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, EKλEKTIKA TIç aipeois, had been introduced by Potamo of Alexandria, who selected 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. Indian pickle. A West What lord of old would bid his cook prepare Mangos, potargo, champignons, cavarre ? POTASHI, n. s. Fr. potasse. The vegetable alkali. See below. so small that no person could be remunerated by it for the trouble of the process. Messrs. Taylors 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 2d. 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 :— Saline products. Stalks of Turkey wheat, 198 lbs. or maize, Stalks of sunflower Vine branches Elm Box Sallow King. 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. În 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 afford 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 Fern cut in August 349 162.6 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 obtaining pot and pearl-ash is given by Kirwan as follows: 1. The weeds should be cut just before they seed, then spread, well dried, and 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 twelve times 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. The 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 quicklime, and, after subsidence, decanting the clear liquid, and evaporating in a loosely covered silver 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 nite, 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. 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 potential cautery for forming eschars; and it was formerly 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 thanth part of the water, at its average density. He 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 :Potassium Oxygen : . 83 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. Darracq, 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. Davy 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, aeriform 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 elec tricity 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. Curandau 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 10. 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 barns 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. The substance procured by the combustion of potassium 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. When it is heated very strongly upon platina, ter. oxygen gas is expelled from it, and there remains a difficultly 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 waWhen 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. 44 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 infiammable gas, which comes over occasionally in the production of potassium by the gun-barrel experiment. MM. Gay Lussac and Thenard describe 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 consider able 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 paper, 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 discovers 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. POTATO, in botany. See SOLANUM. 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 Linnæus, 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 when 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. POTATO. The following account of the potato was communicated to the Board of Agriculture by Dr. Wright of Edinburgh. The potato is a native of America, and was well known to the Indians long before the conquest of Mexico and Peru. Gomara, in his General History of the Indies, and Josephus Acosta, are amongst the earliest Spanish writers who have mentioned the potato by the Indian names of openanck, pape, and papas. Clusius, and after him Gerard, gave figures of the potato plant. Gerard was the first author who gave it the |