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proportion of the length ; the deficiency relative to the length is not so remark.
1 | 2 | 3 | 4 | 5 able here. Experiments 1 and 2, and Experiments 5 and 6, sbow the increase of
560 5350 3.5
56 5275 strength, by fastening the ends, to be in
4.5 the proportion of 2 to 3. The theory gives the proportion of 2 to 4. But a dif.
4600 3.75 ference in the manner of fixing may pro
4500 4.7 duce this deviation from the theory, which only supposed them to be held
4100 1 4.85 down at places beyond the props, as
3950 5.5 when a joist is held in the walls, and also rests on two pillars between the walls.
| 3625 | 5.83 We shall here give an abstract of M. Buf
3600 | 6.5 15 fon's experiments. He relates a great number, which he had prosecuted during 12 1100
S 100 3050 two years on small battens. He found
112 93 | 2925 8. that the odds of a single layer, or part of a layer, more or less, or even a different disposition of them, had such influences, Mr. George Smart, well known for his that he was obliged to abandon this me. practical knowledge of mechanics in althod, and to bave recourse to the largest most every department, says, that after beams that he was able to break. The fol. making many experiments on timber, and lowing table exhibits one series of expe. comparing them with those of Belidore, riments on bars of sound oak, clear of Buffon, &c. the differences were so great, knots, and four inches square. This is a than it would be wasting time to enume. specimen of all the rest. Column 1, is the rate them. He therefore mentions some length of the bar in feet clear between useful observations necessary to be known the supports. Column 2, is the weight of by all those mechanics who use timber; the bar (the second day after it was fello and points out some evident errors in a ed) in pounds. Two bars were tried of table of Belidore's, supposed to be the each length. Each of the first three pairs result of the best set of experiments ever consisted of two cuts of the same tree. produced in transverse strains. He tells The one next the root was always found us, that a bar of wood, thirty-six inches the heaviest, sti:fest, and strongest. In- long, and one inch square, supported at deed, M. Buffon says, that this was inva- the ends by two props, will break with a riably true, that the heaviest was always weight of 187 pounds on the middle, if it the strongest; and he recommends it as a is loose at the ends ; but if the ends are sure rule for the choice of timber. He firmly fixed, it will require 283 pounds to finds that this is always the case when break it. " This appeared to me,” says the timber has grown vigorously, forming Mr. Smart, “ so great an error, that I was very thick annual layers. But he also ob- induced to put little or no confidence in serves, that this is only during the ad. many of his experiments ; and, in consevances of the tree to maturity ; for the qucnce, I made two laths of fir, of the strength of the different circles approach. same dimensions, one with a strong shoul. es gradually to equality during the tree's der at each end, to prevent its bending, healthy growth, and then it decays in which having firmly fixed in a frame, it these parts in a contrary order. Our tool. carried a weight more than ten times makers assert the same thing with re. greater than that which was loose.” spect to beech ; yet a contrary opinion is The fibres of timber requiring so great very prevalent: and wood with a fine, a force to tear them asunder in a vertical that is, a small grain, is frequently prefer. direction, and being easily broken by a red. Perhaps no person has ever made transverse strain, when compared to that the trial with such minuteness as M. Buf- of a rope carrying nearly an equal weight fon, and much deference is thought to be in all directions, opens a wide field for due to his opinion. Column 3, is the num. useful experiments. All timber trees ber of pounds necessary for breaking the have their annual circles, or growths, tree in the course of a few minutes. Co. which vary greatly, according to the soil lumn 4, is the inches which it bent down and exposure to the sun. The north-east before breaking. Column 5, is the time side of the trees(being much smallerin the at which it broke.
grain than the other parts which are more exposed to the sun) is strongest for any As all beams take their weight horizoncolumn that has a weight to support in a taily, or on any transverse bearing, have vertical direction ; because its hard cir- their principal strain on the upper and cles, or tubes, are nearer each other, and lower surface, every workman ought to the area contains a greater quantity of guard against having sap in beams, bethem ; nor are they so liable to be com- cause, if they do not immediately decay, pressed by the weight, or to slide past they shrink, so as to let loose all the each other, as when they are at a greater framing, and soon cripple the building or distance. On the other hand, this part of machine: but on Mr. Smart's plan, the the tree is not fit for a transverse strain; sappy part of the wood is excluded from because the nearer the hard circles are what would cause its decay, and the timto each other, the easier the beam will ber, increased in quantity, is considerably break, there being so little space between more than the extra labour and expense. them, that one forms a fulcrum to break Timben trees, in law, are properly oak, the other upor ; but that part of a tree, ash, and elm. In some particular counthe tubes of wlich are at a greater dis. tries, by local custom, other trees being tance, or of a larger grain, is more elas commonly there made use of for building, tic, and requires a greater force to break are considered as timber. Of these, be. it; because the outside fibre on the con. Hurt of the freehold, larceny cannot vex side cannot snap till the next one is be committer; b::t if they be severed at pressed upon it, which forms the fulcrum one time, and carried away at another, to break it on. It is generally observed then the stealing of them is larceny. And in large timbers, such as masts, that the by several late statutes, the stealing of fracture is seldom on the convex, but them in the first instance is made felony, usually on the concave side; which is or incurs a pecuniary forfeiture. For the owing to the fibres on the concave side better preservation of roots, shrubs, and being more readily forced past each plants, it is enacted, by 6 George III. c. other, and those on the convex being 48, that every person convicted of damagso difficult to be torn asunder, that they ing, destroying, or carrying away any cannot snap, in consequence of the large. timber-tree or trees, or trees likely to ness of the segment of the circle they become timber, without consent of the describe when on the strain. The curve owner, &c. shall forfeit for the first ofdescribed by the inner layers of the fence not exceeding 201. with the charges wood being so large, and indeed little attending; and on non-payment shall be less than a straight line, cannot form a committed for not more than twelve, fulcrum to break the outer ones upon; nor less than six months ; for the second and as the convex side, or that on which offence, a sum not exceeding 301. and on the fibres are extended, ought to be al- non-payment shall be committed for not ways free from any mortise or incision on more than eighteen, and not less than the outside, the strength decreases as it twelve months; and for the third offence, approaches the centre. Mr. Smart has, is to be transported for seven years. All in a paper in the “Repertory,” given din oak, beech, chesnut, walnut, ash, elm, rections how to cut and join timber so as cedar, fir, asp, lime, sycamore, and birch to have the greatest strength, and to turn trees, shall be deemed and taken to be to the greatest advantage, of having the timber trees, within the true meaning best part of the tree in the place where and provision of this act. Persons conthe hardness and strength are most want. victed of plucking up, spoiling, or taking ed, ryz. in the corners which form the away any root, shrub, or plant, out of abutments; whereas the same tree, private cultivated ground, shall forfeit, for squared into a parallel beam, would have the first offence, any sum not exceeding been much smaller, and the soft or sappy 40s. with the charges; for the second of. parts of the wood exposed to the action fence, a sum not exceeding 51. with the of the air and moisture. In Aush fraining charges; and for the third offence, are it is observable, that the failure of all timn. to be transported for seven years. A ber in old buildings has commenced power is given to justices of the peace mich sooner than they otherwise would io put this in execution. have done, owing to the sappy wood be- TIME, a succession of phenomena in ing at the corners of the principal beains, the universe ; or a mode of duration, which soon decays, as its spongy quality marked by certain periods or measures, attracis the moisture ; whereas the heart, chiefly by the motion and revolution of especially of oak, will be as sound as the the sun. The idea of time, in the gene. first day it was used.
ral, Mr. Locke observes, we acquire by considering any part of infinite duration as from the motion of the heavenly bodies, set out by periodical measures: the idea without any other regard. of any particular time, or length of dura- TIME, civil, is the former time accomtion, as a day, an hour, &c. we acquire, modated to civil uses, and formed and first, by observing certain appearances at distinguished into years, months, days, regular, and seemingly, at equidistant &c. periods. Now, by being able to repeat T ime, in music, is an affection of sound, ihose lengths or measures of time as whereby we denominate it long or short, often as we will, we can imagine duration with regard to its continuance in the where nothing really endures or exists; same degree of time. and thus we imagine to-morrow, next T IN, in mineralogy, a genus of metals, year, &c. Some of the latter school-phi- of which there are three species: 1. losophers define time to be the duration Tin-pyrites; colour intermediate between of a thing, whose existence is neither steel-grey and brass-yellow; but usually without beginning nor end; by which more inclined to the first; it occurs mastime is distinguished from eternity. Time sive and disseminated: internally it is is distinguished into absolute and rela- glistening, sometimes shining, and seldoin tive. Absolute time, is time considered passing into splendent; its lustre is me. in itself, and without any relation to bo. iallic; it is brittle, and the specific gradies or their motions. This flows equal. vity is somewhere between 4.3 and 4.8. ly, i. e. never proceeds faster or slower, Before the blow-pipe it gives out a sul. but glides on in a constant, equable tenor. phureolis odour, and inelts easily, with. Relative time is the sensible measure of out being reduced, into a black scoria. It any duration, by means of motion. For, communicates a yellow or green colour since that equable fiux of time does not to borax. It consists of affect our senses, nor is any way imme. diately cognizable thereby, there is a ne.
Tin . . . . . . . 31 cessity for calling in the help of some
Copper . . . nearly equable motion to a sensible mea
Iron . . . . . sure, whereby we may determine its
Sulphur . . quantity by the correspondency of the
Earth . . . . . . parts of this with those of that. Hence, as we judge those times to be equal which
100 pass while a moving body, proceeding with an equable velocity, passes over equal spaces; so we judge those times to
It is found at Wheal-rock and St. Agbe equal, which Aow while the sun, moon,
nes in Cornwall, wbere it occurs in a vein and other luminaries, perform their revo.
about nine feet wide, accompanied with lutions, which, to our senses, are equal. But since the flux of time cannot be ac.
copper pyrites and brown blende.
2. Tin-stone, which is hard, brittle, and celerated, nor retarded, whereas all bo.
very heavy, the specific gravity being dies move sometimes faster and some. times slower, and there is, perhaps, no
from 5.8 to 6.9 or 7. Before the blowperfectly equable motion in all nature,
pipe it decrepitates, becomes paler, and,
where it rests on the charcoal, is reduced. it appears hence to follow, that absolute time should be something truly and real
When roasted, it is converted into a grey ly distinct from motion. But, according
oxide. A specimen, analysed by Klato Lucretius:
proth, contained “ Time, of itself, is nothing, but from
Tin . . . . . . 77.50
Iron . . thought
. . . . 0.25
Oxygen Receives its rise; by labouring fancy
. . . . 21.50' wrought
Silica . . . . From things consider'd, whilst we think on some
100.00 As present, some as past, or yet to come. No thought can think on time, that's still contest,
It occurs only in primitive rocks, as But thinks on things in motion, or at granite, kneiss, mica-slate, and clay-slate, rest."
and it is said to be the oldest of all the me
tals. It occurs either disseminated in the TOE, astronomical, is that taken purely rock, or in beds of reins. It is (isually
accompanied with quartz, mica, &c. and ists under a variety of forms. It is gene. is also found in great quantities in alluvial rally found crystallized. The sulphuret land. The greater part of the English, of tin is of a pale, or dark grey colour, much of the Spanish, and the greater pro- and, when pure, has some resemblance portion of that from India, occurs in that to an ore of silver. To obtain the metal situation.
from its ores, they are first roasted, and Tin is not found in many countries; then treated with a flux, to reduce the but where it exists at all, it is in very metal. After the ore is roasted, it fuses considerable quantities. In Europe there readily with three times its weight of are only three tin districts: the first is black Aux, and a little decrepitated mu. in Saxony and Bohemia ; the second in riate of soila. In the humid way, native Cornwall; and the third is that of Galli. tin may be dissolved in nitric acid, which cia, on the borders of Portugal. It is readily oxidates, and reduces it to the found in many parts of Asia, and in South state of white powder, which is an oxide America. It is worked as an ore of tin, of tin ; and if it contain iron and copper, and from it all the tin of commerce is ob. these two metals remain in the solution. tained. Its name is derived from the Tin is of a white colour, nearly as bril. quantity of tin which it affords, and its liant as silver. The specific gravity of unmetallic aspect.
tin is nearly 7.3. It is one of the softest 3. Cornish tin-ore, or wood-tin; which, of the metals. It is extremely flexible, like the last, is very heavy ; before the and so malleable, that it can be easily blow-pipe it is infusible; it consists of beaten out in plates to be part of an about 63 parts of tin, with iron and
inch, which is the thickness of tinfoil. It arsenic. It has hitherto been found only has little elasticity or tenacity. A wire in Cornwall, and there in alluvial land. It of this metal, about one-tenth of an inch is very like brown hematite, from which in diameter, supports a weight of about it is distinguished by its colour, its rolled thirty pounds, without breaking. Tin is pieces, greater hardness, and higher spe- susceptible of very considerable expan. cific gravity. We now turn to tin, in a sion, by means of caloric, and on this ac. chemical view.
count it has been proposed to employ it Tin is a metal of a silver white colour, as a pyrometer. 1'in is one of the most very ductile and malleable, gives out, fusible of the metals, and melts at the while bending, a crackling noise, is fusi. temperature of 442°; but it requires a ble at a heat much less than that of igni. very high temperature to raise it in va. tion, is soluble in muriatic acid, and, by pour. If it be allowed to cool slowly, dilute nitric acid, is rapidly converted in- and when the surface becomes solid by to a white oxide. Tin has been known pouring out part of the liquid metal, from the earliest ages. It was much em crystals are formed, composed of a great ployed by the Egyptians in the arts and number of small needies. Tin is a good by the Greeks as an alloy with other me- conductor of electricity. It possesses a tals. Pliny speaks of it under the name peculiar, odour, which is communicated to of white lead, as a metal well known in the hands by friction. It has also a per. the arts, and even applied in the fabrica. ceptible taste. When this metal is ex. tion of many ornaments of luxury. He posed to the air, it is soon tarnished, and ascribes to the Gauls the invention of the assumes a greyish-white colour; but it art of tinning, or covering other metals undergoes no further change. When it with a thin coat of tin. The alchemists is melted in an open vessel, it is soon cowere much employed in their researches vered with a greyish pellicle, which is concerning tin, and gave it the name of the commencement of the oxydation of Jupiter, froin which the salts, or prepara- the metal. When this pellicle is remov. tions of tin, were called jovial. Since ed, another forms, and so on successively, their time, the nature and properties of till the whole is oxydated. By continuing tin have been particularly investigated by the heat, and by agitation, the process many chemists, and it has proved the goes on more rapidly, and the metal is subject of some important discoveries in converted into a whitish powder. This chemical science. .Tin exists in nature oxide contains about twenty parts of oxyin three different states. 1. It is found gen in 100 of the metal. With the addinative ; 2. In the state of oxide ; and, 3. tion of lead, to promote the oxyciation, In that of sulphurated oxide. Native tin this oxide is the putty of tin. It contains is in brilliant plates, or regularly crystal about two parts of oxide of lead, and one lized. The native oxide of tin, which is part of oxide of tin. But when tin is the most common ore of this metal, ex. strongly heated, it is converted into a fine
white oxide, which, during the process, black mass, which is sulphuret of tin. This gives out a vivid white flame. This oxide compound, which is a sulphurated oxide is condensed in the cold, and crystallizes of tin, was formerly distinguished by the in shinning, transparent needles.
name of aurum, musivum, musicum, or Tin combines with two proportions of mosaicum. The component parts of this oxygen, thus forming two oxides. The sulphurated oxide of tin are, yellow oxide, which has the smaller pro. portion of oxygen, may be prepared by
Oxide of tin .... 60 dissolving tin in nitric acid diluted with
Sulphur ..... 40 water, without the aid of heat. By precipitating the oxide with pure potash, it
100 is obtained in the form of a yellowish powder. Its component parts are,
Tin enters into combination with many
of the metals, and forms alloys with Oxygen . . . . . 20
them, some of which are of great import. Tin . . . . . . . 80
ance. It also combines with acids, and
forms salts. 100
Of the alloys, the most important is that of tin and copper, with some other addi.
tions, which forms bronze,bell-metal, gpe. By dissolving tin in concentrated nitric culum metal, &c. The alloy of tin and acid, with the assistance of heat, the lead, in equal parts, forms plumbers' solwhole is converted with effervescence der. The alloy of tin, lead, and bismuth, into a white powder, which falls to the in the proportions of 3, 5, and 8, forms a bottom of the vessel. The compotent compound that melts in a heat somewhat parts of this oxide are 28 oxygen, and 72 less than that of boiling water. The amalof tin.
gam of mercury with tin is used in silverPhosphorus combines very readily with ing of mirrors. Pewter is an alloy of tin, by projecting bits of phosphorus on tin and lead, which was formerly very melted tin in a crucible. A phosphuret of much used, more so than any other me. tin is thus obtained, which crystallizes on tallic alloy, being the common material cooling. This compound is of a silvery for plates, disbes, and other domestic white colour, may be cut with a knife, utensils. Its use now is almost universaland extended under the hammer, but ly superseded by pottery, which is lightsoon separates into plates. Sulphur com- er, more readily kept clean, and much bines very readily with tin, by adding cheaper, though certainly less durable, the sulphur to the metal while in a state on account of the brittleness of the latter. of fusion. This compound forms a grey The name of pewter has been given to ish or bluish matter, which has a metallic any malleable white alloy, into which tin lastre, a lamellated structure, and crys- largely enters; and its composition is so tallizes in cubes, or in octahedrons. It is various, that bardly any two manufacturdecomposed by acids with effervescence. ers employ precisely the same ingreThe component parts are, according to dients, and the same proportions. The Bergman,
finest kind of pewter contains no lead
whatever, but consists of tin with a small * Sulphur ... . 20
alloy of antimony, and sometimes a little
copper, and in all the superior kinds of 100
pewter, the tin forms by far the greater part of the mixture. Pewter may be used
for vessels containing wine, and even viIf equal parts of oxide of tin and sul. negar, provided there be from 80 to 82 phur be fused together in a retort, sul parts of tin in the alloy, without the phurous acid, and some sulphur, are dis- smallest danger; hence its use as a meaengaged, and there remains in the vessel sure. The specific gravity of a mixture a compound of a brilliant, golden colour of tin and lead is less than the mean spe. It crystallizes in six-sided plates. It is not cific gravity of the two metals separate. acted on by the acids. When it is strongly ly. beated it gives out sulphurous acid and Tin is much used, particularly in the sulpbur, and there remains behind a state of very thin leayes: it is then called