T._A Dictionary of Arts, Manufactures and Mines containing a clear exposition of their principles and practice

TABBYING, or WATERING, is the process of giving stuffs a wavy appearance

with the calender.

TACAMAHAC, is a resin obtained from the _Fagura octandra_, a tree which

grows in Mexico and the West Indies. It occurs in yellowish pieces, of a

strong smell, and a bitterish aromatic taste. That from the island of

Madagascar has a greenish tint.

TAFFETY, is a light silk fabric, with a considerable lustre or gloss.

TAFIA, is a variety of rum.

TALC, is a mineral genus, which is divided into two species, the common

and the indurated. The first occurs massive, disseminated in plates,

imitative, or crystallized in small six-sided tables. It is splendent,

pearly, or semi-metallic, translucent, flexible, but not elastic. It

yields to the nail; spec. gray. 2·77. Before the blowpipe, it first

whitens, and then fuses into an enamel globule. It consists of--silica,

62; magnesia, 27; alumina, 1·5; oxide of iron, 3·5; water, 6. Klaproth

found 2-1/2 per cent. of potash in it. It is found in beds of clay-slate

and mica-slate, in Aberdeenshire, Banffshire, Perthshire, Salzburg, the

Tyrol, and St. Gothard. It is an ingredient in rouge for the toilette,

communicating softness to the skin. It gives the flesh polish to soft

alabaster figures, and is also used in porcelain paste.

The second species, or talc-slate, has a greenish-gray colour; is

massive, with tabular fragments, translucent on the edges, soft, with a

white streak; easily cut or broken, but is not flexible; and has a

greasy feel. It occurs in the same localities as the preceding. It is

employed in the porcelain and crayon manufactures; as also as a crayon

itself, by carpenters, tailors, and glaziers.

TALLOW (_Suif_, Fr.; _Talg_, Germ.); is the concrete fat of quadrupeds

and man. That of the ox consists of 76 parts of stearine, and 24 of

oleine; that of the sheep contains somewhat more stearine. See FAT and

STEARINE.

Tallow imported into the United Kingdom, in 1836, 1,186,364 cwts. 1 qr.

4 lbs.; in 1837, 1,308,734 cwts. 1 qr. 4 lbs. Retained for home

consumption, in 1836, 1,318,678 cwts. 1 qr. 25 lbs.; in 1837, 1,294,009

cwts. 2 qrs. 21 lbs. Duty received, in 1836, _£_208,284; in 1837,

_£_204,377.

TALLOW, PINEY. See PINEY TALLOW.

TAMPING, is a term used by miners to express the filling up of the hole

which they have bored in a rock, for the purpose of blasting it with

gunpowder. See MINES.

TAN, or TANNIC ACID. (_Tannin_, Fr.; _Gerbstoff_, Germ.) See its

preparation and properties described under GALLS.

The barks replete with this principle should be stripped with hatchets

and bills, from the trunk and branches of trees, not less than 30 years

of age, in spring, when their sap flows most freely. Trees are also

sometimes barked in autumn, and left standing, whereby they cease to

vegetate, and perish ere long; but afford, it is thought, a more compact

timber. This operation is, however, too troublesome to be generally

practised, and therefore the bark is commonly obtained from felled

trees; and it is richer in tannin the older they are. The bark mill is

described in Gregory’s _Mechanics_, and other similar works.

The following TABLE shows the quantity of extractive matter and tan in

100 parts of the several substances:--

+----------------------------------+--------+----------+-------------+

+----------------------------------+--------+----------+-------------+

|White inner bark of old oak | 72 | | 21 |

| Do. young oak | 77 | | |

| Do. Spanish chestnut | 63 | 30 | |

| Do. Leicester willow | 79 | | |

|Coloured or middle bark of oak | 19 | | |

| Do. Spanish chestnut | 14 | | |

| Do. Leicester willow | 16 | | |

|Entire bark of oak | 29 | | |

| Do. Spanish chestnut | 21 | | |

| Do. Leicester willow | 33 | 109 | |

| Do. Elm | 13 | 28 | |

|Sicilian sumach | 78 | 158 | |

|Malaga sumach | 79 | | |

|Souchong tea | 48 | | |

|Green tea | 41 | | |

|Bombay catechu | 261 | | |

|Bengal catechu | 231 | | |

|Nut-galls | 127 | | 46 |

|Bark of oak, cut in winter | -- | 30 | |

| Do. beech | -- | 31 | |

| Do. Elder | -- | 41 | |

| Do. Plum-tree | -- | 58 | |

|Bark of the trunk of Willow | -- | 52 | |

| Do. Sycamore | -- | 53 | 16 |

|Bark of Birch | -- | 54 | |

|Bark of Cherry-tree | -- | 59 | 24 |

| Do. Sallow | -- | 59 | |

| Do. Poplar | -- | 76 | |

| Do. Hazel | -- | 79 | |

| Do. Ash | -- | 82 | |

| Do. trunk of Span. chestnut | -- | 98 | |

| Do. Smooth oak | -- | 104 | |

| Do. Oak, cut in spring | -- | 108 | |

|Root of Tormentil | -- | | 46 |

|Cornus sanguinea of Canada | -- | | 44 |

|Bark of Alder | -- | | 36 |

| Do. Apricot | -- | | 32 |

| Do. Pomegranate | -- | | 32 |

| Do. Cornish cherry-tree | -- | | 19 |

| Do. Weeping willow | -- | | 16 |

| Do. Bohemian olive | -- | | 14 |

| Do. Tan shrub with myrtle leaves| -- | | 13 |

| Do. Virginian sumach | -- | | 10 |

| Do. Green oak | -- | | 10 |

| Do. Service-tree | -- | | 8 |

| Do. Rose chestnut of Amer. | -- | | 8 |

| Do. Rose chestnut | -- | | 6 |

| Do. Rose chestnut of Carolina | -- | | 6 |

| Do. Sumach of Carolina | -- | | 5 |

+----------------------------------+--------+----------+-------------+

TANNING (_Tanner_, Fr.; _Gärberei_, Germ.); is the art of converting

skin into LEATHER, which see. It has been ascertained, beyond a doubt,

that “the saturated infusions of astringent barks contain much less

extractive matter, in proportion to their tannin, than the weak

infusions; and when skin is quickly tanned (in the former), common

experience shows that it produces leather less durable than leather

slowly formed.”[66] The older tanners, who prided themselves on

producing a substantial article, were so much impressed with the

advantages of slowly impregnating skin with astringent matter, that they

employed no concentrated infusion (ooze) in their pits, but stratified

the skins with abundance of ground bark, and covered them with soft

water, knowing that its active principles are very soluble, and that, by

being gradually extracted, they would penetrate uniformly the whole of

the animal fibres, instead of acting chiefly upon the surface, and

making brittle leather, as the strong infusions never fail to do. In

fact, 100 pounds of skin, quickly tanned in a strong infusion of bark,

produce 137 of leather; while 100 pounds, slowly tanned in a weak

infusion, produce only 117-1/2. The additional 19-1/2 pounds weight in

the former case serve merely to swell the tanner’s bill, while they

deteriorate his leather, and cause it to contain much less of the

textile animal solid. Leather thus highly charged with tannin, is,

moreover, so spongy as to allow moisture to pass readily through its

pores, to the great discomfort and danger of persons who wear shoes made

of it. That the saving of time, and the increase of product, are

temptations strong enough to induce many modern tanners to steep their

skins in a succession of strong infusions of bark, is sufficiently

intelligible; but that any shoemaker should be so ignorant or so foolish

as to proclaim that his leather is made by a process so injurious to its

quality, is unaccountably stupid.

[66] Sir H. Davy, on the Operation of Astringent Vegetables in

Tanning.--_Phil. Trans._ 1803.

TANTALUM, is the rare metal; also called COLUMBIUM.

TAPESTRY, is an ornamental figured textile fabric of worsted or silk,

for lining the walls of apartments; of which the most famous is that of

the Gobelins Royal Manufactory, near Paris.

TAPIOCA, is a modification of starch, partially converted into gum, by

heating and stirring cassava upon iron plates. See CASSAVA and STARCH.

TAR (_Goudron_, Fr.; _Ther_, Germ.); is the viscid, brown-black,

resino-oleaginous compound, obtained by distilling wood in close

vessels, or in ovens of a peculiar construction. See CHARCOAL, PITCOAL,

COKING OF, and PYROLIGNOUS ACID. According to Reichenbach, tar contains

the peculiar proximate principles, _paraffine_, _eupion_, _creosote_,

_picamar_, _pittacal_, besides pyrogenous resin, or _pyretine_,

pyrogenous oil, or _pyroleine_, and vinegar. The resin, oil, and vinegar

are called empyreumatic, in common language.

Tar imported into the United Kingdom, in 1836, 9,797 lsts. 8 brls.; in

1837, 11,480 lsts. 1 brl. Retained for home consumption, in 1836, 9,639

lsts. 8 brls.; in 1837, 11,686 lsts. 8 brls. Duty received, in 1836,

_£_7,231; in 1837, _£_8,775.

TARRAS; see CEMENT, and MORTAR, HYDRAULIC.

TARTAR (_Tartre_, Fr.; _Weinstein_, Germ.); called also argal or argol;

is the crude bitartrate of potassa, which exists in the juice of the

grape, and is deposited from wines in their fermenting casks, being

precipitated in proportion as the alcohol is formed, in consequence of

its insolubility in that liquid. There are two sorts of argal known in

commerce, the white, and the red; the former, which is of a pale-pinkish

colour, is the crust let fall by white wines; the latter is a dark-red,

from red wines.

The crude tartar is purified, or converted into cream of tartar, at

Montpellier, by the following process:--

The argal having been ground under vertical mill-stones, and sifted, one

part of it is boiled with 15 of water, in conical copper kettles, tinned

on the inside. As soon as it is dissolved, 3-1/2 parts of ground

pipe-clay are introduced. The solution being well stirred, and then

settled, is drawn off into crystallizing vessels, to cool; the crystals

found concreted on the sides and bottom are picked out, washed with

water, and dried. The mother-water is employed upon a fresh portion of

argal. The crystals of the first crop are re-dissolved, re-crystallized,

and exposed upon stretched canvas to the sun and air, to be bleached.

The clay serves to abstract the colouring-matter. The crystals formed

upon the surface are the whitest, whence the name cream of tartar is

derived.

Purified tartar, the bitartrate of potassa, is thus obtained in hard

clusters of small colourless crystals, which, examined by a lens, are

seen to be transparent 4-sided prisms. It has no smell, but a feebly

acid taste; is unchangeable in the air, has a specific gravity of 1·953,

dissolves in 16 parts of boiling water, and in 200 parts at 60° F. It is

insoluble in alcohol. It consists of 24·956 potassa, 70·276 tartaric

acid, and 4·768 water. It affords, by dry distillation, pyrotartaric

acid, and an empyreumatic oil; while carbonate of potassa remains

associated with much charcoal in the retort, constituting black flux.

Tartar is used in dyeing, medicine, and for extracting--

TARTARIC ACID. (_Acide tartarique_, Fr.; _Weinsteinsäure_, Germ.) This

is prepared by adding gradually to a boiling-hot solution of 100 parts

of tartar, in a large copper boiler, 26 of chalk, made into a smooth pap

with water. A brisk effervescence ensues, by the disengagement of the

carbonic acid of the chalk, while its base combines with the acid excess

in the tartar, and forms an insoluble precipitate of tartrate of lime.

The supernatant liquor, which is a solution of neutral tartrate of

potassa, must be drawn off by a syphon, and decomposed by a solution of

chloride of calcium (muriate of lime). 28-1/2 parts of the dry chloride

are sufficient for 100 of tartar. The tartrate of lime, from both

processes, is to be washed with water, drained, and then subjected, in a

leaden cistern, to the action of 49 parts of sulphuric acid, previously

diluted with 8 times its weight of water: 100 of dry tartrate take 75 of

oil of vitriol. This mixture, after digestion for a few days, is

converted into sulphate of lime and tartaric acid. The latter is to be

separated from the former by decantation, filtration through canvas, and

edulcoration of the sulphate of lime upon the filter.

The clear acid is to be concentrated in leaden pans, by a moderate heat,

till it acquires the density of 40° B. (spec. grav. 1·38), and then it

is run off, clear from any sediment, into leaden or stoneware vessels,

which are set in a dry stove-room for it to crystallize. The crystals,

being re-dissolved and re-crystallized, become colourless 6-sided

prisms. In decomposing the tartrate of lime, a very slight excess of

sulphuric acid must be employed; because pure tartaric acid would

dissolve any tartrate of lime that may escape decomposition. Bone black,

previously freed from its carbonate and phosphate of lime, by muriatic

acid, is sometimes employed to blanch the coloured solutions of the

first crystals. Tartaric acid contains nearly 9 per cent. of combined

water. It is soluble in two parts of water at 60°, and in its own weight

of boiling water. In its dry state, as it exists in the tartrate of lime

or lead, it consists of 36·8 of carbon, 3 of hydrogen, and 60·2 of

oxygen. It is much employed in calico-printing, and for making sodaic

powders.

TARTRATES, are salts composed of tartaric acid, and oxidized bases, in

equivalent proportions.

TAWING, is the process of preparing the white skins of the sheep doe,

&c. See LEATHER.

TEA, _green_, contains 34·6 parts of tannin, 5·9 of gum, 5·7 of

vegetable albumine, 51·3 of ligneous fibre, with 2·5 of loss; and

_black_ tea contains 40·6 of tannin, 6·3 of gum, 6·4 of vegetable

albumine, 44·8 of ligneous fibre, with 2 of loss. The ashes

contain silica, carbonate of lime, magnesia, and chloride of

potassium.--_Frank._ Davy obtained 32·5 of extract from Souchong tea; of

which 10 were precipitated by gelatine. He found 8·5 only of tannin in

green tea. The latter chemist is most to be depended upon. Chemical

analysis has not yet discovered that principle in tea, to which its

exciting property is due.

_The Chinese method of making Black Tea in Upper Assam._[67]--In the

first place, the youngest and most tender leaves are gathered; but when

there are many hands and a great quantity of leaves to be collected, the

people employed nip off with the forefinger and thumb the fine end of

the branch with about four leaves on, and sometimes even more, if they

look tender. These are all brought to the place where they are to be

converted into tea; they are then put into a large, circular,

open-worked bamboo basket, having a rim all round, two fingers broad.

The leaves are thinly scattered in these baskets, and then placed in a

framework of bamboo, in all appearance like the side of an Indian hut

without grass, resting on posts, 2 feet from the ground, with an angle

of about 25°. The baskets with leaves are put in this frame to dry in

the sun, and are pushed up and brought down by a long bamboo with a

circular piece of wood at the end. The leaves are permitted to dry about

two hours, being occasionally turned; but the time required for this

process depends on the heat of the sun. When they begin to have a

slightly withered appearance, they are taken down and brought into the

house, where they are placed on a frame to cool for half an hour. They

are then put into smaller baskets of the same kind as the former, and

placed on a stand. People are now employed to soften the leaves still

more, by gently clapping them between their hands, with their fingers

and thumb extended, and tossing them up and letting them fall, for about

five or ten minutes. They are then again put on the frame during half an

hour, and brought down and clapped with the hands as before. This is

done three successive times, until the leaves become to the touch like

soft leather; the beating and putting away being said to give the tea

the black colour and bitter flavour. After this the tea is put into hot

cast-iron pans, which are fixed in a circular mud fireplace, so that the

flame cannot ascend round the pan to incommode the operator. This pan is

well heated by a straw or bamboo fire to a certain degree. About two

pounds of the leaves are then put into each hot pan, and spread in such

a manner that all the leaves may get the same degree of heat. They are

every now and then briskly turned with the naked hand, to prevent a leaf

from being burnt. When the leaves become inconveniently hot to the hand,

they are quickly taken out and delivered to another man with a

close-worked bamboo basket ready to receive them. A few leaves that may

have been left behind are smartly brushed out with a bamboo broom; all

this time a brisk fire is kept up under the pan. After the pan has been

used in this manner three or four times, a bucket of cold water is

thrown in, and a soft brickbat and bamboo broom used, to give it a good

scouring out; the water is thrown out of the pan by the brush on one

side, the pan itself being never taken off. The leaves, all hot on the

bamboo basket, are laid on a table that has a narrow rim on its back, to

prevent these baskets from slipping off when pushed against it. The two

pounds of hot leaves are now divided into two or three parcels, and

distributed to as many men, who stand up to the table with the leaves

right before them, and each placing his legs close together; the leaves

are next collected into a ball, which he gently grasps in his left hand,

with the thumb extended, the fingers close together, and the hand

resting on the little finger. The right hand must be extended in the

same manner as the left, but with the palm turned downwards, resting on

the top of the ball of tea leaves. Both hands are now employed to roll

and propel the ball along; the left hand pushing it on, and allowing it

to revolve as it moves; the right hand also pushes it forward, resting

on it with some force, and keeping it down to express the juice which

the leaves contain. The art lies here in giving the ball a circular

motion, and permitting it to turn under and in the hand two or three

whole revolutions, before the arms are extended to their full length,

and drawing the ball of leaves quickly back without leaving a leaf

behind, being rolled for about five minutes in this way. The ball of tea

leaves is from time to time gently and delicately opened with the

fingers, lifted as high as the face, and then allowed to fall again.

This is done two or three times, to separate the leaves; and afterwards

the basket with the leaves is lifted up as often, and receives a

circular shake to bring these towards the centre. The leaves are now

taken back to the hot pans, and spread out in them as before, being

again turned with the naked hand, and when hot taken out and rolled;

after which they are put into the drying basket, and spread on a sieve

which is in the centre of the basket, and the whole placed over a

charcoal fire. The fire is very nicely regulated; there must not be the

least smoke, and the charcoal should be well picked.

[67] By C. A. Bruce, superintendent of tea culture.

When the fire is lighted, it is fanned until it gets a fine red glare,

and the smoke is all gone off; being every now and then stirred and the

coals brought into the centre, so as to leave the outer edge low. When

the leaves are put into the drying basket, they are gently separated by

lifting them up with the fingers of both hands extended far apart, and

allowing them to fall down again; they are placed 3 or 4 inches deep on

the sieve, leaving a passage in the centre for the hot air to pass.

Before it is put over the fire, the drying basket receives a smart slap

with both hands in the act of lifting it up, which is done to shake down

any leaves that might otherwise drop through the sieve, or to prevent

them from falling into the fire and occasioning a smoke, which would

affect and spoil the tea. This slap on the basket is invariably applied

throughout the stages of the tea manufacture. There is always a large

basket underneath to receive the small leaves that fall, which are

afterwards collected, dried, and added to the other tea; in no case are

the baskets or sieves permitted to touch or remain on the ground, but

always laid on a receiver with three legs. After the leaves have been

half dried in the drying basket, and while they are still soft, they are

taken off the fire and put into large open-worked baskets, and then put

on the shelf, in order that the tea may improve in colour.

Next day the leaves are all sorted into large, middling, and small;

sometimes there are four sorts. All these, the Chinese informed me,

become so many different kinds of teas; the smallest leaves they called

Pha-ho, the second Pow-chong, the third Su-chong, and the fourth, or the

largest leaves, Toy-chong. After this assortment they are again put on

the sieve in the drying basket (taking great care not to mix the sorts),

and on the fire, as on the preceding day; but now very little more than

will cover the bottom of the sieve is put in at one time, the same care

of the fire is taken as before, and the same precaution of tapping the

drying basket every now and then. The tea is taken off the fire with the

nicest care, for fear of any particle of the tea falling into it.

Whenever the drying basket is taken off, it is put on the receiver, the

sieve in the drying basket taken out, the tea turned over, the sieve

replaced, the tap given, and the basket placed again over the fire. As

the tea becomes crisp, it is taken out and thrown into a large receiving

basket, until all the quantity on hand has become alike dried and crisp;

from which basket it is again removed into the drying basket, but now in

much larger quantities. It is then piled up eight and ten inches high on

the sieve in the drying basket; in the centre a small passage is left

for the hot air to ascend; the fire that was before bright and clear,

has now ashes thrown on it to deaden its effect, and the shakings that

have been collected are put on the top of all; the tap is given, and the

basket with the greatest care is put over the fire. Another basket is

placed over the whole, to throw back any heat that may ascend. Now and

then it is taken off, and put on the receiver; the hands, with the

fingers wide apart, are run down the sides of the basket to the sieve,

and the tea gently turned over, the passage in the centre again made,

&c., and the basket again placed on the fire. It is from time to time

examined, and when the leaves have become so crisp that they break by

the slightest pressure of the fingers, it is taken off, when the tea is

ready. All the different kinds of leaves underwent the same operation.

The tea is now little by little put into boxes, and first pressed down

with the hands and then with the feet (clean stockings having been

previously put on).

There is a small room inside of the tea-house, 7 cubits square and 5

high, having bamboos laid across on the top to support a net work of

bamboo, and the sides of the room smeared with mud to exclude the air.

When there is wet weather, and the leaves cannot be dried in the sun,

they are laid out on the top of this room, on the network, on an iron

pan, the same as is used to heat the leaves; some fire is put into it,

either of grass or bamboo, so that the flame may ascend high; the pan is

put on a square wooden frame, that has wooden rollers on its legs, and

pushed round and round this little room by one man, while another feeds

the fire, the leaves on the top being occasionally turned; when they are

a little withered, the fire is taken away, and the leaves brought down

and manufactured into tea, in the same manner as if it had been dried in

the sun. But this is not a good plan, and never had recourse to, if it

can possibly be avoided.

Tea imported into the United Kingdom, in 1836, 49,307,701 lbs.; in 1837,

36,765,735 lbs. Retained for home consumption, in 1836, 49,841,507 lbs.;

in 1837, 31,872 lbs. Duty received, in 1836, _£_4,728,600; in 1837,

_£_3,319,665.

TEASEL, the head of the thistle (_Dipsacus_), is employed to raise the

nap of cloth. See WOOLLEN MANUFACTURE.

TEETH. See BONES.

TELLURIUM, is a metal, too rare and high-priced to be used in the arts.

TERRA-COTTA, literally baked clay, is the name given to statues,

architectural decorations, figures, vases, &c., modelled or cast in a

paste made of pipe or potter’s clay and a fine-grained colourless sand,

from Ryegate, with pulverized potsherds, slowly dried in the air, and

afterwards fired to a stony hardness in a proper kiln. See STONE,

ARTIFICIAL.

TERRA DI SIENA, is a brown ferruginous ochre, employed in painting.

TESTS, are chemical reagents of any kind, which indicate, by special

characters, the nature of any substance, simple or compound. See ASSAY,

the several metals, acids, &c.

[Illustration: 1103 1104]

TEXTILE FABRICS. The first business of the weaver is to adapt those

parts of his loom which move the warp, to the formation of the various

kinds of ornamental figures which the cloth is intended to exhibit. This

subject is called the _draught_, drawing or reading in, and the cording

of looms. In every species of weaving, whether direct or cross, the

whole difference of pattern or effect is produced, either by the

succession in which the threads of warp are introduced into the

heddles, or by the succession in which those heddles are moved in the

working. The heddles being stretched between two shafts of wood, all the

heddles connected by the same shafts are called a leaf; and as the

operation of introducing the warp into any number of leaves is called

drawing a warp, the plan of succession is called the draught. When this

operation has been performed correctly, the next part of the weaver’s

business is to connect the different leaves with the levers or treddles

by which they are to be moved, so that one or more may be raised or sunk

by every treddle successively, as may be required to produce the

peculiar pattern. These connections being made by coupling the different

parts of the apparatus by cords, this operation is called the cording.

In order to direct the operator in this part of his business, especially

if previously unacquainted with the particular pattern upon which he is

employed, plans are drawn upon paper, specimens of which will be found

in _figs._ 1103, 1104., &c. These plans are horizontal sections of a

loom, the heddles being represented across the paper at _a_, and the

treddles under them, and crossing them at right angles, at _b_. In

_figs._ 1103. and 1104. they are represented as if they were distinct

pieces of wood, those across being the under shaft of each leaf of

heddles, and those at the left hand the treddles. See WEAVING. In actual

weaving, the treddles are placed at right angles to the heddles, the

sinking cords descending perpendicularly as nearly as possible to the

centre of the latter. Placing them at the left hand, therefore, is only

for ready inspection, and for practical convenience. At _c_ a few

threads of warp are shown as they pass through the heddles, and the

thick lines denote the leaf with which each thread is connected. Thus,

in _fig._ 1103., the right-hand thread, next to _a_, passes through the

eye of a heddle upon the back leaf, and is disconnected with all the

other leaves; the next thread passes through a heddle on the second

leaf; the third, through the third leaf; the fourth, through the fourth

leaf; and the fifth, through the fifth or front leaf. One set of the

draught being now completed, the weaver recommences with the back leaf,

and proceeds in the same succession again to the front. Two sets of the

draught are represented in this figure, and the same succession, it is

understood by weavers (who seldom draw more than one set), must be

repeated until all the warp is included. When they proceed to apply the

cords, the right-hand part of the plan at _b_ serves as a guide. In all

the plans shown by these figures, excepting one which shall be noticed,

a connexion must be formed, by cording, between every leaf of heddles

and every treddle; for all the leaves must either rise or sink. The

raising motion is effected by coupling the leaf to one end of its

correspondent top lever; the other end of this lever is tied to the long

march below, and this to the treddle. The sinking connexion is carried

directly from under the leaf to the treddle. To direct a weaver which of

these connexions is to be formed with each treddle, a black spot is

placed when a leaf is to be raised, where the leaf and treddle intersect

each other upon the plan, and the sinking connexions are left blank. For

example, to cord, the treddle 1, to the back leaf, put a raising cord,

and to each of the other four, sinking cords; for the treddle 2, raise

the second leaf, and sink the remaining four, and so of the rest; the

spot always denoting the leaf or leaves to be raised. The _figs._ 1103.

and 1104. are drawn for the purpose of rendering the general principle

of this kind of plans familiar to those who have not been previously

acquainted with them; but those who have been accustomed to manufacture

and weave ornamented cloths, never consume time by representing either

heddles or treddles as solid or distinct bodies. They content themselves

with ruling a number of lines across a piece of paper, sufficient to

make the intervals between these lines represent the number of leaves

required. Upon these intervals, they merely mark the succession of the

draught, without producing every line to resemble a thread of warp. At

the left hand, they draw as many lines across the former as will afford

an interval for each treddle; and in the squares produced by the

intersections of these lines, they place the dots, spots, or ciphers

which denote the raising cords. It is also common to continue the cross

lines which denote the treddle a considerable length beyond the

intersections, and to mark by dots, placed diagonally in the intervals,

the order or succession in which the treddles are to be pressed down in

weaving. The former of these modes has been adopted in the remaining

_figs._ to 1112.; but to save room, the latter has been avoided, and the

succession marked by the order of the figures under the intervals which

denote the treddles.

Some explanation of the various kinds of fanciful cloths represented by

these plans, may serve further to illustrate this subject, which is,

perhaps, the most important of any connected with the manufacture of

cloth, and will also enable a person who thoroughly studies them,

readily to acquire a competent knowledge of the other varieties in

weaving, which are boundless. _Figs._ 1103. and 1104. represent the

draught and cording of the two varieties of tweeled cloth wrought with

five leaves of heddles. The first is the regular or run tweel, which, as

every leaf rises in regular succession, while the rest are sunk,

interweaves the warp and woof only at every fifth interval, and as the

succession is uniform, the cloth when woven, presents the appearance of

parallel diagonal lines, at an angle of about 45° over the whole

surface. A tweel may have the regularity of its diagonal lines broken by

applying the cording as in _fig._ 1104. It will be observed, that in

both figures the draught of the warp is precisely the same, and that the

whole difference of the two plans consists in the order of placing the

spots denoting the raising cords, the first being regular and

successive, and the second alternate.

[Illustration: 1105 1106 1107 1108]

_Figs._ 1105. and 1106. are the regular and broken tweels which may be

produced with eight leaves. This properly is the tweel denominated satin

in the silk manufacture, although many webs of silk wrought with only

five leaves receive that appellation. Some of the finest Florentine

silks are tweeled with sixteen leaves. When the broken tweel of eight

leaves is used, the effect is much superior to what could be produced by

a smaller number; for in this, two leaves are passed in every interval,

which gives a much nearer resemblance to plain cloth than the others.

For this reason it is preferred in weaving the finest damasks. The

draught of the eight-leaf tweel differs in nothing from the others,

excepting in the number of leaves. The difference of the cording in the

broken tweel, will appear by inspecting the cyphers which mark the

raising cords, and comparing them with those of the broken tweel of five

leaves. _Fig._ 1107. represents the draught and cording of striped

dimity of a tweel of five leaves. This is the most simple species of

fanciful tweeling. It consists of ten leaves, or double the number of

the common tweel. These ten leaves are moved by only five treddles, in

the same manner as a common tweel. The stripe is formed by one set, of

the leaves flushing the warp, and the other set, the woof. The figure

represents a stripe formed by ten threads, alternately drawn through

each of the two sets of leaves. In this case, the stripe and the

intervals will be equally broad, and what is the stripe upon one side of

the cloth, will be the interval upon the other, and _vice versâ_. But

great variety of patterns may be introduced by drawing the warp in

greater or smaller portions through either set. The tweel is of the

regular kind, but may be broken by placing the cording as in _fig._

1104. It will be observed that the cording-marks of the lower or front

leaves are exactly the converse of the other set; for where a raising

mark is placed upon one, it is marked for sinking in the other; that is

to say, the mark is omitted; and all leaves which sink in the one, are

marked for raising in the other: thus, one thread rises in succession in

the back set, and four sink; but in the front set, four rise, and only

one sinks. The woof, of course, passing over the four sunk threads, and

under the raised one, in the first instance, is flushed above; but where

the reverse takes place, as in the second, it is flushed below; and thus

the appearance of a stripe is formed. The analogy subsisting between

striped dimity and dornock, is so great, that before noticing the plan

for fancy dimity, it may be proper to allude to the dornock, the plan of

which is represented by _fig._ 1108.

The draught of dornock is precisely the same in every respect with that

of striped dimity. It also consists of two sets of tweeling-heddles,

whether three, four, or five leaves are used for each set. The

right-hand set of treddles is also corded exactly in the same way, as

will appear by comparing them. But as the dimity is a continued stripe

from the beginning to the end of the web, only five treddles are

required to move ten leaves. The dornock being checker-work, the weaver

must possess the power of reversing this at pleasure. He therefore adds

five more treddles, the cording of which is exactly the reverse of the

former; that is to say, the back leaves, in the former case, having one

leaf raised, and four sunk, have, by working with these additional

treddles, one leaf sunk and four leaves raised. The front leaves are in

the same manner reversed, and the mounting is complete. So long as the

weaver continues to work with either set, a stripe will be formed, as in

the dimity; but when he changes his feet from one set to the other, the

whole effect is reversed, and the checkers formed. The dornock pattern

upon the design-paper, _fig._ 1108., may be thus explained: let every

square of the design represent five threads upon either set of the

heddles, which are said by weavers to be once over the draught,

supposing the tweel to be one of five leaves; draw three parallel lines,

as under, to form two intervals, each representing one of the sets; the

draught will then be as follows:--

+-------------------------------+

| 4 1 4 1 1 4 1 |

+-------------------------------+

| 4 4 1 1 1 4 4 |

+-------------------------------+

The above is exactly so much of the pattern as is there laid down, to

show its appearance; but one whole range of the pattern is completed by

the figure 1, nearest to the right hand upon the lower interval between

the lines, and the remaining figures, nearer to the right, form the

beginning of a second range or set. These are to be repeated in the same

way across the whole warp. The lower interval represents the five front

leaves; the upper interval, the five back ones. The first figure 4,

denotes that five threads are to be successively drawn upon the back

leaves, and this operation repeated four times. The first figure 4, in

the lower interval, expresses that the same is to be done upon the front

leaves; and each figure, by its diagonal position, shows how often, and

in what succession, five threads are to be drawn upon the leaves which

the interval in which it is placed represents.

Dornocks of more extensive patterns are sometimes woven with 3, 4, 5,

and even 6 sets of leaves; but after the leaves exceed 15 in number,

they both occupy an inconvenient space, and are very unwieldy to work.

For these reasons the diaper harness is in almost every instance

preferred.

[Illustration: 1109]

_Fig._ 1109. represents the draught and cording of a fanciful species of

dimity, in which it will be observed that the warp is not drawn directly

from the back to the front leaf, as in the former examples; but when it

has arrived at either external leaf, the draught is reversed, and

returns gradually to the other. The same draught is frequently used in

tweeling, when it is wished that the diagonal lines should appear upon

the cloth in a zigzag direction. This plan exhibits the draught and

cording which will produce the pattern upon the design-paper in _fig._

1103. _a_. Were all the squares produced by the intersection of the

lines denoting the leaves and treddles, where the raised dots are

placed, filled the same as on the design, they would produce the effect

of exactly one-fourth of that pattern. This is caused by the reversing

of the draught, which gives the other side reversed as on the design;

and when all the treddles, from 1 to 16, have been successively used in

the working, one-half of the pattern will become complete. The weaver

then goes again over his treddles, in the reversed order of the numbers,

from 17 to 30, when the other half of the pattern will be completed.

From this similarity of the cording to the design, it is easy, when a

design is given, to make out the draught and cording proper to work it;

and when the cording is given, to see its effect upon the design.

[Illustration: 1110]

_Fig._ 1110. represents the draught of the diaper mounting, and the

cording of the front leaves, which are moved by treddles. From the plan,

it will appear that 5 threads are included in every mail of the harness,

and that these are drawn in single threads through the front leaves. The

cording forms an exception to the general rules, that when one or more

leaves are raised, all the rest must be sunk; for in this instance, one

leaf rises, one sinks, and three remain stationary. An additional mark,

therefore, is used in this plan. The dots, as formerly, denote raising

cords; the blanks, sinking cords; and where the cord is to be totally

omitted, the cross marks × are placed.

[Illustration: 1111]

_Fig._ 1111. is the draught and cording of a spot whose two sides are

similar, but reversed. That upon the plan forms a diamond, similar to

the one drawn upon the design paper in the diagram, but smaller in size.

The draught here is reversed, as in the dimity plan, and the treading is

also to be reversed, after arriving at 6, to complete the diamond. Like

it, too, the raising marks form one-fourth of the pattern. In weaving

spots, they are commonly placed at intervals, with a portion of plain

cloth between them, and in alternate rows, the spots of one row being

between those of the other. But as intervals of plain cloth must take

place, both by the warp and woof, 2 leaves are added for that purpose.

The front, or ground leaf, includes every second thread of the whole

warp; the second, or plain leaf, that part which forms the intervals by

the warp. The remaining leaves form the spots; the first six being

allotted to one row of spots, and the second six to the next row; where

each spot is in the centre between the former. The reversed draught of

the first is shown entire, and is succeeded by 12 threads of plain.

One-half of the draught of the next row is then given, which is to be

completed exactly like the first, and succeeded by 12 threads more of

plain; when, one set of the pattern being finished, the same succession

is to be repeated over the whole warp. As spots are formed by inserting

woof of coarser dimensions than that which forms the fabric, every

second thread only is allotted for the spotting. Those included in the

front, or ground leaf, are represented by lines, and the spot threads

between them, by marks in the intervals, as in the other plans.

The treddles necessary to work this spot are, in number, 14. Of these,

the two in the centre, _a_, _b_, when pressed alternately, will produce

plain cloth; for _b_ raises the front leaf, which includes half of the

warp, and sinks all the rest; while _a_ exactly reverses the operation.

The spot-treddles on the right hand work the row contained in the first

six spot-leaves; and those upon the left hand, the row contained in the

second six. In working spots, one thread, or shot of spotting-woof, and

two of plain, are successively inserted, by means of two separate

shuttles.

[Illustration: 1112]

Dissimilar spots, are those whose sides are quite different from each

other. The draught only of these is represented by _fig._ 1112. The

cording depends entirely upon the figure.

[Illustration: 1113]

_Fig._ 1113. represents any solid body composed of parts _lashed_

together. If the darkened squares be supposed to be beams of wood,

connected by cordage, they will give a precise idea of textile fabric.

The beams cannot come into actual contact, because, if the _lashing_

cords were as fine even as human hairs, they must still require space.

The thickness is that of one beam and one cord; but if the cords touch

each other, it may then be one beam and two cords; but it is not

possible in practical weaving to bring every thread of weft into actual

contact. It may therefore be assumed, that the thickness is equal to the

diameter of one thread of the warp, added to that of one yarn of the

weft; and when these are equal, the thickness of the cloth is double of

that diameter. Denser cloth would not be sufficiently pliant or

flexible.

[Illustration: 1114]

_Fig._ 1114. is a representation of a section of cloth of an open

fabric, where the round dots which represent the warp are placed at a

considerable distance from each other.

[Illustration: 1115]

_Fig._ 1115. may be supposed a plain fabric of that description which

approaches the most nearly to any idea we can form of the most dense or

close contact of which yarn can be made susceptible. Here the warp is

supposed to be so tightly stretched in the loom as to retain entirely

the parallel state, without any curvature, and the whole flexure is

therefore given to the woof. This mode of weaving can never really

exist; but if the warp be sufficiently strong to bear any tight

stretching, and the woof be spun very soft and flexible, something very

near it may be produced. This way of making cloth is well fitted for

those goods which require to give considerable warmth; but they are

sometimes the means of very gross fraud and imposition; for if the warp

is made of very slender threads, and the woof of slackly twisted cotton

or woollen yarn, where the fibrils of the stuff, being but slightly

brought into contact, are rough and oozy, a great appearance of

thickness and strength may be given to the eye, when the cloth is

absolutely so flimsy, that it may be torn asunder as easily as a sheet

of writing-paper. Many frauds of this kind are practised.

[Illustration: 1116 1117]

In _fig._ 1116. is given a representation of the position of a fabric of

cloth in section, as it is in the loom before the warp has been closed

upon the woof, which still appears as a straight line. This figure may

usefully illustrate the direction and ratio of contraction which must

unavoidably take place in every kind of cloth, according to the density

of the texture, the dimensions of the threads, and the description of

the cloth. Let A, B, represent one thread of woof completely stretched

by the velocity of the shuttle in passing between the threads of warp

which are represented by the round dots 1, 2, &c., and those

distinguished by 8, 9, &c. When these threads are closed by the

operation of the heddles to form the inner texture, the first tendency

will be to move in the direction 1 _b_, 2 _b_, &c., for those above, and

in that of 8 _a_, 9 _a_, &c., for those below; but the contraction for

A, B, by its deviation from a straight to a curved line, in consequence

of the compression of the warp threads 1 _b_, 2 _b_, &c., and 1 _a_, 2

_a_, &c., in closing, will produce, by the action of the two powers at

right angles to each other, the oblique or diagonal direction denoted by

the lines 1, 8-2, 9, to the left, for the threads above, and that

expressed by the lines 2, 8-3, 9, &c., to the right, for the threads

below. Now, as the whole deviation is produced by the flexure of the

thread A, B, if A is supposed to be placed at the middle of the cloth,

equidistant from the two extremities, or _selvages_ as they are called

by weavers, the thread at 1 may be supposed to move really in the

direction 1 _b_, and all the others to approach to it in the directions

represented, whilst those to the right would approach in the same ratio,

but the line of approximation would be inverted. _Fig._ 1117. represents

that common fabric used for lawns, muslins, and the middle kind of

goods, the excellence of which neither consists in the greatest

strength, nor in the greatest transparency. It is entirely a medium

between _fig._ 1114. and _fig._ 1115.

[Illustration: 1118]

In the efforts to give great strength and thickness to cloth, it will be

obvious that the common mode of weaving, by constant intersection of

warp and woof, although it may be perhaps the best which can be devised

for the former, presents invincible obstructions to the latter, beyond a

certain limit. To remedy this, two modes of weaving are in common use,

which, while they add to the power of compressing a great quantity of

materials in a small compass, possess the additional advantage of

affording much facility for adding ornament to the superficies of the

fabric. The first of these is double cloth, or two webs woven together,

and joined by the operation. This is chiefly used for carpets; and its

geometrical principles are entirely the same as those of plain cloth,

supposing the webs to be sewed together. A section of the cloth will be

found in _fig._ 1118. See CARPET.

[Illustration: 1119]

Of the simplest kind of tweeled fabrics, a section is given in _fig._

1119.

The great and prominent advantage of the tweeled fabric, in point of

texture, arises from the facility with which a very great quantity of

materials may be put closely together. In the figure, the warp is

represented by the dots in the same straight line as in the plain

fabrics; but if we consider the direction and ratio of contraction, upon

principles similar to those laid down in the explanation given of _fig._

1116., we shall readily discover the very different way in which the

tweeled fabric is affected.

When the dotted lines are drawn at _a_, _b_, _c_, _d_, their direction

of contraction, instead of being upon every second or alternate thread,

is only upon every fifth thread, and the natural tendency would

consequently be, to bring the whole into the form represented by the

lines and dotted circles at _a_, _b_, _c_, _d_. In point, then, of

thickness, from the upper to the under superficies, it is evident that

the whole fabric has increased in the ratio of nearly three to one. On

the other hand, it will appear, that four threads or cylinders being

thus put together in one solid mass, might be supposed only one thread,

or like the strands of a rope before it is twisted; but, to remedy this,

the thread being shifted every time, the whole forms a body in which

much aggregate matter is compressed; but where, being less firmly

united, the accession of strength acquired by the accumulation of

materials is partially counteracted by the want of equal firmness of

junction.

[Illustration: 1120]

The second quality of the tweeled fabric, _susceptibility of receiving

ornament_, arises from its capability of being inverted at pleasure, as

in _fig._ 1120. In this figure we have, as before, four threads, and one

alternately intersected; but here the four threads marked 1 and 2 are

under the woof, while those marked 3 and 4 are above.

[Illustration: 1121]

_Fig._ 1121. represents that kind of tweeled work which produces an

ornamental effect, and adds even to the strength of a fabric, in so far

as accumulation of matter can be considered in that light. The figure

represents a piece of velvet cut in section, and of that kind which,

being woven upon a tweeled ground, is known by the name of Genoa velvet.

1st. Because, by combining a great quantity of material in a small

compass, they afford great warmth. 2nd. From the great resistance which

they oppose to external friction, they are very durable. And, 3rd.

Because, from the very nature of the texture, they afford the finest

means of rich ornamental decoration.

The use of velvet cloths in cold weather is a sufficient proof of the

truth of the first. The manufacture of plush, corduroy, and other stuffs

for the dress of those exposed to the accidents of laborious employment,

evinces the second; and the ornamented velvets and Wilton carpeting, are

demonstrative of the third of these positions.

In the figure, the diagonal form which both the warp and woof of cloth

assume, is very apparent from the smallness of the scale. Besides what

this adds to the strength of the cloth, the flushed part, which appears

interwoven at the darkly shaded intervals 1, 2, &c., forms, when

finished, the whole covering or upper surface. The principle, in so far

as regards texture, is entirely the same as any other tweeled fabric.

[Illustration: 1122]

_Fig._ 1122., which represents corduroy, or king’s cord, is merely

striped velvet. The principle is the same, and the figure shows that the

one is a copy of the other. The remaining figures represent those kinds

of work which are of the most flimsy and open description of texture;

those in which neither strength, warmth, nor durability are much

required, and of which openness and transparency are the chief

recommendations.

[Illustration: 1123]

_Fig._ 1123. represents common gauze, or _linau_, a substance very much

used for various purposes. The essential difference between this

description of cloth and all others, consists in the warp being turned

or twisted like a rope during the operation of weaving, and hence it

bears a considerable analogy to _lace_. The twining of gauze is not

continued in the same direction, but is alternately from right to left,

and _vice versâ_, between every intersection of the woof. The fabric of

gauze is always open, flimsy, and transparent; but, from the turning of

the warp, it possesses an uncommon degree of strength and tenacity in

proportion to the quantity of material which it contains. This quality,

together with the transparency of the fabric, renders it peculiarly

adapted for ornamental purposes of various kinds, particularly for

flowering or figuring, either in the loom; or by the needle. In the warp

of gauze; there arises a much greater degree of contraction during the

weaving, than in any other species of cloth; and this is produced by the

turning. The twisting between every intersection of weft amounts

precisely to one complete revolution of both threads; hence this

difference exists between this and every other species of weaving,

namely, that the one thread of warp is always above the woof, and the

contiguous thread is always below.

[Illustration: 1124]

_Fig._ 1124. represents a section of another species of twisted cloth,

which is known by the name of catgut, and which differs from the gauze

only, by being subjected to a greater degree of twine in weaving; for in

place of one revolution between each intersection, a revolution and a

half is always given; and thus the warp is alternately above and below,

as in other kinds of weaving.

[Illustration: 1125]

_Fig._ 1125. is a superficial representation of the most simple kind of

ornamental network produced in the loom. It is called a whip-net by

weavers, who use the term whip for any substance interwoven in cloth for

ornamental purposes, when it is distinct from the ground of the fabric.

In this, the difference is merely in the crossing of the warp; for it is

very evident that the crossings at 1, 2, 3, 4, and 5, are of different

threads from those at 6, 7, 8, and 9.

[Illustration: 1126]

_Fig._ 1126. represents, superficially, what is called the mail-net, and

is merely a combination of common gauze and the whip-net in the same

fabric. The gauze here being in the same direction as the dotted line in

the former figure, the whole fabric is evidently a continued succession

of right-angled triangles, of which the woof forms the basis, the gauze

part the perpendiculars, and the whip part the hypothenuses. The

contraction here being very different, it is necessary that the gauze

and whip parts should be stretched upon separate beams.

[Illustration: 1127]

In order to design ornamental figures upon cloths, the lines which are

drawn from the top to the bottom of the paper may be supposed to

represent the warp; and those drawn across, the woof of the web; any

number of threads being supposed to be included between every two lines.

The paper thus forms a double scale, by which, in the first instance,

the size and form of the pattern may be determined with great precision;

and the whole subsequent operations of the weaver regulated, both in

mounting and working his loom. To enable the projector of a new pattern

to judge properly of its effects, when transferred from the paper to the

cloth, it will be essentially necessary that he should bear constantly

in his view the comparative scale of magnitude which the design will

bear in each, regulating his ideas always by square or superficial

measurement. Thus, in the large design, _fig._ 1127., representing a

bird perched upon the branch of a tree, it will be proper, in the first

place, to count the number of spaces from the point of the bill to the

extremity of the tail; and to render this the more easy, it is to be

observed that every tenth line is drawn considerably bolder than the

others. This number in the design is 135 spaces. Counting again, from

the stem of the branch to the upper part of the bird’s head, he will

find 76 spaces. Between these spaces, therefore, the whole superficial

measure of the pattern is contained. By the measure of the paper, this

may be easily tried with a pair of compasses, and will be found to be

nearly 6-5/10 inches in length, by 3-3/16 inches in breadth. Now, if

this is to be woven in a reed containing 800 intervals in 37 inches, and

if every interval contains five threads, supposed to be contained

between every two parallel lines, the length will be 6·24 inches, and

the breadth 3·52 inches nearly; so that the figure upon the cloth would

be very nearly of the same dimensions as that upon the paper; but if a

1200 reed were used, instead of an 800, the dimensions would be

proportionally contracted.

A correct idea being formed of the design, the weaver may proceed to

mount his loom according to the pattern; and this is done by two

persons, one of whom takes from the design the instructions necessary

for the other to follow in tying his cords.

[Illustration: 1128 1129]

_Fig._ 1128. is a representation of the most simple species of

table-linen, which is merely an imitation of checker-work of various

sizes; and is known in Scotland, where the manufacture is chiefly

practised, by the name of Dornock. When a pattern is formed upon tweeled

cloth, by reversing the flushing, the two sides of the fabric being

dissimilar, one may be supposed to be represented by the black marks,

and the other by the part of the figure which is left uncoloured. For

such a pattern as this, two sets of common tweel-heddles, moved in the

ordinary way, by a double succession of heddles, are sufficient. The

other part of _fig._ 1128. is a design of that intermediate kind of

ornamental work which is called diaper, and which partakes partly of the

nature of the dornock, and partly of that of the damask and tapestry.

The principle upon which all these descriptions of goods are woven is

entirely the same, and the only difference is in the extent of the

design, and the means by which it is executed. _Fig._ 1129. is a design

for a border of a handkerchief or napkin, which may be executed either

in the manner of damask, or as the spotting is practised in the lighter

fabrics.

THENARD’S BLUE, or COBALT BLUE, is prepared by digesting the oxide of

cobalt used in the potteries, with nitric acid, evaporating the nitrate

almost to dryness, diluting it with water, and filtering, to separate

some arseniate of iron, which usually precipitates. The clear liquor is

to be poured into a solution of phosphate of soda, whence an insoluble

phosphate of cobalt falls. This being well washed, is to be intimately

mixed in its soft state with eight times its weight of well-washed

gelatinous alumina, which has been obtained by pouring a solution of

alum into water of ammonia in excess. The uniformly coloured paste is to

be spread upon plates, dried in a stove, then bruised dry in a mortar,

enclosed in a crucible, and subjected to a cherry-red heat for half an

hour. On taking out the crucible, and letting it cool, the fine blue

pigment is to be removed into a bottle, which is to be stoppered till

used.

The arseniate of cobalt may be substituted, in the above process, for

the phosphate, but it must be mixed with sixteen times its weight of the

washed gelatinous alumina. The arseniate is procured by pouring the

dilute nitrate of cobalt into a solution of arseniate of potassa. If

nitrate of cobalt be mixed with the alumina, and the mixture be treated

as above described, a blue pigment will also be obtained, but paler than

the preceding, showing that the colour consists essentially of alumina

stained with oxide of cobalt.

THERMOMETER, signifies the measure of heat. Its description belongs to a

treatise on chemical physics.

THERMOSTAT, is the name of an apparatus for regulating temperature, in

vaporization, distillation, heating baths or hothouses, arid ventilating

apartments, &c.; for which I obtained a patent in the year 1831. It

operates upon the physical principle, that when two thin metallic bars

of different expansibilities are riveted or soldered facewise together,

any change of temperature in them will cause a sensible movement of

flexure in the compound bar, to one side or other; which movement may be

made to operate, by the intervention of levers, &c., in any desired

degree, upon valves, stopcocks, stove-registers, air-ventilators, &c.;

so as to regulate the temperature of the media in which the said

compound bars are placed. Two long rulers, one of steel, and one of hard

hammered brass, riveted together, answer very well; the object being not

simply to _indicate_, but to _control_ or _modify_ temperature. The

following diagrams will illustrate a few out of the numerous

applications of this instrument:--

[Illustration: 1130]

_Fig._ 1130. _a_, _b_, is a single thermostatic bar, consisting of two

or more bars or rulers of differently expansible solids (of which, in

certain cases, wood may be one): these bars or rulers are firmly riveted

or soldered together, face to face. One end of the compound bar is fixed

by bolts at _a_, to the interior of the containing cistern, boiler, or

apartment, _a_, _l_, _m_, _b_, whereof the temperature has to be

regulated, and the other end of the compound bar at _b_, is left free to

move down towards _c_, by the flexure which will take place when its

temperature is raised.

The end _b_, is connected by a link, _b_, _d_, with a lever _d_, _e_,

which is moved by the flexure into the dotted position _b_, _g_, causing

the turning-valve, air-ventilator, or register, _o_, _n_, to revolve

with a corresponding angular motion, whereby the lever will raise the

equipoised slide-damper _k_, _i_, which is suspended by a link from the

end _e_, of the lever _e_, _d_, into the position _k_, _h_. Thus a

hothouse or a water-bath may have its temperature regulated by the

contemporaneous admission of warm, and discharge of cold air, or water.

[Illustration: 1131]

_Fig._ 1131. _a_, _b_, _c_, is a thermostatic hoop, immersed

horizontally beneath the surface of the water-bath of a still. The hoop

is fixed at _a_, and the two ends _b_, _c_, are connected by two links

_b d_, _c d_, with a straight sliding rod _d_, _h_, to which the hoop

will give an endwise motion, when its temperature is altered; _e_; is an

adjusting screw-nut on the rod _d_, _h_, for setting the lever _f_, _g_,

which is fixed on the axis of the turning-valve or cock _f_; at any

desired position, so that the valve may be opened or shut at any desired

temperature, corresponding to the widening of the points _b_, _c_, and

the consentaneous retraction of the point _d_, towards the circumference

_a_, _b_, _c_, of the hoop. _g_, _h_, is an arc graduated by a

thermometer, after the screw-piece _e_ has been adjusted. Through a hole

at _h_, the guide-rod passes. _i_, is the cold-water cistern; _i_, _f_,

_k_, the pipe to admit cold water; _l_, the overflow pipe, at which the

excess of hot water runs off.

[Illustration: 1132]

_Fig._ 1132. shows a pair of thermostatic bars, bolted fast together at

the ends _a_. The free ends _b_, _c_, are of unequal length, so as to

act by the cross links _d_, _f_, on the stopcock _e_. The links are

jointed to the handle of the turning plug of the cock, on opposite

sides of its centre; whereby that plug will be turned round in

proportion to the widening of the points _b_, _c_. _h_, _g_, is the pipe

communicating with the stopcock.

[Illustration: 1133]

Suppose that for certain purposes in pharmacy, dyeing, or any other

chemical art, a water-bath is required to be maintained steadily at a

temperature of 150° F.: let the combined thermostatic bars, hinged

together at _e_, _f_, _fig._ 1133., be placed in the bath, between the

outer and inner vessels _a_, _b_, _c_, _d_, being bolted fast to the

inner vessel at _g_; and have their sliding rod _k_, connected by a link

with a lever fixed upon the turning plug of the stopcock _i_, which

introduces cold water from a cistern _m_, through a pipe _m_, _i_, _n_,

into the bottom part of the bath. The length of the link must be so

adjusted that the flexure of the bars, when they are at a temperature of

150°, will open the said stopcock, and admit cold water to pass into the

bottom of the bath through the pipe _i_, _n_, whereby hot water will be

displaced at the top of the bath through an open overflow-pipe at _q_.

An oil bath may be regulated on the same plan; the hot oil overflowing

from _q_, into a refrigeratory worm, from which it may be restored to

the cistern _m_. When a water bath is heated by the distribution of a

tortuous steam pipe through it, as _i_, _n_, _o_, _p_, it will be

necessary to connect the link of the thermostatic bars with the lever of

the turning plug of the steam-cock, or of the throttle valve _i_, in

order that the bars, by their flexure, may shut or open the steam

passage more or less, according as the temperature of the water in the

bath shall tend more or less to deviate from the pitch to which the

apparatus has been adjusted. The water of the condensed steam will pass

off from the sloping winding-pipe _i_, _n_, _o_, _p_, through the

sloping orifice _p_. A saline, acid, or alkaline bath has a boiling

temperature proportional to its degree of concentration, and may

therefore have its heat regulated by immersing a thermostat in it, and

connecting the working part of the instrument with a stopcock _i_, which

will admit water to dilute the bath whenever by evaporation it has

become concentrated, and has acquired a higher boiling point. The space

for the bath, between the outer and inner pans, should communicate by

one pipe with the water-cistern _m_; and by another pipe, with a safety

cistern _r_, into which the bath may be allowed to overflow during any

sudden excess of ebullition.

[Illustration: 1136]

_Fig._ 1136. is a thermostatic apparatus, composed of three pairs of

bars _d_, _d_, _d_, which are represented in a state of flexure by heat;

but they become nearly straight and parallel when cold, _a_, _b_, _c_,

is a guide rod, fixed at one end by an adjusting screw _e_, in the

strong frame _f_, _e_, having deep guide grooves at the sides. _f_, _g_,

is the working-rod, which moves endways when the bars _d_, _d_, _d_,

operate by heat or cold. A square register-plate _h_, _g_, may be

affixed to the rod _f_, _g_, so as to be moved backwards and forwards

thereby, according to the variations of temperature; or the rod _f_,

_g_, may cause the circular turning air-register _i_, to revolve by rack

and wheel-work, or by a chain and pulley. The register-plate _h_, _g_,

or turning register _i_, is situated at the ceiling or upper part of the

chamber, and serves to let out hot air. _k_, is a pulley, over which a

cord runs to raise or lower a hot-air register _l_, which may be

situated near the floor of the apartment or hothouse, to admit hot air

into the room. _c_, is a milled head, for adjusting the thermostat, by

means of the screw at _e_, in order that it may regulate the temperature

to any degree.

[Illustration: 1137]

_Fig._ 1137. represents a chimney, furnished with a _pyrostat_ _a_, _b_,

_c_, acting by the links _b_, _d_, _e_, _c_, on a damper _f_, _h_, _g_.

The more expansible metal is in the present example supposed to be on

the outside. The plane of the damper-plate will, in this case, be turned

more directly into the passage of the draught through the chimney by

increase of temperature.

[Illustration: 1135]

_Fig._ 1135. represents a circular turning register, such as is used for

a stove, or stove-grate, or for ventilating apartments; it is furnished

with a series of spiral thermostatic bars, each bar being fixed fast at

the circumference of the circle _b_, _c_, of the fixed plate of the

air-register; and all the bars act in concert at the centre _a_, of the

twining part of the register, by their ends being inserted between the

teeth of a small pinion, or by being jointed to the central part of the

turning plate by small pins.

[Illustration: 1134]

_Fig._ 1134. represents another arrangement of my thermostatic apparatus

applied to a circular turning register, like the preceding, for

ventilating apartments. Two pairs of compound bars are applied so as to

act in concert, by means of the links _a c_, _b c_, on the opposite ends

of a short lever, which is fixed on the central part of the turning

plate of the air-register. The two pairs of compound bars _a_, _b_, are

fastened to the circumference of the fixed plate of the turning

adjusting screws. Their motion or flexure is transmitted by the links _a

c_, and _b c_, to the turning plate, about its centre, for the purpose

of shutting or opening the ventilating sectorial apertures, more or

less, according to the temperature of the air which surrounds the

thermostatic turning register. By adjusting the screws _a d_, and _b c_,

the turning register is made to close all its apertures at any desired

degree of temperature; but whenever the air is above that temperature,

the flexure of the compound bars will open the apertures.

THIMBLE (_Dé à coudre_, Fr.; _Fingerhut_ (_fingerhat_), Germ.); is a

small truncated metallic cone, deviating little from a cylinder, smooth

within, and symmetrically pitted on the outside with numerous rows of

indentations, which is put upon the tip of the middle finger of the

right hand, to enable it to push the needle readily and safely through

cloth or leather, in the act of sewing. This little instrument is

fashioned in two ways; either with a pitted round end, or without one;

the latter, called the open thimble, being employed by tailors,

upholsterers, and, generally speaking, by _needle-men_. The following

ingenious process for making this essential implement, the contrivance

of M. M. Rouy and Berthier, of Paris, has been much celebrated, and very

successful. Sheet-iron, one twenty-fourth of an inch thick, is cut into

strips, of dimensions suited to the intended size of the thimbles. These

strips are passed under a punch-press, whereby they are cut into discs

of about 2 inches diameter, tagged together by a tail. Each strip

contains one dozen of these blanks. A child is employed to make them

red-hot, and to lay them on a mandril nicely fitted to their size. The

workman now strikes the middle of each with a round-faced punch, about

the thickness of his finger, and thus sinks it into the concavity of the

first mandril. He then transfers it successively to another mandril,

which has five hollows of successively increasing depth; and, by

striking it into them, brings it to the proper shape.

A second workman takes this rude thimble, sticks it in the chuck of his

lathe, in order to polish it within, then turns it outside, marks the

circles for the gold ornament, and indents the pits most cleverly with a

kind of milling tool. The thimbles are next annealed, brightened, and

gilt inside, with a very thin cone of gold leaf, which is firmly united

to the surface of the iron, simply by the strong pressure of a smooth

steel mandril. A gold fillet is applied to the outside, in an annular

space turned to receive it, being fixed, by pressure at the edges, into

a minute groove formed on the lathe.

Thimbles are made in this country by means of moulds in the

stamping-machine. See STAMPING OF METALS.

THORINA, is a primitive earth, with a metallic basis, discovered in

1828, by Berzelius. It was extracted from the mineral _thorite_, of

which it constitutes 58 per cent., and where it is associated with the

oxides of iron, lead, manganese, tin, and uranium, besides earths and

alkalis, in all 12 substances. Pure thorina is a white powder, without

taste, smell, or alkaline reaction on litmus. When dried and calcined,

it is not affected by either the nitric or muriatic acid. It may be

fused with borax into a transparent glass, but not with potash or soda.

Fresh precipitated thorina is a hydrate, which dissolves readily in the

above acids, as well as in solutions of the carbonates of potash, soda,

and ammonia, but not in these alkalis in a pure state. This earth

consists of 74·5 parts of the metal _thorinum_, combined with 100 of

oxygen. Its hydrate contains one equivalent prime of water. It is

hitherto merely a chemical curiosity, remarkable chiefly for a density

of 9·402, far greater than that of all the earths, and even of copper.

[Illustration: 1138]

THREAD MANUFACTURE. The doubling and twisting of cotton or linen yarn

into a compact thread, for weaving bobbin-net, or for sewing garments,

is performed by a machine resembling the throstle of the cotton-spinner.

_Fig._ 1138. shows the thread-frame in a transverse section,

perpendicular to its length. _a_, is the strong framing of cast iron;

_b_, is the _creel_, or shelf, in which the bobbins of yarn _l_, _l_,

are set loosely upon their respective skewers, along the whole line of

the machine, their lower ends turning in oiled steps, and their upper in

wire eyes; _c_, is a glass rod, across which the yarn runs as it is

unwound; _d_, _d_, are oblong narrow troughs, lined with lead, and

filled with water, for moistening the thread during its torsion; the

threads being made to pass through eyes at the bottom of the fork _e_,

which has an upright stem for lifting it out, without wetting the

fingers, when any thing goes amiss; _f_, _f_, are the pressing rollers,

the under one _g_, being of smooth iron, and the upper one _h_, of

box-wood; the former extends from end to end of the frame, in lengths

comprehending 18 threads, which are joined by square pieces, as in the

drawing-rollers of the mule-jenny. The necks of the under rollers are

supported, at the ends and the middle, by the standards _i_, secured to

square bases _j_, both made of cast iron. The upper cylinder has an iron

axis, and is formed of as many rollers as there are threads; each roller

being kept in its place upon the lower one by the guides _k_, whose

vertical slots receive the ends of the axes.

The yarn delivered by the bobbin _l_, glides over the rod _c_, and

descends into the trough _d_, _e_, where it gets wetted; on emerging, it

goes along the bottom of the roller _g_, turns up, so as to pass between

it and _h_, then turns round the top of _h_, and finally proceeds

obliquely downwards, to be wound upon the bobbin _m_, after traversing

the guide-eye _n_. These guides are fixed to the end of a plate, which

may be turned up by a hinge-joint at _o_, to make room for the bobbins

to be changed.

There are three distinct simultaneous movements to be considered in this

machine: 1. that of the rollers, or rather of the under roller, for the

upper one revolves merely by friction; 2. that of the spindles _m_,

_s´_; 3. the up-and-down motion of the bobbins upon the spindles.

The first of these motions is produced by means of toothed wheels, upon

the right hand of the under set of rollers. The second motion, that of

the spindles, is effected by the drum _z_, which extends the whole

length of the frame, turning upon the shaft _v_, and communicating its

rotatory movement (derived from the steam pulley) to the whorl _b´_, of

the spindles, by means of the endless band or cord _a´_. Each of these

cords turns four spindles, two upon each side of the frame. They are

kept in a proper state of tension by the weights _c´_, which act

tangentially upon the circular arc _d´_, fixed to the extremity of the

bell-crank lever _e´ f´ g´_, and draw in a horizontal direction the

tension pulleys _h_, embraced by the cords. The third movement, or the

vertical traverse of the bobbins, along the spindles _m_, takes place as

follows:--

The end of one of the under rollers carries a pinion, which takes into a

carrier wheel, that communicates motion to a pinion upon the extremity

of the shaft _m´_, of the heart-shaped pulley _n´_. As this eccentric

revolves, it gives a reciprocating motion to the levers _o´_, _o´_,

which oscillate in a vertical plane round the points, _p´_, _p´_. The

extremities of these levers, on either side, act by means of the links

_q´_, upon the arms of the sliding sockets _r´_, and cause the vertical

rod _s´_, to slide up and down in guide-holes at _t´_, _u´_, along with

the cast-iron step _v´_, which bears the bottom washer of the bobbins.

The periphery of the heart-wheel _n´_, is seen to bear upon friction

wheels _x_, _x´_, set in frames adjusted by screws upon the lower end of

the bent levers, at such a distance from the point _p´_, as that the

traverse of the bobbins may be equal to the length of their barrel.

By adapting change pinions and their corresponding wheels to the

rollers, the delivery of the yarn may be increased or diminished in any

degree, so as to vary the degree of twist put into it by the uniform

rotation of the drum and spindles. The heart motion being derived from

that of the rollers, will necessarily vary with it.

Silk thread is commonly twisted in lengths of from 50 to 100 feet, with

hand reels, somewhat similar to those employed for making ropes by hand.

TILES. See BRICKS.

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 hardness it is intermediate between gold

and lead; it is very malleable, and may be laminated into foil less than

the thousandth of an inch in thickness; 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

redness with free access 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 disseminated in the antient rocks, particularly

granite; also in beds and veins, in large irregular masses, called

_stockwerks_; and in pebbles, an assemblage 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 access 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 Gallicia 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 Massachusetts.

The Cornish ores occur--1. in small strata or veins, or in masses; 2. in

stockwerks, or congeries of small veins; 3. in large veins; 4.

disseminated in alluvial deposits.

The stanniferous small veins, or thin flat masses, 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 Bottalack, 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 thickness

of these little veins rarely exceeds 6 inches, including the adhering

solidified granite, and is occasionally much less. 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 masses 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 thickness 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 Devonshire; 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 Tavistock in Devonshire.

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 associated, the one which dips to the north,

cuts across and throws out the one which dips to the south. See MINES,

p. 835.

[Illustration: 1139]

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 thickness 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 disseminated

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.

[Illustration: 1140]

The tin mine of Altenberg, in Saxony (_fig._ 1140., which is a vertical

projection in a plane passing from west to east,) is remarkable for a

stockwerke, or interlaced mass of ramifying veins, which has been worked

ever since the year 1458. The including rock is a primitive porphyry,

superposed upon gneiss; becoming very quartzose as it approaches the

lode. This is usually disseminated 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 dædalus, 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 abyss, 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 masses 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 accessory 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-pressure 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 gneiss. 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, &c.; 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 possible, 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.

[Illustration: 1141]

_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 successive 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 mass 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 successive beds, whose

thickness 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_.

_Mine tin_ requires peculiar care in its mechanical preparation or

dressing, on account of the presence of foreign metals, from which, as

we have stated, the stream tin is free.

1. As the mine tin is for the most part extremely dispersed through the

gangue, it must be all stamped and reduced to a very fine powder, to

allow the metallic particles to be separated from the stony matters.

2. As the density of tin-stone is much greater than that of most other

metallic ores, it is less apt to run off in the washing; and may,

therefore, be dressed so as to be completely stripped of every matter

not chemically combined.

3. As the peroxide of tin is not affected by a moderate heat, it may be

exposed to calcination; whereby the specific gravity of the associated

sulphurets and arseniurets is so diminished as to facilitate their

separation.

We may therefore conclude, that tin ore should be first of all pounded

very fine in the stamp-mill, then subjected to reiterated washings, and

afterwards calcined. The order of proceeding in Cornwall is as

follows:--

1. _Cleaning the ore._--This is usually done at the mouth of the gallery

of efflux, by agitating the ore in the stream of water as it runs out.

Sometimes the ore is laid on a grating, under a fall of water.

2. _Sorting._--The ore thus cleaned, is sorted on the grate, into four

heaps: 1. stones rich in tin; 2. stones containing both tin and copper

ore; 3. copper ore; 4. sterile pieces, composed in a great measure of

stony gangue, with iron and arsenical pyrites. In those veins where

there is no copper ore, the second and third heaps are obviously absent.

When present, the compound ore is broken into smaller pieces with a

mallet, and the fragments are sorted anew.

3. _Stamping._--The stanniferous fragments (No. 1.) are stamped into a

sand, of greater or less fineness, according to the dissemination of the

tin-stone in the gangue. The determination of the size of the sand, is

an object of great importance. It is regulated by a copper plate pierced

with small holes, through which every thing from the stamping-mill must

run off with the rapid stream introduced for this purpose. This plate

forms the front of the stamp cistern.

Several years ago, all the stamp mills were driven by water-wheels,

which limited the quantity of ore that could be worked to the hydraulic

power of the stream or waterfall; but since the steam engine has been

applied to this purpose, the annual product of tin has been greatly

increased. On the mine of Huel Vor, there are three steam engines

appropriated to the stamping-mills. Their force is 25 horses at least.

One of these machines, called _south stamps_, drives 48 pestles; a

second, called _old stamps_, drives 36; and a third, 24. The weight of

these pestles varies from 370 to 387 pounds; and they generally rise

through a space of 10-1/2 inches. The machine called _south stamps_, the

strongest of the three, gives 17-1/2 blows in the minute, each pestle

being lifted twice for every stroke of the piston. The steam engine of

this mill has a power of 25 horses, and it consumes 1062 bushels of

coals in the month. Three pestles constitute a battery, or stamp-box.

[Illustration: 1142]

_Washing and stamping of tin ores at Polgooth, near St. Austle._--The

stamps or pestles are of wood, 6 inches by 5-1/2 in the square: they

carry lifting bars _b_, secured with a wooden wedge and a bolt of iron,

and they terminate below in a lump of cast iron A, called the head,

which is fastened to them by a tail, and weighs about 2-1/2 cwts. The

shank of the pestle is strengthened with iron hoops. A turning-shaft

communicates motion to the stamps by cams stuck round its circumference,

so arranged that the second falls while the first and third of each set

are uplifted. There are 4 cams on one periphery, and the shaft makes 7

turns in the minute. Each stamp, therefore, gives 28 strokes per minute,

and falls through a space of 7-1/2 inches. The stamp chest is open

behind, so that the ore slips away under the pestles, by its weight,

along the inclined plane with the stream of water. The bottom of the

troughs consists of stamped ores. With 6 batteries of 6 pestles each, at

Poldice, near Redruth, 120 bags of ore are stamped in 12 hours; each bag

containing 18 gallons of 282 cubic inches; measuring altogether 352

cubic feet, and 864 cubic inches.

[Illustration: 1143 1144 1145 1146]

The openings in the front sides of the troughs are nearly 8 inches by

7-1/2: they are fitted with an iron frame, which is closed with sheet

iron, pierced with about 160 holes in the square inch, bored conically,

being narrower within. The ore, on issuing, deposits its _rough_ in the

first basin, and its slimes in the following basins. The rough is washed

in _buddles_ (see LEAD, page 751), and in _tossing tubs_; the slimes in

_trunks_, and upon a kind of twin tables, called _racks_. Into the

_tossing-tub_, or _dolly_, _fig._ 1143., the stamped ore is thrown,

along with a certain quantity of water, and a workman stirs it about

with an iron shovel for three or four minutes. He then removes a little

of the water with a handled pitcher, and strikes the sides of the tub

for 8 or 10 minutes with a hammer, which hastens the subsidence of the

denser parts. The water is next poured off by inclining the tub to one

side. In one operation of this kind, four distinct strata of the ores

may be procured, as indicated by the lines _a b_, _c d_, _e f g_, _h i

k_, in the figure. The portion A is to be washed again in the

_trunking-box_, _figs._ 1144, 1145.; B is to be washed upon the German

chests or racks, _fig._ 1146.; C, the most considerable, is put aside,

as schlich fit for the market; D, forming a nucleus the centre of the

tub, is to be passed through sieves of copper wire, having 18 meshes in

the square inch. This product thus affords a portion D´, which passes

through the sieve, and D´´ which remains upon it; the latter is

sometimes thrown away, and at others is subjected to the operation

called the _tie_, viz., a washing upon the sloping bottom of a long

trough.

The slimes are freed from the lighter mud in the trunking-box, _figs._

1144, 1145.; which is from 7 to 8 feet long. Being accumulated at M, the

workman pushes them back with a shovel from _a_ towards _b_. The

metallic portion is carried off, and deposited by the stream of water

upon the table; but the earthy matters are floated along into a basin

beyond it. The product collected in the chest is divided into two

portions; the one of which is washed once, and the other twice, upon the

_rack_, _fig._ 1146. This is composed of a frame C, which carries a

sloping board or table, susceptible of turning round to the right or

left upon two pivots, K, K. The head of the table is the inclined plane

T. A small board P, which is attached by a band of leather L, forms the

communication with the lower table C, whose slope is generally 5 inches

in its whole length of 9 feet; but this may vary with the nature of the

ore, being somewhat less when it is finely pulverized. The ore is thrown

upon T, in small portions of 20 or 25 lbs. A woman spreads it with a

rake, while a stream of water sweeps a part of it upon the table, where

it gets washed. The fine mud falls through a cross slit near the lower

end, into a basin B. After working for a few minutes, should the schlich

seem tolerably rich, the operative turns the table round its axis K, K,

so as to tumble it into the boxes below. The mud is in B; an impure

schlich in B´, which must be washed again upon the _rack_; and a schlich

fit for roasting in B´´.

The slope of the rack-table for washing the _roasted_ tin ore, is 7-3/4

inches in the 9 feet.

[Illustration: 1147]

_Crushing rolls at the Pembroke mines._--Waggons, moved on a railway by

an endless rope, bring the ore to be crushed, immediately over the

rolls, as shown in _fig._ 1147. A trap being opened in the side of the

waggon, the ore falls into the hopper T, whence it passes directly

between the twin cylinders C, C, and next upon the sieve D, which

receives a seesaw motion horizontally, by means of the rod L, and the

crank of the upright turning-shaft. The finer portion of ore, which

passes through that sieve, forms the heap S. The coarser portion is

tossed over the edge of the sieve, and falls between the cylinders C´

C´, upon a lower level, and forms the second heap S´ of sifted, and S´´

of unsifted, ore.

The holes of the sieves D, D´, being of the same size, the products S,

S´, are of the same fineness. S´´ is ground again, being mixed, in the

uppermost hopper T, along with the lumps from the waggons.

[Illustration: 1148]

The diameter and length of the under rolls (see _fig._ 1148.) are each

16 inches. _a b_, is the square end of the gudgeon _t_, which prevents

the shaft shifting laterally out of its place. The diameter of the upper

rolls is 18 inches, but their length is the same. Both are made of white

cast iron, _chilled_ or case-hardened by being cast in iron moulds

instead of sand; and they last a month, at least, when of good quality.

They make from 10 to 15 turns in a minute, according to the hardness of

the ores of tin or copper; and can grind about 50 tons of rich copper

ore in 12 hours; but less of the poorer sort.

The next process is the calcination in the _burning-house_; which

includes several reverberatory furnaces. At the mine of Poldice, they

are 4 or 5 yards long, by from 2-1/2 to 3 yards wide. Their hearth is

horizontal; the elevation, about 26 inches high near the fireplace,

sinks slightly towards the chimney. There is but one opening, which is

in the front; it is closed by a plate-iron door, turning on hinges.

Above the door there is a chimney, to let the sulphureous and arsenical

vapours fly off, which escape out of the hearth, without annoying the

workmen. This chimney leads to horizontal flues, in which the arsenious

acid is condensed.

Six hundred weight of ore are introduced; the calcination of which takes

from 12 to 18 hours, according to the quantity of pyrites contained in

the ore. At the beginning of the operation, a moderate heat is applied,

after which it is pushed to a dull red, and kept so during several

hours. The door is shut; the materials are stirred from time to time

with an iron rake, to expose new surfaces, and prevent them from

agglutinating or _kerning_, as the workmen say. The more pyrites is

present, the more turning is necessary. Should the ore contain black

oxide of iron, it becomes peroxidized, and is then easily removed by a

subsequent washing.

[Illustration: 1149 1150]

_Figs._ 1149, 1150. represent the furnace employed at Altenberg, in

Saxony, for roasting tin ores. _a_ is the grate; _b_, the sole of the

roasting hearth; _c_, an opening in the arched roof for introducing the

dried schlich (the ground and elutriated ore); _d_, is the smoke-mantle

or chimney-hood, at the end of the furnace, under which the workmen turn

over the spread schlich, with long iron rods bent at their ends; _e_, is

the poison vent, which conducts the arsenical vapours to the poison

chamber (_gifthaus_) of condensation.

When the ore is sufficiently calcined, as is shown by its ceasing to

exhale vapours, it is taken out, and exposed for some days to the action

of the air, which decomposes the sulphurets, or changes them into

sulphates. The ore is next put into a tub filled with water, stirred up

with a wooden rake, and left to settle; by which means the sulphate of

copper that may have been formed, is dissolved out. After some time,

this water is drawn off into a large tank, and its copper recovered by

precipitation with pieces of old iron. In this way, almost all the

copper contained in the tin ore is extracted.

The calcined ore is sifted, and treated again on the racks, as above

described. The pure schlich, called _black tin_, is sold under this name

to the smelters; and that which collects on the middle part of the

inclined wash-tables, being much mixed with wolfram, is called _mock

lead_. This is passed once more through the stamps, and washed; when it

also is sold as _black tin_.

Stream tin is dressed by similar methods: 1. by washing in a

trunking-box, of such dimensions that the workman stands upon it in

thick boots, and makes a skilful use of the rake; 2. by separating the

larger conglomerate pebbles from the smaller pure ones; picking,

stamping, and washing, on a kind of _sleeping-tables_. See METALLURGY,

_figs._ 677, 678.

The tin ores of Cornwall and Devonshire are all reduced within the

counties where they are mined, as the laws prohibit their exportation

out of them. Private interests suffer no injury from this prohibition;

because the vessels which bring the fuel from Wales, for smelting these

ores, return to Swansea and Neath loaded with copper ores.

The smelting-works belong in general to individuals who possess no tin

mines, but who purchase at the cheapest rate the ores from the mining

proprietors. The ores are appraised according to their contents in

metal, and its fineness; conditions which they determine by the

following mode of assay. When a certain number of bags of ore, of nearly

the same quality, are brought to the works, a small sample is taken from

each bag, and the whole are well blended. Two ounces of this average ore

are mixed with about 4 per cent. of ground coal, put into an open

earthen crucible, and heated in an air furnace (in area about 10 inches

square) till reduction takes place. As the furnace is very hot when the

crucible is introduced, the assay is finished in about a quarter of an

hour. The metal thus revived, is poured into a mould, and what remains

in the crucible is pounded in a mortar, that the grains of tin may be

added to the ingot.

This method, though imperfect in a chemical point of view, serves the

smelter’s purpose, as it affords him a similar result to what he would

get on the great scale. A more exact assay would be obtained by fusing,

in a crucible lined with hard-rammed charcoal, the ore mixed with 5 per

cent. of ground glass of borax. To the crucible a gentle heat should be

applied during the first hour, then a strong heat during the second

hour, and, lastly, an intense heat for a quarter of an hour. This

process brings out from 4 to 5 per cent. more tin than the other; but it

has the inconvenience of reducing the iron, should any be present; which

by subsequent solution in nitric acid will be readily shown. This assay

would be too tedious for the smelter, who may have occasion to try a

great many samples in one day.

A Dictionary of Arts, Manufactures and Mines containing a clear exposition of their principles and practice · 第 395 / 421 题