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LoNDON ENCYCLOPEDIA,

or

UNIVERSAL DICTIONARY

SCIENCE, ART, LITERATURE, AND PRACTICAL MECHANICS,

coni prisi NG A

POPULA) VIEW OF THE PRESENT STATE OF KNOWLEDGE.

illustrated by

NJMEROUS ENGRAVINGS, A GENERAL ATLAS,

AND Appropriate di AGRAMs.

sic oportet ad librumbresertim miscellanei generis, legendum accedere lectorem, ut solet ad convivium conviva civilis.
convivator annititur omnisatisfacere; et tamen si quid apponitur, quod hujus aut illius palato non respondeat, et hic et ille
urbane dissimulant, et alia ula probant, ne quid contristent convivatorem. Erasmus.

A reader should “it down a book, especially of the miscellaneous kind, as a well-behaved visitor does to a banquet. The
master of the seast exerts holf to satisfy his guests; but if, after all his care and pains, something should appear on the table

that does not suit this or thatson's taste, they politely pass it over without notice, and commend other dishes, that they inay not
distrees a kind host. Translation.

by the ORIGINAL DITOR OF THE ENCYCLOPAEDIA METROPOLITANA,

Assist BY EMIN ENT PROFEssion Al AND oth ER GENtleMEN.

IN TWENTY-TV () VOLUMES.

- VOL. XVIII.

——

LONDON :

PRINTED THOMAS TEGG, 73, CHEAPSIDE;

solo by N. HAILES, PiCCADILl E. wilson, Roy Al Exchange ; J. MAson, city Road :
- BOWD & KERBY, Oxford street:
GotifFIN & co. Glasgow: J. cuxo, publin : M. Baudry, paris: F. fleischer, Leipsic:
AND whippi Law Rence, SALEM, North AMERICA.

1829.

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Sandys. Toad that under the cold stone Sweltered, venom sleeping got ; Boil thou first i' th' charmed pot. Shakspeare.

But that I think his father loves him not, I'd have him poisoned with a pot of ale. Id. My thoughts are whirled like a potter's who, I learnt it in England, where they are most potent in Potting. Id. Othello. Thou best of gold art worst of gold, Other less fine in carat is more precious, Preserving life in medicine potable. Shakspeare. If I had a thousand sons, the first human principle I would teach them, should be to forswear thin potations, and to addict themselves to sack. Id. Henry IV. At this day at Gaza, they couch potsherds of vessels of earth in their walls to gather the wind from the top, and it in spouts into rooms. P pass P Bacon's Natural History. Dig a pit upon the sea shore, somewhat above the high-water mark; and sink it as deep as the lowwater mark; and, as the tide cometh in, it will fill with water fresh and potable. Bacon. The said potable gold should be endued with a capacity of being agglutinated and assimilated to the innate heat. Harvey. Rivers run potable gold. Milton's Paradise Lost. Gigantic minds, as soon as work was done, To their huge pots of boiling pulse would run, Fell to with eager joy. Dryden. Potted fowl and fish come in so fast, That ere the first is out the second stinks, And mouldy mother gathers on the brinks. Id. Whence come broken potsherds tumbling down, And leaky ware from garret windows thrown : Well may they break our heads. Id. Some press the plants with sherds of potter's o:

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Let me see her Arabian pothooks. Id. The sheep went first to pot, the goats next, and after them the oxen, and all little enough to keep life together. - L’Estrange. ..Whenever potters meet with any chalk or marl mixed with their clay, though it will with the clay hold burning, yet, whenever any water comes near any such pots after they are burnt, both the chalk and marl will slack and spoil their ware. Mortimer. Acorns, mast, and other seeds may be kept well, by being barrelled or potted up with moist sand. Id. A potter will not have any chalk or marl mixed with the clay. Id. Husbandry. Pot them in natural, not forced earth; a layer of rich mould beneath and about this natural earth to nourish the fibres, but not so as to touch the bulbs. Evelyn. Where solar beams Parch thirsty human veins, the damasked meads Unforced display ten thousand painted flowers Useful in potables. - Philips. Sir Tristram telling us tobacco was a potherb, bid

the drawer bring in to other half pint. Tatler.
Suppose ão eyes sent equal rays
Upon two distant pots of ale,
Not knowing which was mild or stale. Prior.
He like the potter in a mould has cast
The world's great fame. Id.

John's ready money went into the lawyers' pockets; then John began to borrow money upon the bank stock, now and then a farm went to pot. Arbuthnot's History of John Bull. Of alimentary leaves, the olera or potherbs afford an excellent nourishment; amongst those are the cole or cabbage kind. Arbuthnot. The columella is a fine, thin, light, bony tube, the bottom of which spreads about, and gives it the resemblance of a wooden potlid in country houses. Derham. A soldier drinks his pot, and then offers payment. - Swift. Leaves eaten raw are termed sallad; if boiled, they become potherbs; and some of those plants which are pot-herbs in one family, are sallads in another. Is atts. For great the man, and useful, without doubt, Who seasons pottage, or expels the gout; Whose science keeps life in, and keeps death out. Harte.

POTAGER, n. s. From Pottage. A por. ringer.

An Indian dish or potager, made of the bark of a tree, with the sides and rim sewed together after the manner of twiggen-work. Grew's Museum.

POTAMOGETON, pond weed, a genus of the tetragynia order, and tetrandria class of plants; natural order fifteenth, inundatae: cal. none; petals four ; no style, and four seeds. There are twelve species, all of them vegetables floating on the surface of stagnant waters, affording agreeable shade to fish, and food to cattle.

B

POTAMON, or PotAMo, a philosopher of Alexandria. He attached himself to none of the schools of philosophy of his time; but kept a middle course between the scepticism of the Pyrrhonians and the presumption of the dogmatists. He was the first projector of the Eclectic sect; for, though their mode of philosophising had been common before, he was the first that attempted to institute a new sect on this principle.’ ‘Diogenes Laertius relates that, not long before he wrote his Lives of the Philosophers, an Eclectic sect, sk\exruka ric apsaic, had been introduced by Potamo of Alexandria, who se

lected tenets from every former sect. Suidas and Porphyry also mention him. The time when Potamo flourished is uncertain. Suidas

places him under Augustus: but it is more probable, from the account of Laertius, that he flourished about the close of the second century.’ POTAR'GO, n.s. Ital. potarge. A West Indian pickle. What lord of old would bid his cook prepare Mangos, potargo, champignons, cavarre : King. POTASH, m. s. Fr. potasse. The vegetable alkali. See below. Cheshire rock-salt, with a little nitre, allum, and potash, is the flux used for the running of the plateglass. Woodward. Potash, or PotAssa, in chemistry and the manufactures, more commonly known as the vegetable alkali, is a fixed alkaline salt obtained from the ashes of burnt vegetables of various kinds. The method of making potash is described by Dr. Shaw as follows:—Burn a quantity of billet wood to gray ashes; and, taking several pounds of these ashes, boil them in water, so as to make a very strong lixivium or lie. Let this lie be strained through a coarse linen cloth, to keep out any parts of half-burnt wood that might happen to remain in the ashes; then evaporate this strained lie in an iron pan, over a quick fire, almost to dryness: then, taking out the matter remaining at the bottom, and putting it into an iron crucible, set it in a strong fire till the matter is melted, and then immediately pour it out upon an iron plate, where it soon cools, and appears in the form of a solid lump of potash. In this manner potash is made in the large way of business, for the service of the soap-boiler, glassmaker, fuller, &c.; but, according to the difference of the wood, or combustible matter employed, with the manner of turning it, and conducting the process, different kinds of potash are prepared. There are certain saline plants that yield this potash to great advantage, as particularly the plant kali; there are others that af. ford it in less plenty, and of an inferior quality, as bean-stalks, &c.; but, in general, all vegetable subjects afford it of one kind or other, and may most of them be made to yield it tolerably perfect after the manner of the process already laid down, even the loppings, roots, and refuse parts of ordinary trees, vine-clippings, &c. It was announced in the philosophical Journals that, in France, potash had been obtained in great quantities from potato stalks. In order to put this to the test of experiment, Sir John Hay and Dr. M'Culloch made a trial on a large scale, and found that the quantity of potash was

so small that no person could be remunerated by it for the trouble of the process. Messrs. Tay. lors of Queensferry, by desire of Sir John Hay, made an experiment on the produce of two acres of potato stalks, which yielded two casks of ashes, weighing 2 cwt. 23 lbs., which produced of soluble substance only 36 lbs., containing a great deal of muriate of potash and sulphate of potash. The value of this produce was not more than 24. per lb., or 6s. in all; and on twelve acres of their own they had a similar result. The following is a table of the saline product of 1000 lbs. of ashes of the following vegetables:—

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On these tables Kirwan makes the following remarks:–1. That in general weeds yield more ashes, and their ashes much more salt, than woods ; and that consequently, as to salts of the vegetable alkali kind, as potash, pearl-ash, cashup, &c., neither America, Trieste, nor the northern countries, have any advantage over Ireland. 2. That of all weeds fumitory produces most salt, and next to it wormwood. But, if we attend only to the quantity of salt in a given weight of ashes, the ashes of wormwood contain most. Trifolium fibrinum also produces more ashes and salt than fern. Dr. John of Berlin observes that uncombined potash does not occur in living vegetables, it being always combined with an acid, and is only found in them when they are in a state of putridity or decomposition. Plants that feel rough and sharp, particularly equiseti, contain much siliceous earth; in the latter full thirteen per cent. Lichens that grow on the summits of fir trees contain an uncommon proportion of oxide of iron, which, Dr. John remarks, may be viewed as illustrative of the formation of iron by the vegetable process. Dr. John recommends the use of decaying and diseased wood to those who wish to obtain potash from it by burning, as he maintains that the quantity of potash is much increased by the putrefactive process. This remark is not new; for we find it mentioned in the second volume of Schreber's Sammlung verschiedener Schriften, published in 1763, that putrid wood was recommended for obtaining ashes in preference to fresh wood. Plants, which were allowed to grow in a solution of natron, absorbed by their roots a considerable portion of the alkali; but none of this appeared when the ashes of the plant were examined: in

place of it appeared potash; and hence it is conjectured that vegetables have the power of converting natron into potash.

The process for * pot and pearl-ash is given by Kirwan as follows:—

1. The weeds should be cut just before they seed, then spread, well dried, id gathered clean.

2. They should be burned within doors on a grate, and the ashes laid in a chest as fast as they are produced. If any charcoal be visible, it should be picked out, and thrown back into the fire. If the weeds be moist, much coal will be found. A close smothered fire, which has been recommended by some, is very prejudicial.

3. They should be lixiviated with twelvetimes

their weight of boiling water. A drop of the solution of corrosive sublimate will immediately discover when the water ceases to take up any more alkali. The earthy matter that remains is said to be a good manure for clayey soils. 4. The lie thus formed should be evaporated to dryness in iron pans. Two or three at least of these should be used, and the lie, as fast as it is concreted, passed from the one to the other. Thus, much time is saved, as weak lies evaporate more quickly than the stronger. The salt thus produced is of a dark color, and contains much extractive matter; and, being formed in iron pots, is called potash. 5. This salt should then be carried to a reverberatory furnace, in which the extractive matter is burnt off, and much of the water dissipated: hence it generally loses from ten to fifteen per cent. of its weight. Particular care should be taken to prevent its melting, as the extractive matter would not then be perfectly consumed, and the alkali would form such a union with the earthy parts as could not easily be dissolved. Kirwan adds this caution, because Dr. Lewis and Mr. Dossie have inadvertently directed the contrary. This salt, thus refined, is called pearlash, and must be the same as the Dantzic pearl-ash, To obtain this alkali pure, Berthollet recommends to evaporate a solution of potash, made caustic by boiling with quicklime, till it becomes of a thickish consistence; to add about an equal weight of alcohol, and let the mixture stand some time in a close vessel. Some solid matter, partly crystallised, will collect at the bottom; above this will be a small quantity of a dark-colored fluid; and on the top another lighter. The latter, separated by decantation, is to be evaporated quickly in a silver basin in a sand-heat. Glass, or almost any other metal, would be corroded by the potash. Before the evaporation has been carried far, the solution is to be removed from the fire, and suffered to stand at rest; when it will again separate into two fluids. The lighter, being poured off, is again to be evaporated with a quick heat; and, on standing a day or two in a close vessel, it will deposit transparent crystals of pure potash. If the liquor be evaporated to a pellicle, the potash will concrete without regular crystallisation. In both cases a high-colored liquor is separated, which is to be poured off; and the potash must be kept carefully secluded from air Its taste is remarkably acrid, and it is so exceedingly corrosive that, when applied to any

part of the body, it destroys it almost instantaneously. On account of this property it has been called caustic, and is often used by surgeons to open abscesses, and destroy useless or hurtful excrements. When heated it melts. At a red heat it swells, and evaporates slowly in a white acrid smoke. When exposed to the air it soon attracts moisture, and is converted into a liquid; and combines with carbonic acid, for which it has a great affinity. It has a very strong affinity for water. At the common temperature of the air, one part of water dissolves two parts of potassa. e solution is transparent, very dense, and almost of the consistence of oil. In this state it is usually employed by chemists. When four parts of potash in powder, and one of snow are mixed together, the mixture becomes liquid, and absorbs a quantity of caloric. This mixture was employed by Lowitz to produce artificial cold. When the aqueous solution of potash is evaporated to a proper consistency, the potash crystallises. The shape of its crystals is very different, according to the way in which they have been produced. When allowed to form in the cold, they are octahedrons in groups, and contain 0.43 of water: when formed by evaporation on the fire, they assume the figure of very thin transparent blades of extraordinary magnitude, which, by an assemblage of lines crossing each other in prodigious numbers, present an aggregate of cells or cavities, commonly so very close that the vessel may be inverted without losing one drop of the liquid it contains. Potash is not altered by exposure to the light. A perfectly pure solution of potash will remain transparent on the addition of lime-water, show no effervescence with dilute sulphuric acid, and not give any precipitate on blowing air from the lungs through it by means of a tube. Pure potash for experimental purposes may most easily be obtained by igniting cream of tartar in a crucible, dissolving the residue in water, filtering, boiling with a quantity of quick

lime, and, after subsidence, decanting the clear

liquid, and evaporating in a loosely covered silyer capsule, till it flows like oil, and then pouring it out on a clean iron plate. A solid white cake of pure hydrate of potash is thus obtained, without the agency of alcohol. It must be immediately broken into fragments, and kept in a well-stoppered phial.

As 100 parts of subcarbonate of potash are equivalent to about seventy of pure concentrated oil of vitriol, if into a measure tube, graduated into 100 equal parts, we introduce the seventy grains of acid, and fill up the remaining space with water, then we have an alkalimeter for estimating the value of commercial pearl-ashes, which, if pure, will require for 100 grains 100 divisions of the liquid to neutralise them. If they contain only sixty per cent. of genuine subcarbonate, then 100 grains will require only sixty divisions, and so on. When the alkalimeter indications are required in pure or absolute potash, such as constitutes the basis of nitre, then we must use 102 grains of pure oil of vitriol, along with the requisite bulk of water to fill up the volume of the graduated tube.

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