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The hydrate of potash, as obtained by the preceding process, is solid, white, and extremely caustic ; in minute quantities, changing the purple of violets and cabbage to a green, reddened litmus to purple, and yellow turmeric to a reddish-brown. It rapidly attracts humidity from the air, passing into the oil of tartar per deliquium of the chemists; a name, however, also given to the deliquesced subcarbonate. Charcoal applied to the hydrate of potash at a cherry-red heat gives birth to carburetted hydrogen, and an alkaline subcarbonate; but, at a heat bordering on whiteness, carburetted hydrogen, carbonous oxide, and potassium are formed. Several metals decompose the hydrate of potash, by the aid of heat; particularly potassium, sodium, and iron. The fused hydrate of potash consists of 6 protoxide of potassium + 1.125 water = 7-125, which number represents the compound prime equivalent. It is used in surgery as the }. cautery for forming eschars; and it was ormerly employed in medicine diluted with broths as a lithontriptic. In chemistry it is very extensively employed, both in manufactures and as a reagent in analyses. It is the basis of all the common soft soaps. Dr. Wollaston has recently ascertained the existence of potash in sea-water. He estimates the proportion of this alkali, which he supposes to exist in the state of sulphate, at something less than oath part of the water, at its average density. Ise has also detected traces of potash in the water of the lake of Ourmia or Arumea, which is unconnected with the ocean. The water of this lake (which is situated on the province of Azerbijan in Persia) is said to be salter than that of the sea, so that no fish can live in it. Potash, until Sir Humphry Davy's memorable discovery of its chemical nature, was considered as a simple body, though strong suspicions were entertained of its being of a compound nature. From that philosopher's researches, however, potash appears to consist of a metallic basis,

which he called potassium, united with oxygen,

in the following proportions:— 83

Potassium . - Oxygen • . . 17 100

POTASSIUM, in chemistry, the name given by Sir H. Davy to the metallic base of potash, discovered by him in 1807. Till this period potash and soda were necessarily regarded as simple from the impossibility of decomposing them by any known methods. Yet they were generally suspected to be compounds, though no chemist was able to detect their elements. By many the alkalescent principle was supposed to be nitrogen, as the acidifiable was oxygen. Morveau and Desormes published an ingenious set of experiments, in which they endeavoured to prove that potash was a compound of hydrogen and lime. Parracq, however, with that accuracy which has characterised most of his enquiries, soon disproved this theory, and evinced that the results obtained by Desormes and Morveau were owing, in most cases, to the impurity of the

potash with which they had made their experiments; while in others they had drawn wrong inferences from mistaken resemblances. As soon as voltaic electricity was so far rendered manageable as to be applied with very great power to chemical analyses, Mr. Dav conceived the idea of enlisting this wonderful agency into his service, with a view of endeavouring to obtain a decomposition of the alkalies; and he was the more fully induced to give a full scope and latitude to a series of experiments of this kind from observing that if a neutral substance, or a compound of an acid and an alkali, constituted a part of the voltaic circle, a decomposition of such substance was the result, the acid alone always travelling to the positive side of the chain and the alkali to the negative. In the first attempts which Sir H. Davy made for the decomposition of the fixed alkalies, he entirely failed, in consequence of his having acted upon their aqueous solutions only. He afterwards used potash in the state of igneous fusion, and acted upon it by an electrical power, which was produced from a galvanic battery of 100 plates of six inches square, highly charged. Here some brilliant phenomena were produced. A most intense light and a column of flame were exhibited, which seemed to be owing to the development of combustible matter; and when the order was changed, so that the alkali was brought in contact with the negative side of the battery, aériform globules, which inflamed in the atmosphere, rose through the potash. Being, however, unable to collect the products of decomposition by this means, he had then recourse to pure potash in its usual state, and depended on electricity alone for its fusion, as well as its decomposition. A small piece of pure potash, moistened a little by the breath, was placed upon an insulated disc of platinum, connected with the negative side of a battery consisting of 100 plates of six inches and 150 of four inches square, in a state of intense activity, and a platinum wire, communicating with the positive side, was brought in contact with the upper surface of the alkali. Under these circumstances, a vivid action soon commenced. The potash began to fuse at both its points of electrisation, and small globules, having a high metallic lustre and precisely similar in visible characters to quicksilver, appeared, some of which burnt with explosion and bright flame. These globules, which appeared to be metallic, were the basis of potash. If iron turnings be heated to whiteness in a curved gun-barrel, and potash be melted and made slowly to come in contact with the turnings, air being excluded, potassium will be formed, and will collect in the cool part of the tube. This method of procuring it was discovered by M. M. Gay Lussac and Thenard in 1808. It may likewise be produced by igniting potash with charcoal, as M. Curaudau showed the same year. M. Brunner, by acting on calcined tartar in a bottle of wrought iron, has succeeded in obtaining potassium at a comparatively moderate heat. The bottle is spheroidal, about half an inch in thickness, and capable of holding about a pint of water; a bent gun-barrel of ten or twelve inches in length screws into the mouth of the bottle. The bottle, well luted over with fire-clay, is set in a strong air furnace, so that the tube may dip down externally beneath the surface of naphtha contained in a cylindric copper vessel, standing in a tub containing ice and water. The top of the naphtha vessel has a cover fixed on it. pierced with a hole to receive the end of the gun-barrel; and, from the side of the upper part of the vessel, a small tube goes off at right angles to let the air and vapors escape. It is advantageous to mix a little ground charcoal with the tartar previously calcined in a covered vessel, in the same iron bottle for example. Nearly 300 grains of potassium have been procured by this apparatus from twenty-four ounces of crude tartar.—Bibliotheque Universelle, xxii. 36. Potassium is possessed of very extraordinary properties. It is lighter than water, its specific gravity being 0-865 to water 1:0. At common temperatures it is solid, soft, and easily moulded by the fingers. At 150° Fahrenheit it fuses, and in a heat a little below redness it rises in vapor. It is perfectly opaque. When newly cut, its color is splendent white, like that of silver, but it rapidly tarnishes in the air. To preserve it unchanged, we must enclose it in a small phial, with pure naphtha. It conducts electricity like the common metals. When thrown upon water, it acts with great violence, and swims upon the surface, burning with a beautiful light of a red color, mixed with violet. The water becomes a solution of pure potash. When moderately heated in the air, it inflames, burns with a red light, and throws off alkaline fumes. Placed in chlorine, it spontaneously burns with great brilliancy. On all fluid bodies which contain water, or much oxygen or chlorine, it readily acts; and in its general powers of chemical combination, says its illustrious discoverer, potassium may be compared to the alkahest, or universal solvent, imagined by the alchemists. Potassium combines with oxygen in different proportions. When potassium is gently heated in common air, or in oxygen, the result of its combustion is an orange-colored fusible substance. For every grain of the metal consumed, about one cubic inch and seven-tenths of oxygen are condensed. To make the experiment accurately, the metal should be burned in a tray of platina covered with a coating of fused muriate of potash. e substance procured by the combustion of Totassium at a low temperature, was first observed in October 1807, by Sir Humphry Davy, who supposed it to be the protoxide; but M. M. Gay Lussac and Thenard, in 1810, showed that it was in reality the deutoxide, or peroxide. When it is thrown into the water, oxygen is evolved, and a solution of the protoxide results, constituting common aqueous potash. When it is fused, and brought in contact with combustible bodies, they burn vividly, by the excess of its oxygen. If it be heated in carbonic acid, oxygen is disengaged, and common subcarbonate of potash is formed. Then it is heated very strongly upon latina,

. gas is expelled from it, and there remains ifficultly fusible substance of a gray color, vitreous fracture, soluble in water without effervescence, but with much heat. Aqueous potash is produced. The above ignited solid is protoxide of potassium, which becomes pure potash by combination with the equivalent quantity of water. When we produce potassium with ignited iron-turnings and potash, much hydrogen is disengaged from the water of the hydrate, while the iron becomes oxidised from the residuary oxygen. By heating together pure hydrate of potash and boracic acid, Sir H. Davy obtained from seventeen to eighteen of water from 100 parts of the solid alkali. - By acting on potassium with a very small quantity of water, or by heating potassium with fused potash, the protoxide may also be obtained. The proportion of oxygen in the protoxide is determined by the action of potassium upon water. Eight grains of potassium produce from water about nine cubic inches and a half of hydrogen; and for these the metal must have fixed four cubic inches and three quarters of oxygen. But as 100 cubic inches of oxygen weigh 33.9 gr. 4} will weigh 1-61. Thus, 9.61 gr. of the protoxide will contain eight of metal; and 100 will contain 83.25 metal + 16-75 oxygen. From these data, the prime of potassium comes out 4:969; and that of the protoxide 5:969. Sir H. Davy adopts the number 75 for potassium, corresponding to 50 on the oxygen scale. When potassium is heated strongly in a small quantity of common air, the oxygen of which is not sufficient for its conversion into potash, a substance is formed of a grayish color, which, when thrown into water, effervesces without taking fire. It is doubtful whether it be a mixture of the protoxide and potassium, or a combination of potassium with a smaller proportion of oxygen than exists in the protoxide. In this case it would be a suboxide, consisting of 2 primes of potassium = 10, + 1 of oxygen - 11. When thin pieces of potassium are introduced into chlorine, the inflammation is very vivid; and, when potassium is made to act on chloride of sulphur, there is an explosion. The attraction of chlorine for potassium is much stronger than the attraction of oxygen for the metal. Both of the oxides of potassium are immediately decomposed by chlorine, with the formation of a fixed chloride, and the extrication of oxygen. The combination of potassium and chlorine is the substance which has been improperly called muriate of potash, and which in common cases, is formed by causing liquid muriatic acid to saturate solution of potash, and then evaporating the liquid to dryness and igniting the solid residuum. The hydrogen of the acid here unites to the oxygen of the alkali, forming water, which is exhaled; while the remaining chlorine and potassium combine. It consists of 5 potassium + 4.5 chlorine. Potassium combines with hydrogen, to form potassureted hydrogen, a spontaneously inflammable gas, which comes over occasionally in the production of potassium by the gun-barrel experipient. M.M. Gay Lussac and Thenard describe

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also a solid compound of the same two ingredients, which they call a hydruret of potassium. It is formed by heating the metal a long while in the gas, at a temperature just under ignition. They describe it as a grayish solid, giving out its hydrogen on contact with mercury. When potassium and sulphur are heated together, they combine with great energy, with disengagement of heat and light even in vacuo. The resulting sulphuret of potassium is of a dark gray color. It acts with great energy on water, producing sulphureted hydrogen, and burns brilliantly when heated in the air, becoming sulphate of potash. It consists of 2 sulphur + 5 potassium, by Sir H. Davy's experiments. Potassium has so strong an attraction for sulphur that it rapidly separates it from hydrogen. If the potassium be heated in the sulphureted gas, it takes fire and burns with great brilliancy; sulphuret of potassium is formed, and pure hydrogen is set free. Potassium and phosphorus enter into union with the evolution of light; but the mutual action is feebler than in the preceding compound. The phosphuret of potassium, in its common form, is a substance of a dark chocolate color, but when heated with potassium in great excess it becomes of a deep gray color, with considerable lustre. Hence it is probable that phosphorus and potassium are capable of combining in two proportions. The phosphuret of potassium burns with great brilliancy when exposed to air, and when thrown into water produces an explosion, in consequence of the immediate disengagement of phosphureted hydrogen. Charcoal which has been strongly heated in contact with potassium effervesces in water, rendering it alkaline, though the charcoal may be previously exposed to a temperature at which potassium is volatilised. Hence there is probably a compound of the two formed by a feeble attraction. Of all known substances, potassium is that which has the strongest attraction for oxygen; and it produces such a condensation of it, that the oxides of potassium are denser than the metal itself. Potassium has been skilfully used by Sir H. Davy and MM. Gay Lussac and Thenard, for detecting the presence of oxygen in bodies. A number of substances, undecomposable by other chemical agents, are readily decomposed by this substance. When a globule is placed upon ice, not even the solid form of both the substances can prevent their union; for the metalloid instantly burns with a bright flame, and a deep hole is made in the ice, which is found to contain a solution of potash. When a globule is dropped upon moistened turmeric paper, it instantly burns, and moves rapidly upon the o: as if in search of moisture, leaving behind it a deep reddish brown trace. So strong is the attraction of the basis of potash for oxygen, that it disco. vers and decomposes the small quantities of water contained in alcohol and ether, even when they are carefully purified. POTATO, n.s. An American word, battata originally. See below. An esculent root.

On choicest melons and sweet grapes they dine, And with potatoes fat their wanton swine. Waller. Leek to the Welch, to Dutchmen butter's dear, Of Irish swains potatoe is the chear; Oats for their feasts the Scottish shepherds grind, Sweet turnips are the food of j ; While she loves turnips butter I'll despise, Nor leeks, nor oatmeal, nor potatoe prize. Gay. The families of farmers live in filth and nastiness upon buttermilk and potatoes. Swift. The red and white potatoes are the most common esculent roots now in use, and were originally brought from Virginia into Europe. Miller. Potato, in botany. See Solan UM. Potatoes came originally from North America, where they were not reckoned good for food. They were first introduced into Ireland in 1565, and thence into England by a vessel wrecked on the western coast, at North Meols, in Lancashire, a place and soil still famous for producing this vegetable in great perfection. It was forty years after their introduction, however, before they were much cultivated about London; and then they were considered as rarities, without any conception of the utility that might arise from bringing them into common use. At this time they were distinguished from the Spanish by the name of Virginia potatoes, or battatas, which is the Indian name of the Spanish sort. At a meeting of the Royal Society, March 18th, 1662-3, a letter was read from Mr. Buckland, a Somerset gentleman, recommending the planting of potatoes in all parts of the kingdom to prevent famine. This was referred to a committee; and, in consequence of their report, Mr. Buckland had the thanks of the society; such members as had lands were entreated to plant them, and Mr. Evelyn was desired to mention the proposals at the close of his Sylva. In Sweden, notwithstanding the indefatigable industry of Linnaeus, the culture of potatoes was only introduced in 1764, when a royal edict was published to encourage their general cultivation. They were known there, however, at an earlier period; for, in the Memoirs of the Royal Academy of Sciences in Sweden, 1747, M. Charles Skytse proposed to distil brandy from them, in order to save corn, which in that country is very dear. He found that an acre of land set with potatoes will yield a much greater quantity of brandy than wi. sown with barley. The utility of potatoes is well known, and this utility has brought them into general use, and has extended them over every part of this kingdom. To promote this utility, and to make their cultivation more easy, a variety of experiments and inquiries have been made. See RURAL Economy. POTCH, v. a. Fr. pocher. To thrust out the eyes as with a thumb. To thrust; push. Where I thought to crush him in an equal force, True sword to sword; I'll potch at him some way, Or wrath or craft may get him. Shakspeare. Porch, v. a. Fr. pocher. To poach; to boil slightly. Commonly written PoAch, which See. In great wounds, it is necessary to observe a spare diet, as panadoes or a potched egg; this much availing to prevent inflammation. Wiseman's Surgery.

POTEMKIN (George, Prince), a descendant of a Polish family, who entered into the service of Russia, and distinguished himself so much as to be appointed to the chief command by Catharine II. On the 17th December, 1788, he took the important fortress of Oczakow from the Turks, and obtained several other victories over them. The empress rewarded his services by loading him with riches and honors: and it is said that she intended to have made him sovereign of that part of his native country which she had dismembered, when he died in 1791, aged fifty-two.

POTENCY, n.s.

Po'TENT, adj.

Lat. potentia, potens." Power; efficacy; autho

Po'TENTATE, rity: * is powerful;

Po TENTLY. forcible; strong; efficacious: potentate, a possessor of sovereign power: potently follows the senses of potent.

There is nothing more contagious than some kinds of harmony; than some nothing more strong and Potent unto good. Hooker. Now arriving At place of potency and sway o' the state, If he should still malignantly remain Fast foe to the plebeians, your voices might Be curses to yourselves. Shakspeare. Coriolanus. Use can master the devil, or throw him out With wonderous potency. Shakspeare. Hamlet. I do believe, Induced by potent circumstances, that You are mine enemy. Id. Henry VIII. Why stand these royal fronts amazed thus 2 Cry havock, kings' back to the stained field, You equal potents, fiery kindled spirits! Shakspeare. You are potently opposed; and with a malice Of as great size. Shakspeare. Henry VIII. Kings and mightiest potentates must die. Shakspeare. By what name shall we call such an one, as exceedeth God in potency? Raleigh. Metals are hardened by often heating and quenching; for cold worketh most potently upon heat precedent. Bacon. One would wonder how, from so differing premises, they should infer the same conclusion, were it not that the conspiration of interest were too potent for the diversity of judgment. Decay of Piety. These defences are but compliments,

To dally with confining potentates. Daniel. When by command

Moses once more his potent rod extends

Over the sea; the sea his rod obeys. Milton.

All obeyed the superior voice Of their great potentate ; for great indeed His name, and high was his degree in lawn, d. We acknowledge all power derived from him, and depending on his pleasure : we ascribe to him an authority paramount above all earthly potentates. Barrow. Verses are the potent charms we use, Heroic thoughts and virtue to infuse. Waller. Exalting him not only above earthly princes and Potentates, but above the #: of the celestial hierarchy. Boyle. Oil of vitriol, though a potently acid menstruum,

will yet precipitate many bodies mineral, and others do." not only in aquafortis, but in spirit of vinegar. Id.

Each potentate, as weary fear, or strength, Or *:::: urged, his neighbour's bounds Invades. Philips.

The magistrate cannot urge obedience upon such potent grounds as the minister can urge disobedience. South. How the effluvia of a magnet can be so rare and subtile, as to pass through a plate of glass without any resistance or diminution of their force, and yet so potent as to turn a magnetick needle through the glass. - Newton's Opticks. Cyclop, since human flesh has been thy feast, Now drain this goblet potent to digest. Pope. The chemical preparations are more vigorous and potent in their effects than the galenical. Baker. With fond delight we feel the potent charm, When Zephyrs cool us, or when sun-beams warm, With fond iii. inhale the fragrant flowers, Taste the sweet fruits which bend the blushing bowers, Admire the music of the vernal grove, Or drink the raptures of delirious love. Thus did the uncircumcised potentates Of earth, debase religion in the sight Of those they ruled, who looking up beheld The fair celestial gift despised, enslaved; And mimicking the folly of the great, With prompt docility despised her too. Pollok.

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Darwin.

Fr. potenciel; Lat.

The magnifico is much beloved, And hath in his effect a voice potential, As double as the duke's. Shakspeare. Othello. This potential and imaginary materia prima cannot exist without form. Raleigh's History of the World. Manna represented to every man the taste himself did like; but it had in its own potentiality all those tastes and dispositions eminently. Taylor. The cautery is either actual or potential. - Markhan. Ice doth not only submit unto actual heat, but indureth not the potential calidity of many waters. Browne. Blackness is produced upon the blade of a knife that has cut four apples, if the juice, though both actually and potentially cold, be not quickly wiped off. Boyle on Colors. God is an eternal substance and act, without potentiality and matter, the principle of motion, the cause of nature. Stillingfleet. The true notion of a soul's eternity is this, that the future moments of its duration can never be all past and present; but still there will be futurity and

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potentiality of more for ever and ever. Bentley. This duration of human souls is only potentially

infinite. Id.

PotentIAL, in grammar, is an epithet applied to one of the moods of verbs. The potential is the same in form with the subjunctive, and is, according to Ruddiman, implied in that mood; for which reason that grammarian rejects it: but others observe that it differs from the subjunctive in this that it always carries with it the signification of power, will, or duty. It is sometimes called the permissive mood, because it often implies a permission or concession to do a thing. Por ENTIAL CAUTERY, in medicine, denotes the consuming, or reducing to an eschar, any part of the human body by a caustic alkaline or metallic salt, &c., instead of a red-hot iron, which last is called the actual cautery. POTENTILLA, silver-weed, wild tansey, or cinquefoil, a genus of the pentagynia order, and icosandria class of plants; natural order thirtyfifth, senticosae: CA. decemfid: there are five petals: seeds roundish, naked, and affixed to a small dry receptacle. The species are six: 1. P. argentea, silvery upright potentilla, has upright stalks, branching a foot high; and fivelobed leaves, having the lobes wedge-shaped, cut on the edges, hoary, and white underneath, and the branches terminated by small yellow flowers. 2. P. fragaroides, the strawberry-like potentilla, has a somewhat tuberous root, furnished with many long fibres, long trailing shoots, rooting at the joints; pinnated, mostly three-lobed leaves, having oval lobes, with the extreme lobe the largest, and clusters of small white flowers. This species bears a great resemblance to the small sterile strawberry plants. 3. P. fruticosa, the shrubby potentilla, commonly called shrub cinquefoil. This rises with a short shrubby stem, dividing into a branchy full head, three or four feet high; closely garnished with pinnated leaves of five oblong, narrow, acutepointed folioles, pale green above, and whitish underneath; and the branches terminated by clusters of large, spreading, yellow flowers. This is a beautiful deciduous flowering shrub, worthy of a place in every curious collection. It grows wild in Yorkshire, and other northern parts of England, &c., but has been long cultivated in gardens as an ornamental shrub. These plants flower in June and July; the

flowers are composed each of five roundish pe

tals, and about twenty stamina. They are all very hardy, and may be employed in the different compartments of the pleasure ground. Their propagation is very easy. The shrubby potentilla may be propagated abundantly by suckers, layers, and cuttings; all of which will readily grow, and make plants in one year, which, after having two or three years growth in the nursery, will be fit for any of the shrubbery compartments. The herbaceous kinds may be propagated by parting the roots in autumn or spring, or by seed in any of those seasons. POTERIUM, garden burnet, a genus of the polyandria order, and monoecia class of plants; natural order fifty-fourth, miscellaneae: MALE

cAL. tetraphyllous: cor. quadripartite: there are from thirty to forty stamina. FEMALE cal. tetraphyllous: cor. quadripartite: there are two pistils: the berry is formed of the indurated tube of the corolla. The species are three: 1. P. hybridum, hybrid agrimony-leaved burnet, rises with upright, taper, closely gathered stalks, two feet high; pinnated odoriferous leaves' of three or four pairs of sawed lobes, terminated

by an odd one; and the stalks terminated by

long foot-stalks, dividing into smaller, each supporting a small roundish spike of flowers. This species often proves biennial; but, by cutting down some of the stalks before they flower, it will cause it to multiply at bottom, and become abiding. 2. P. sanguisorba, the common garden burnet, has fibry perennial roots, crowned by a large tuft of pinnated leaves, or six or seven pair of sawed lobes, terminated by an odd one; upright angular stalks, dividing, and branching a foot and a half high, terminated by oblong spikes of purplish red flowers. This species grows wild in England, in chalky soils; but has been long cultivated as a choice sallad herb for winter and spring use, it being of a warm nature: the young leaves are the useful parts. It is perennial in root, and retains its radical leaves all the year; but the stalks are annual. 3. P. spinosum, shrubby spinous burnet of Crete, has a shrubby stem and branches, rising about a yard high, armed with spines; small pinnated ever-green leaves, of six or seven pairs of lobes, terminated by an odd one, and the branches terminated by small heads of greenish flowers. All these species flower in June and July, succeeded by ripe seeds in autumn. They are naturally perennial; but the two herbaceous ones are abiding in root only; the other in root, stem, and branches: the two former are hardy, and the third requires shelter in winter. The second sort merits culture in every kitchen-garden for winter and spring salads. The third sort must be kept always in pots, to have shelter in winter. They are all easily propagated, the second sort by seed and by parting the roots. The first sort may also be increased by seeds and slips off the root, as for the former sort: and the propagation of the third is by slips or cuttings of the branches in spring and summer, planted in

pots, and placed under glasses, giving shade and

water; or it might be forwarded more by plunging them in a hot-bed. Burnet is of a heating, drying nature, cordial and alexipharmic. POT'GUN, m. s. A corruption of popgun. A gun which makes a small smart noise. An author thus who pants for fame, Begins the world with fear and shame, When first in print, you see him dread Each potgun levelled at his head. Swift's Miscellanies. POTH'ECARY, n.s. A corruption of apothecary. Lat. apothecarius. One who compounds and sells physic. Modern 'pothecaries, taught the art By doctors' bills to play the doctor's part, Bold in the practice of mistaken rules, Prescribe, apply, and call their masters o: ope.

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