome feparations which cannot be effected without great trouble; of this kind are the mixtures of Tin with lead and with filver. It is not common to mix filver and Tin together on any occafion; but they are fometimes found mixed, and give the refiners great trouble ; and even the chemifts, who have often mixt Tin with filver to increafe it, have always found it very difficult to feparate it again.

Mr. Grofle happened to be prefent at the melting fome filver, which plainly indicating that it contained fome other metal, in the refining he ordered the workman to examine the lead which he ufed, and found that there W3S 27a among it. The fcorise of the metal, which contained with the Tin a large quantity of filver, had on thefe occafions been ufed to be fold to the bell-founders, to the great lofs of the proprietor of the metal. Some indeed had advifed different methods of reco- vering the metal from them, but without fuccefs. It was on thefe fcorize that Mr. Grofle tried his experiment j it feemed

TIN

to him that one great ftep toward the feparation of the filver, was the haftening the calcination of the Tin, and with this view he tried a mixture of charcoal, falt-petre, and earth, which he put together into the copel with the fcorise. It is eafy to fee that a detonation would happen from this, and this muft greatly add to the force of the fire, in ailing upon the fcorise, while the ferrugineous matter well known to be contained in the charcoal mixed itfelf with the Tin, and muft greatly accelerate its calcination, divide its parts, and give the fire a new action over it. The confequenceof this perfectly anfwered expectation, and recovered a large quantity of filver from the fcoriae, in which the Tin had before held it firmly imbodied ; repeated experiments proved the truth of this ob- fervation, and it was found to be eafy by this means at any time to feparate filver from Tin, or to purify filver without lofs, by means of lead in which Tin has accidentally been em- bodied. The common method ufed by the plumbers to fe- paratetheir folder from old leaden pipes, fifr. might fecm an eafy way of feparating Tin from lead, but this is not truly the cafe; the Tin in this inftance not being feparated from the lead, but only a mixture of Tin and lead, which had been employed as folder is feparated from fimple lead, which had been foldcred with it. The method of making this feparation, is only by melting the folder off from the fimple lead by a fire not ftrong enough to melt the lead Ltfelf.

The fcorise in which Tin is mixed with filver, are com- pofed of Tin half calcined, and run into an opake vitrified fub- ftance, which forms a fort of net- work, in which the filver is confined in extremely fmal! particles. If this is thrown into aqua fortis, the whole is diflblved : but then it requires a very ftrong fire to imake the Tin lofe its metallic form ; finally if the whole is finely powdered and then put into this menftruum, the filver only is taken up or diflblved, the Tin re- maining untouched at the bottom of the veflel. The fame gentleman found alfo a method of feparating Tin from filver, by means of corrofive fublimate of mercury. To conceive the manner in which this feparation is effected, a piece of fine Tin need only be caft into a folution of fubft- mate; in which cafe the acid of the fea-falt is feen to leave the mercury in order to fix upon the Tin. And, according to the fame principle, if fublimate corrofive be added to a mixture of Tin and filver, the fame effect is pro- duced, the acid affixes itfelf to the Tin, and makes with it a butyrum jcviale or butter of Tin, the mercury becomes difli- pated in the mean time by the action of the fire, and the fil- ver remains pure and alone ; but in this experiment, if too much corrofive fublimate be added, there is danger of lofing fome of the filver ; fince the abundant acid will prey upon and carry off a part of that metal, making a fort of luna cornea which difllpates itfelf in the air, or if the operation be performed inaclofe velfel, a butyrum lunare.

Gold may alio be purified from Tin in this manner, and in this there is no rifk oi lofs, fince the acid which takes up the Tin has not the leaft power over that metal : In all thefe pro- ceffes, however, the operator muft avoid the fumes ifluing from the crucible, for they are very dangerous. Thefe methods of feparating Tin from filver are very certain and infallible, but they are too expenfive to be employed in common, and in larger works.

The feparating Tin from lead to be employed in the refining of filver is a matter of great importance ; and this may be done in the following manner : Melt the lead, and when in fu- fion throw into it a quantity of filings of iron, then increafe the fire to a confiderable degree, and the furface of the me- tal will be covered with a fort of fcurn, which is no other than the iron and Tin. At this time there Ihould be a lit- tle alkali fait thrown in, and by this means the fcorije readily feparate themfelves, and the pure lead remains in form of a regulus at the bottom. The fame method may be ufed to fe- parate Tin from fiiver in the larger way, but it will be ne- ceflary for this purpofe to add fome lead, fince otherwife the fufion will be very flow and difficult, and the Tin will cal- cine without feparating from the filver. This is a very eafy and very cheap method, and will obviate moft of the mif- chiefs which happen to the refiners, of which they would have much lefs frequent reafon to complain, if they nicely ex- amined the lead they were to employ. But if gold or filver be mixed with Tin, the fhortefl method in fmall quantities is to calcine the whole very brifkty, and in order to compleat the vitrification and feparation of the Tin, to caft in a little glafs of lead, which will immediately join itfelf with it and carry it off from the mafs.

It may feem Angular that iron being one of the hardeft of the metals to melt, and Tin being of all the eafieft, they ihould fo readily and eafily unite in thefe experiments; but this feems to be the refult of one of thofe natural and unexpected alliances which accident frcquentlydifcovers to us in bodies. There is one con- jecture, however, that may be worthy a place in this refearch, which is, that all Tin or & contains a quantity of arfenic, and it is well kuown that iron very readily mixes with arfenic, and is employed to feparate the arfenic from other ores, and a regulus may be formed of arfenic and iron, It is eafy to fuppofe that Tin is in its metalline form, not wholly diverted of the arfenic it contained when in the ore, and if this be al-.

lowed,