Chapter M: D’Arcet states the analysis of Marseilles soap at (8)

Having now detailed, with sufficient minuteness, the construction of the chamber, I shall next describe the mode of operating with it. There are at least two plans at present in use for burning the sulphur continuously in the oven. In the one, the sulphur is laid on the hearth _e_, (or rather on the flat hearth in the separate oven, above described,) and is kindled by a slight fire placed under it; which fire, however, is allowed to go out after the first day, because the oven becomes by that time sufficiently heated by the sulphur flames to carry on the subsequent combustion. Upon the hearth, an iron tripod is set, supporting, a few inches above it, a hemispherical cast-iron bowl (basin) charged with nitre and its decomposing proportion of strong sulphuric acid. In the other plan, 12 parts of bruised sulphur, and 1 of nitre, are mixed in a leaden trough on the floor with 1 of strong sulphuric acid, and the mixture is shovelled through the sliding iron door upon the hot hearth. The successive charges of sulphur are proportioned, of course, to the size of the chamber. In one of the largest, which is 120 feet long, 20 broad, and 16 high, 12 cwt. are burned in the course of 24 hours, divided into 6 charges, every fourth hour, of 2 cwt. each. In chambers of one-sixth greater capacity, containing 1400 metres cube, 1 ton of sulphur is burned in 24 hours. This immense production was first introduced at Chaunay and Dieuze, under the management of M. Clement-Desormes. The bottom of the chamber should be covered at first with a thin stratum of sulphuric acid, of spec. grav. 1·07, which decomposes nitrous acid into oxygen and nitrous gas; but not with mere water, which would absorb the nitrous acid vapours, and withdraw them from their aerial sphere of action. The vapour of nitric acid, disengaged from the nitre on the hearth of the oven, when brought into intimate contact with the sulphurous acid, either gives up oxygen to it, becomes itself nitrous gas, and converts it into sulphuric acid; or combines with the sulphurous acid into the crystalline compound above described, which, the moment it meets with moisture, is decomposed into sulphuric acid and nitrous gas. The atmospherical oxygen of the chamber immediately reconverts this gas into nitrous or nitric acid fumes, which are again ready, with the co-operation of sulphurous acid gas and aqueous vapour, to produce fresh quantities of hydrous sulphuric acid (oil of vitriol) and nitrous gas. At low temperatures, this curious play of chemical affinities has a great tendency to form the crystalline compound, and to deposit it in a crust of considerable thickness (from one-half to one inch) on the sides of the chamber, so as to render the process inoperative. A circumstance of this kind occurred, in a very striking manner, during winter, in a manufacture of oil of vitriol in Russia; and it has sometimes occurred, to a moderate extent, in Scotland. It is called, at Marseilles, the _maladie des chambres_. It may be certainly prevented, by maintaining the interior of the chamber, by a jet of steam, at a temperature of 100° F. When these crystals fall into the dilute acid at the bottom, they are decomposed with a violent effervescence, and a hissing gurgling noise, somewhat like that of a tun of beer in brisk fermentation.

M. Clement-Desormes demonstrated the proposition relative to the influence of temperature by a decisive experiment. He took a glass globe, furnished with three tubulures, and put a bit of ice into it. Through the first opening he then introduced sulphurous acid gas; through the second, oxygen; and through the third, nitrous gas (deutoxide of azote). While the globe was kept cool, by being plunged in iced water, no sulphuric acid was formed, though all the ingredients essential to its production were present. But on exposing the globe to a temperature of 100° Fahr., the four bodies began immediately to react on each other, and oil of vitriol was condensed in visible _striæ_.

The introduction of steam is a modern invention, which has vastly facilitated and increased the production of oil of vitriol. It serves, by powerful agitation, not only to mix the different gaseous molecules intimately together, but to impel them against each other, and thus bring them within the sphere of their mutual chemical attraction. This is its mechanical effect. Its chemical agency is still more important. By supplying moisture at every point of the immense included space, it determines the formation of hydrous sulphuric acid, from the compound of nitric, nitrous, sulphurous, and dry sulphuric acids. No sooner is this reaction accomplished, than the nitrous gas resumes its oxygen, from the continuous atmospherical current, and becomes again fit to operate a like round of transmutations with sulphurous acid, steam, and oxygen. The nitrogen (azote), which ought to be the only residuum in a _perfectly_ regulated vitriol chamber, escapes, by its relative lightness, at the opening _c_, in the roof, or, more properly speaking, is displaced by the influx of the heavier gases at the entrance-pipe.

On the intermittent plan, after the consumption of each charge, and condensation of the product, the chamber was opened, and freely ventilated, so as to expel the residuary azote, and replenish it with fresh atmospheric air. In this system there were four distinct stages or periods:--1. Combustion for two hours; 2. Admission of steam, and settling, for an hour and a half; 3. Conversion, for three hours, during which interval the drops of strong acid were heard falling like heavy hailstones on the bottom; 4. Purging of the chamber, for three quarters of an hour.

By the continuous method, sulphuric acid may be currently obtained in the chambers, of the specific gravity 1·350, or 1·450 at most; for, when stronger, it absorbs and retains permanently much nitrous acid gas; but by the intermittent, so dense as 1·550, or even 1·620; whence in a district where fuel is high priced, as near Paris, this method recommended itself by economy in the concentration of the acid. In Great Britain, and even in most parts of France, however, where time, workmen’s wages, and interest of capital, are the paramount considerations, manufacturers do not find it for their interest in general to raise the density of the acid in the chambers above 1·400, or at most 1·500; as the further increase goes on at a retarded rate, and its concentration from 1·400 to 1·600, in leaden pans, costs very little.

At about the specific gravity of 1·35, in Great Britain, the liquid of the chambers is run off, by the syphon above described, into a leaden gutter or spout, which discharges it into a series of rectangular vessels made of large sheets of lead, of 12 or 14 lbs. to the square foot, simply folded up at the angles into pans 8 or 10 inches deep, resting upon a grate made of a pretty close row of wrought-iron bars of considerable strength, under which the flame of a furnace plays. Where coals are very cheap, each pan may have a separate fire; but where they are somewhat dear, the flame, after passing under the lowest pan of the range, which contains the strongest acid (at about 1·600), proceeds upwards with a slight slope to heat the pans of weaker acid, which, as it concentrates, is gradually run down by syphons to replenish the lower pans, in proportion as their aqueous matter is dissipated. The 3 or 4 pans constituting the range are thus placed in a straight line, but each at a different level, terrace-like; _en gradins_, as the French say.

When the acid has thereby acquired the density of 1·650, or 1·700 at most, it must be removed from the leaden evaporators, because, when of greater strength, it would begin to corrode them; and it is transferred into leaden coolers, or run through a long refrigeratory worm-pipe surrounded by cold water. In this state it is introduced into glass or platinum retorts, to undergo a final concentration, up to the specific gravity of 1·842, or even occasionally 1·845, in consequence of slight saline impurities. When glass retorts are used, they are set in a long sand-bath over a gallery furnace, resting on fire tiles, under which a powerful flame plays; and as the flue gradually ascends from the fireplace, near to which it is most distant from the tiles; to the remoter end, the heat acts with tolerable equality on the first and last retort in the range. When platinum stills are employed, they are fitted into the inside of cast-iron pots, which protect the thin bottom and sides of the precious metal. The fire being applied directly to the iron, causes a safe, rapid, and economical concentration of the acid. The iron pots, with their platinum interior, filled with concentrated boiling-hot oil of vitriol, are lifted out of the fire-seat by tackle, and let down into a cistern of cold water, to effect the speedy refrigeration of the acid, and facilitate its transvasion into carboys packed in osier baskets lined with straw. Sometimes, however, the acid is cooled by running it slowly off through a long platinum syphon, surrounded by another pipe filled with cold water. _Fig._ 1102. shows my contrivance for this purpose.

The under stopcock _a_, being shut, and the leg _b_, being plunged to nearly the bottom of the still, the worm is to be filled with concentrated cold acid through the funnel _c_. If that stopcock is now shut, and _a_ opened, the acid will flow out in such quantity as to rarefy the small portion of air in the upper part of the pipe _b_, sufficiently to make the hot acid rise up over the bend, and set the syphon in action. The flow of the fluid is to be so regulated by the stopcock _a_, that it may be greatly cooled in its passage by the surrounding cold water in the vessel _f_, which may be replenished by means of the tube and funnel _d_, and overflow at _e_.

A manufacturer of acid in Scotland, who burns in each chamber 210 pounds of sulphur in 24 hours, being at the rate of 420 pounds for 20,000 cubic feet (= nearly 2000 metres cube) has a product of nearly 3 pounds of concentrated oil of vitriol for every pound of sulphur and twelfth of a pound of nitre. The advantage of his process results, I conceive, from the lower concentration of the acid in the chambers, which favours its more rapid production.

The platinum retort admits of from 4 to 6 operations in a day, when it is well mounted and managed. It has a capital of platinum, furnished with a short neck, which conducts the disengaged vapours into a lead worm of condensation; and the liquid thus obtained is returned into the lead pans. Great care must be taken to prevent any particles of lead from getting into the platinum vessel, since at the temperature of boiling sulphuric acid, the lead unites with the precious metal, and thus causes holes in the retort. These must be repaired by soldering-on a plate of platinum with gold.

Before the separate oven or hearth for burning the sulphur in contact with the nitre was adopted, this combustible mixture was introduced into the chamber itself, spread on iron trays or earthen pans, supported above the water on iron stands. But this plan was very laborious and unproductive. It is no longer followed.

One of the characters of the good quality of sulphuric acid, is its dissolving indigo without altering its fine blue colour.

Sulphuric acid, when well prepared, is a colourless and inodorous liquid, of an oily aspect, possessing a specific gravity, in its most concentrated state, of 1·842, when redistilled, but as found in commerce, of 1·845. It is eminently acid and corrosive, so that a single drop will communicate the power of reddening litmus to a gallon of water, and will produce an ulcer of the skin when allowed to remain upon it. If swallowed in its strongest state, in even a small quantity, it acts so furiously on the throat and stomach as to cause intolerable agony and speedy death. Watery diluents, mixed with chalk or magnesia, are the readiest antidotes. At a temperature of about 600° F., or a few degrees below the melting point of lead, it boils and distils over like water. This is the best method of procuring sulphuric acid free from the saline and metallic matters with which it is sometimes contaminated.

The affinity of sulphuric acid for water is so strong that, when exposed in an open saucer, it imbibes one-third of its weight from the atmosphere in 24 hours, and fully six times its weight in a few months. Hence it should be kept excluded from the air. If four parts, by weight, of the strongest acid be suddenly mixed with one part of water, both being at 50° F., the temperature of the mixture will rise to 300°; while, on the other hand, if four parts of ice be mixed with one of sulphuric acid, they immediately liquefy and sink the thermometer to 4° below zero. From the great attraction existing between this acid and water, a saucer of it is employed to effect the rapid condensation of aqueous vapour as it exhales from a cup of water placed over it; both standing under the exhausted receiver of an air-pump. By the cold produced by this unchecked evaporation in vacuo, the water is speedily frozen.

To determine the purity of sulphuric acid, let it be slowly heated to the boiling point of water, and if any volatile acid matter be present, it will evaporate, with its characteristic smell. The presence of saline impurity, which is the common one, is discovered by evaporating a given weight of it in a small capsule of platinum placed on red-hot cinders. If more than two grains remain out of 500, the acid may be reckoned to be impure. The best test for sulphuric acid, and the soluble salts into which it enters, is the nitrate of baryta, of which 182 parts are equivalent to 49 of the strongest liquid acid, or to 40 of the dry, as it exists in crystallized sulphate of potassa. One twenty thousandth part of a grain of the acid may be detected by the grayish-white cloud which baryta forms with it. 100 parts of the concentrated acid are neutralized by 143 parts of dry carbonate of potassa, and by 110 of dry carbonate of soda, both perfectly pure.

Of all the acids, the sulphuric is most extensively used in the arts, and is, in fact, the primary agent for obtaining almost all the others, by disengaging them from their saline combinations. In this way, nitric, muriatic, tartaric, acetic, and many other acids, are procured. It is employed in the direct formation of alum, of the sulphates of copper, zinc, potassa, soda; in that of sulphuric ether, of sugar by the saccharification of starch, and in the preparation of phosphorus, &c. It serves also for opening the pores of skins in tanning, for clearing the surfaces of metals, for determining the nature of several salts by the acid characters that are disengaged, &c.

According to the analysis of Dr. Thomson, the crystalline compound deposited occasionally in the leaden chambers above described consists of--

Sulphurous acid 0·6387, or 3 atoms.
Sulphuric acid 0·5290 2
Nitric acid 0·3450 1 atom.
Water 0·0733 1
Sulphate of lead 0·0140.

He admits that the proportion of water is a little uncertain; and that the presence of sulphurous acid was not proved by direct analysis. When heated with water, the crystalline matter disengages nitrous gas in abundance; lets fall some sulphate of lead; and the liquid is found to be sulphuric acid. When heated without water, it is decomposed with emission of nitrous gas and fuming nitric acid; leaving a liquid which, mixed with water, produces a brisk effervescence, consisting chiefly of nitrous gas.

The following TABLE shows the quantity of concentrated and dry sulphuric acid in 100 parts of dilute, at different densities, by my experiments, published in the Quarterly Journal of Science, for October, 1817:--

+-------+---------+-------+
|Liquid.|Sp. grav.| Dry. |
+-------+---------+-------+
| 100 | 1·8460 |81·54 |
| 99 | 1·8438 |80·72 |
| 98 | 1·8415 |79·90 |
| 97 | 1·8391 |79·09 |
| 96 | 1·8366 |78·28 |
| 95 | 1·8340 |77·46 |
| 94 | 1·8288 |76·65 |
| 93 | 1·8235 |75·83 |
| 92 | 1·8181 |75·02 |
| 91 | 1·8026 |74·20 |
| 90 | 1·8070 |73·39 |
| 89 | 1·7986 |72·57 |
| 88 | 1·7901 |71·75 |
| 87 | 1·7815 |70·94 |
| 86 | 1·7728 |70·12 |
| 85 | 1·7640 |69·31 |
| 84 | 1·7540 |68·49 |
| 83 | 1·7425 |67·68 |
| 82 | 1·7315 |66·86 |
| 81 | 1·7200 |66·05 |
| 80 | 1·7080 |65·23 |
| 79 | 1·6972 |64·42 |
| 78 | 1·6860 |63·60 |
| 77 | 1·6744 |62·78 |
| 76 | 1·6624 |61·97 |
| 75 | 1·6500 |61·15 |
| 74 | 1·6415 |60·34 |
| 73 | 1·6321 |59·52 |
| 72 | 1·6204 |58·71 |
| 71 | 1·6090 |57·89 |
| 70 | 1·5975 |57·08 |
| 69 | 1·5868 |56·26 |
| 68 | 1·5760 |55·45 |
| 67 | 1·5648 |54·63 |
| 66 | 1·5503 |53·82 |
| 65 | 1·5390 |53·00 |
| 64 | 1·5280 |52·18 |
| 63 | 1·5170 |51·37 |
| 62 | 1·5066 |50·55 |
| 61 | 1·4960 |49·74 |
| 60 | 1·4860 |48·92 |
| 59 | 1·4760 |48·11 |
| 58 | 1·4660 |47·29 |
| 57 | 1·4560 |46·48 |
| 56 | 1·4460 |45·66 |
| 55 | 1·4360 |44·85 |
| 54 | 1·4265 |44·03 |
| 53 | 1·4170 |43·22 |
| 52 | 1·4073 |42·40 |
| 51 | 1·3977 |41·58 |
| 50 | 1·3884 |40·77 |
| 49 | 1·3788 |39·95 |
| 48 | 1·3697 |39·14 |
| 47 | 1·3612 |38·32 |
| 46 | 1·3530 |37·51 |
| 45 | 1·3440 |36·69 |
| 44 | 1·3345 |35·88 |
| 43 | 1·3255 |35·06 |
| 42 | 1·3165 |34·25 |
| 41 | 1·3080 |33·43 |
| 40 | 1·2999 |32·61 |
| 39 | 1·2913 |31·80 |
| 38 | 1·2826 |30·98 |
| 37 | 1·2740 |30·17 |
| 36 | 1·2654 |29·35 |
| 35 | 1·2572 |28·54 |
| 34 | 1·2490 |27·72 |
| 33 | 1·2409 |26·91 |
| 32 | 1·2334 |26·09 |
| 31 | 1·2260 |25·28 |
| 30 | 1·2184 |24·46 |
| 29 | 1·2108 |23·65 |
| 28 | 1·2032 |22·83 |
| 27 | 1·1956 |22·01 |
| 26 | 1·1876 |21·20 |
| 25 | 1·1792 |20·38 |
| 24 | 1·1706 |19·57 |
| 23 | 1·1626 |18·75 |
| 22 | 1·1549 |17·94 |
| 21 | 1·1480 |17·12 |
| 20 | 1·1410 |16·31 |
| 19 | 1·1330 |15·49 |
| 18 | 1·1246 |14·68 |
| 17 | 1·1165 |13·86 |
| 16 | 1·1090 |13·05 |
| 15 | 1·1019 |12·23 |
| 14 | 1·0953 |11·41 |
| 13 | 1·0887 |10·60 |
| 12 | 1·0809 | 9·78 |
| 11 | 1·0743 | 8·97 |
| 10 | 1·0682 | 8·15 |
| 9 | 1·0614 | 7·34 |
| 8 | 1·0544 | 6·52 |
| 7 | 1·0477 | 5·71 |
| 6 | 1·0405 | 4·89 |
| 5 | 1·0336 | 4·08 |
| 4 | 1·0268 | 3·26 |
| 3 | 1·0206 | 2·446 |
| 2 | 1·0140 | 1·63 |
| 1 | 1·0074 | 0·8154|
+-------+---------+-------+

SUMACH (Eng. and Fr.; _Schmack_, Germ.); is the powder of the leaves, peduncles, and young branches of the _Rhus coriaria_, and _Rhus cotinus_, shrubs which grow in Hungary, the Bannat, and the Illyrian provinces. Both kinds contain tannin, with a little yellow colouring-matter, and are a good deal employed for tanning light-coloured leathers; but the first is the best. With mordants, it dyes nearly the same colours as galls. In calico-printing, sumach affords, with a mordant of tin, a yellow colour; with acetate of iron, weak or strong, a gray or black; and with sulphate of zinc, a brownish-yellow. A decoction of sumach reddens litmus paper strongly; gives white flocks with the protomuriate of tin; pale-yellow flocks with alum; blue flocks with red sulphate of iron, with an abundant precipitate. In the south of France, the twigs and leaves of the _Coriaria myrthifolia_ are used for dyeing, under the name of _rédoul_, or _rodou_.

SWEEP-WASHER, is the person who extracts from the sweepings, potsherds, &c., of refineries of silver and gold, the small residuum of precious metal.

SYNTHESIS, is a Greek word, which signifies combination, and is applied to the chemical action which unites dissimilar bodies into a uniform compound; as sulphuric acid and lime, into gypsum; or chlorine and sodium, into culinary salt.

SYRUP, is a solution of sugar in water. Cane-juice, concentrated to a density of 1·300, forms a syrup which does not ferment in the transport home from the West Indies, and may be boiled and refined at one step into superior sugar-loaves, with eminent advantage to the planter, the refiner, and the revenue.

T.

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:--

+----------------------------------+--------+----------+-------------+
| Substances. |In 480, |In about |In 100 parts,|
| |by Davy.|8 oz., by |by Cadet de |
| | |Biggins. |Gassincourt. |
+----------------------------------+--------+----------+-------------+
|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 | |
| Do. Common willow | 11 |boughs, 31| |
|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.

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.