TILTING OF STEEL

See Steel . Rees’s Cyclopædia contains an excellent article on this subject. TIN ( Etain , Fr.; Zinn , Germ.); in its pure state, has nearly the colour and lustre of silver. In hardne it is intermediate between gold and lead; it is very malleable, and may be laminated into foil le than the thousandth of an inch in thickne ; it has an unpleasant taste, and exhales on friction a peculiar odour; it is flexible in rods or straps of considerable strength, and emits in the act of bending a crackling sound, as if sandy particles were intermixed, called the creaking of tin. A small quantity of lead, or other metal, deprives it of this characteristic quality. Tin melts at 442° Fahr., and is very fixed in the fire at higher heats. Its specific gravity is 7·29. When heated to redne with free acce of air, it absorbs oxygen with rapidity, and changes first into a pulverulent gray protoxide, and by longer ignition, into a yellow-white powder, called putty of tin. This is the peroxide, consisting of 100 of metal + 27·2 of oxygen. Tin has been known from the most remote antiquity; being mentioned in the books of Moses. The Phœnicians carried on a lucrative trade in it with Spain and Cornwall. There are only two ores of tin; the peroxide, or tin-stone, and tin pyrites; the former of which alone has been found in sufficient abundance for metallurgic purposes. The external aspect of tin-stone has nothing very remarkable. It occurs sometimes in twin crystals; its lustre is adamantine; its colours are very various, as white, gray, yellow, red, brown, black; specific gravity 6·9 at least; which is, perhaps, its most striking feature. It does not melt by itself before the blowpipe; but is reducible in the smoky flame or on charcoal. It is insoluble in acids. It has somewhat of a greasy aspect; and strikes fire with steel. Tin-stone occurs di eminated in the antient rocks, particularly granite; also in beds and veins, in large irregular ma es, called stockwerks ; and in pebbles, an a emblage of which is called stream-works, where it occasionally takes a ligneous aspect, and is termed wood-tin . This ore has been found in few countries in a workable quantity. Its principal localities are, Cornwall, Bohemia, Saxony, in Europe; and Malacca and Banca, in Asia. The tin-mines of the Malay peninsula lie between the 10th and 6th degree of south latitude; and are most productive in the island of Junck-Ceylon, where they yield sometimes 800 tons per annum, which are sold at the rate of 48 l. each. The ores are found in large caves near the surface; and though actively mined for many centuries, still there is easy acce to the unexhausted parts. The mines in the island of Banca, to the east of Sumatra, discovered in 1710, are said to have furnished, in some years, nearly 3500 tons of tin. Small quantities occur in Gallic i a in Spain, in the department of Haute Vienne in France, and in the mountain chains of the Fichtel and Riesengebürge in Germany. The columnar pieces of pyramidal tin-ore from Mexico and Chile, are products of stream-works. Small groups of black twin crystals have been lately discovered in the albite rock of Chesterfield in Ma achusetts. The Cornish ores occur—1. in small strata or veins, or in ma es; 2. in stockwerks, or congeries of small veins; 3. in large veins; 4. di eminated in alluvial deposits. The stanniferous small veins, or thin flat ma es, though of small extent, are sometimes very numerous, interposed between certain rocks, parallel to their beds, and are commonly called tin-floors. The same name is occasionally given to stockwerks. In the mine of Bott a lack, a tin-floor has been found in the killas (primitive schistose rock), thirty-six fathoms below the level of the sea; it is about a foot and a half thick, and occupies the space between a principal vein and its ramification; but there seems to be no connexion between the floor and the great vein. 2. Stockwerks occur in granite and in the felspar porphyry, called in Cornwall, elvan . The most remarkable of these in the granite, is at the tin-mine of Carclase, near St. Austle . The works are carried on in the open air, in a friable granite, containing felspar disintegrated into kaolin , or china clay, which is traversed by a great many small veins, composed of tourmaline, quartz, and a little tin-stone, that form black delineations on the face of the light-gray granite. The thickne of these little veins rarely exceeds 6 inches, including the adhering solidified granite, and is occasionally much le . Some of them run nearly east and west, with an almost vertical dip; others, with the same direction, incline to the south at an angle with the horizon of 70 degrees. Stanniferous stockwerks are much more frequent in the elvan (porphyry); of which the mine of Trewidden-ball is a remarkable example. It is worked among flattened ma es of elvan , separated by strata of killas , which dip to the east-north-east at a considerable angle. The tin ore occurs in small veins, varying in thickne from half an inch to 8 or 9 inches, which are irregular, and so much interrupted, that it is difficult to determine either their direction or their inclination. 3. The large and proper metalliferous veins are not equally distributed over the surface of Cornwall and the adjoining part of Devons hire; but are grouped into three districts; namely, 1. In the south-west of Cornwall, beyond Truro; 2. In the neighbourhood of St. Austle; and 3. In the neighbourhood of Tav i stock in Devons hire. The first group is by far the richest, and the best explored. The formation most abundant in tin mines is principally granitic; whilst that of the copper mines is most frequently schistose or killas; though with numerous exceptions. The great tin veins are the most antient metalliferous veins in Cornwall; yet they are not all of one formation, but belong to two different systems. Their direction is, however, nearly the same, but some of them dip towards the north, and others towards the south. The first are older than the second; for in all the mines where these two sets of veins are a ociated, the one which dips to the north, cuts acro and throws out the one which dips to the south. See Mines , p. 835 . IMG:4147767755307473660_illo1242.png:Metal veins At Trevannance mines, the two systems of tin veins are both intersected by the oldest of the copper veins; indicating the prior existence of the tin veins. In fig. 1139. b , marks the first system of tin veins; c , the second; and d , the east and west copper veins. Some of these tin veins, as at Poldice, have been traced over an extent of two miles; and they vary in thickne from a small fraction of an inch to several feet, the average width being from 2 to 4 feet; though this does not continue uniform for any length, as these veins are subject to continual narrowings and expansions. The gangue is quartz, chlorite, tourmaline, and sometimes decomposed granite and fluor spar. 4. Alluvial tin ore, stream tin. —Peroxide of tin occurs di eminated both in the alluvium which covers the gentle slopes of the hills adjoining the rich tin-mines, and also in the alluvium which fills the valleys that wind round their base; but in these numerous deposits the tin-stone is rarely distributed in sufficient quantities to make it worth the working. The most important explorations of alluvial tin ore are grouped in the environs of St. Just and St. Austle; where they are called stream-works ; because water is the principal agent employed to separate the metallic oxide from the sand and gravel. IMG:4147767755307473660_illo1243a.png:Altenberg mine The tin mine of Altenberg, in Saxony ( fig. 1140. , which is a vertical projection in a plane pa ing from west to east,) is remarkable for a stockwerke, or interlaced ma of ramifying veins, which has been worked ever since the year 1458. The including rock is a primitive porphyry, superposed upon gnei ; becoming very quartzose as it approaches the lode. This is usually di eminated in minute particles, and accompanied with wolfram, copper and arsenical pyrites, fer oligiste , sulphuret of molybdenum, and bismuth, having gangues of lithomarge, fluor spar, mica, and felspar. The space which the ore occupies in the heart of the quartz, is a kind of dædal us, the former being often so dispersed among the latter as to seem to merge into it; whence it is called by the workmen zwitter , or ambiguous . In 1620, the mine was worked by 21 independent companies, in a most irregular manner, whereby it was damaged to a depth of 170 fathoms by a dreadful downfall of the roofs. This happened on a Sunday, providentially, when the pious miners were all at church. The depth of this aby , marked by the curved line b , b , b , is 66 fathoms; but the devastation is manifest to a depth of 95 fathoms below that curve, and 35 fathoms below the actual workings, represented at the bottom of the shaft under B . The parts excavated are shaded black in the figure. There are two ma es of ore, one under the shaft B , and another under the shaft C ; which at the levels 5 and 10 are in communication, but not at 6, 7. There is a direct descent from 8 to 9. The deposits are by no means in one vertical plane, but at a considerable horizontal distance from each other. A is the descending shaft; B is the extraction shaft, near the mouth of which there is a water-wheel; C is another extraction shaft, worked also by means of a water-wheel. A and C are furnished with ladders, but for B the ladders are placed in an acce ory shaft b′ ; under D , a shaft is sunk for pumping out the water, by means of an hydraulic wheel at D ; E is the gallery or drift for admitting the water which drives the wheels. This falls 300 feet, and ought to be applied to a water-pre ure engine, instead of the paddles of a wheel. At D , is the gallery of discharge for the waters, which serves also to ventilate the mine, being cut to the day, through 936 toises of syenitic porphyry and gnei . J , is a great vaulted excavation. The mine has 13 stages of galleries, of which 11 serve for extracting the ore; 1 is the mill-course; the rest are marked with the numbers 2, 3, 4, .; each having besides a characteristic German name. The rare mineral called topaz pycnite is found in this mine, above 10, between the shafts C and D . The only rule observed in taking ore from this mine, has been to work as much out of each of these levels as is po ible, without endangering the superincumbent or collateral galleries; on which account many pillars are constructed to support the roofs. The mine yields annually 1600 quintals (Leipzick) of tin, being four-fifths of the whole furnished by the district of Altenberg; to produce which, 400,000 quintals of ore are raised. 1000 parts of the rock yield 8 of concentrated schlich, equivalent to only 4 of metal; being only 1 in 250 parts. But the most extensive and productive stream-works, are those of Pentowan, near St. Austle. IMG:4147767755307473660_illo1243b.png:Pentowan mine Fig. 1141. represents a vertical section of the Pentowan mine, taken from the stream-work , Happy Union . A vast excavation, R , T , U , S , has been hollowed out in the open air, in quest of the alluvial tin ore T , which occurs here at an unusual depth, below the level of the strata R , S . Before getting at this deposit, several succe ive layers had to be sunk through; namely, 1, 2, 3; the gravel, containing in its middle a band of ochreous earth 2, or ferruginous clay; 4, a black peat, perfectly combustible, of a coarse texture, composed of reeds and woody fibres, cemented into a ma by a fine loam; 5, coarse sea-sand, mingled with marine shells; 6, a blackish marine mud, filled with shells. Below these the deposit of tin-stone occurs, including fragments of various size, of clay slate, flinty slate, quartz, iron ore, jasper; in a word, of all the rocks and gangues to be met with in the surrounding territory, with the exception of granite. Among these fragments there occur, in rounded particles, a coarse quartzose sand, and the tin-stone, commonly in small grains and crystals. Beneath the bed T , the clay slate occurs, called killas ( A , X , Y ), which supports all the deposits of more recent formation. The system of mining is very simple. The succe ive beds, whose thickne is shown in the figure, are visibly cut out into steps or platforms. By a level or gallery of efflux k , the waters flow into the bottom of the well l , m , which contains the drainage pumps; and these are put in action by a machine j , moved by a water-wheel. The extraction of the ore is effected by an inclined plane i , cut out of one of the sides of the excavation, at an angle of about 45 degrees. At the lower end of this sloping pathway there is a place of loading; and at its upper end h , a horse-gin, for alternately raising and lowering the two baskets of extraction on the pathway i .