When the furnace is quite cold, the safety tube e is to be removed, and its place supplied by an iron plug. If the end of the gun-barrel, projecting from this side of the furnace, has been kept carefully cooled during the experiment, the metal will be found adhering to it, in the form of brilliant laminæ. In order to extract it, the gun-barrel is to be cut at the commencement of the part which has been kept cool, where the greatest quantity will be found. Another portion will be found close to the plug, and this adheres so slightly to the gun-barrel, that the least effort serves to detach it. It is even partly oxidized by the air, which gains access during the cooling of the furnace; and when the whole is covered with naphtha, the oxidized part is detached in laminæ, exposing a white and brilliant metallic surface. The potassium, which is condensed nearest the furnace, must be detached by a sharp chisel, and in the largest pieces we can possibly break off; for if it be in small molecules, it inflames the air, even at very low temperatures. In the middle of the gun-barrel we shall find an amalgam of potassium and iron, which becomes green on exposure to the air, the potassium returning to the state of potash. When the iron turnings were very clean, the potash very dry and pure, and the whole apparatus free from foreign matters, the metal produced differed very little from that obtained by a Voltaic battery. Its lustre, ductility, and malleability were similar. Its point of fusion and specific gravity, however, were a little higher; for it required nearly 130° Fahrenheit, to render it perfectly fluid, and was to water as 796 to 1000 at 60° Fahrenheit. This Sir H. Davy ascribes to contamination with a minute proportion of iron. The affinities, indeed, by which the decomposition is produced, he supposes to be those of iron for oxygen, of iron for potassium, and of potassium for hydrogen. Charcoal, it has been asserted by Curaudu*, may be employed, also, for the decomposition of the alkalies. To ensure success in the process, great attention, it appears, is necessary to the manipulations, which are fully described in the memoir of the inventor. The fact sufficiently explains an observation of Professor Woodhouset. A mixture of half a pound of soot and two ounces of pearlash, was exposed for two hours in a covered crucible to an intense heat. When the mixture became cold it was emptied upon a plate, and a small quantity of water poured upon it, when it immediately took fire. This could only be owing to the conversion of part of the potash into potassium. ART. 3.-Potassium. I. The base of potash, at 60° Fahrenheit, exists in small globules, which possess the metallic lustre, opacity, and general appearance of * Nicholson's Journal, xxiv. 37. VOL. I-A a † Ibid. xxi. 220. mercury; so that when a globule of mercury is placed near one of potassium, the eye can discover no difference between them. At this temperature, however, the metal is only imperfectly fluid; at 70° it becomes more fluid; and at 150° its fluidity is so perfect, that several globules may easily be made to run into one. By reducing its temperature, potassium becomes, at 50° Fahrenheit, a soft and malleable solid, which has the lustre of polished silver. At about the freezing point of water, it becomes hard and brittle, and exhibits, when broken, a crystallized texture, which, in the microscope, seems composed of beautiful facets of a perfect whiteness and high metallic splendor. To be converted into vapour, it requires a temperature approaching that of a red heat; and when the experiment is conducted under proper circumstances, it is found unaltered after distillation. II. Potassium is a perfect conductor both of electricity and of heat. III. Its specific gravity at 60° Fahrenheit, making some allowance for unavoidable errors in the experiment, is as 6 to 10, the latter number being assumed as that of water. Gay Lussac and Thenard make it between 8 and 9, and Bucholz 8.76; but they probably operated on a less pure substance. Even in its solid form, it swims in naphtha, whose specific gravity is about 7 to 10. The most recent statement of its specific gravity, by Sir H. Davy, fixes it between 8 and 9. IV. Its combustibility has already been noted. At the temperature of the atmosphere, it absorbs oxygen slowly; but if heated nearly to redness, or to its point of vaporization, it burns with a brilliant white flame and a very intense heat. V. It appears to be susceptible of different degrees or stages of oxidizement. 1stly, By heating it to a point, below what is necessary for its inflammation, either in common air or oxygen gas; or, (which is still better) by confining it, for some days, in an empty phial loosely corked, a substance is formed of a bluish grey colour, softer than wax, and readily fusible. This substance takes fire in oxygen gas, or even common air, at about 70° Fahrenheit, and acts on water, giving out hydrogen, but in less quantity than is extricated by potassium. 2. The second oxide is potash, which is most effectually produced by the action of potassium on water. 3. Potassium, gently heated on a platinum tray in oxygen gas, gives, for the result of its combustion, an orange coloured fusible substance. It is necessary to protect the platinum from its action, by dipping the tray, before the experiment, into muriate of potash melted by heat. The precise nature of this compound was first explained, and its properties examined, by Gay Lussac and Thenard. It is fusible at a lower heat than hydrate of potash, and crystallizes in laminæ by cooling. When thrown into water, oxygen gas is evolved, and the substance passes, by this loss of oxygen, to the state of potash. Oxygen gas is, also, separated, by heating it strongly on a platinum tray coated with muriate of potash; and a grey vitreous substance remains, which Sir H. Davy considers as absolutely pure potash. Almost all bodies, that have an attraction for oxygen, decompose this orange oxide, and reduce it to the state of potash, which in some cases, combines with the new compound. Charcoal, for example, with the excess of oxygen in the orange substance, forms carbonic acid; and this acid, uniting with the potash that is produced, composes carbonate of potash. VI. The action of potassium on water is attended with some beautiful phenomena. When it is thrown upon water exposed to the atmosphere, or when it is brought into contact with a drop of water, it decomposes the water with great violence; an instantaneous explosion is produced with a vehement flame; and a solution of pure potash is the result. The hydrogen gas, which is disengaged, appears to dissolve a portion of potassium; for, on escaping into the air, it forms a white ring of smoke, gradually enlarging as it ascends, like the phosphureted hydrogen gas. When water is made to act on the base of potash, atmospheric air being excluded, there is much heat and noise, but no luminous appearance; and the gas evolved is pure hydrogen. It is of importance to remember that each grain of potassium, by acting on water, detaches about 1.06 cubic inch of hydrogen gas. If a globule of the base of potash be placed on ice, it instantly burns with a bright flame, and a deep hole is made in the, ice filled with a fluid which is found to be a solution of potash. The production of alkali, by the action of water on potassium, is most satisfactorily shown, by dropping a globule of the metal upon moistened paper, which has been tinged with turmeric. At the moment when the globule comes into contact with the paper, it burns, and moves rapidly as if in search of moisture, leaving behind it a deep reddish brown trace, and acting upon the paper exactly like dry caustic potash. So strong indeed is the affinity of potassium for oxygen, that it discovers and decomposes the small quantities of water contained in alcohol and ether, even when carefully purified, and disengages, from both these fluids, hydrogen gas. On naphtha colourless and recently distilled, potassium has very little power of action; but in naphtha, which has been exposed to the air, it soon oxidates, and alkali is formed, which unites with the naphtha into a brown soap, that collects round the globules. VII. When thrown into the liquid mineral acid, the base of potash inflames, and burns on the surface; or, if kept beneath the surface, its effects are such as may be explained by its affinity for oxygen. In concentrated sulphuric acid, a white saline substance is formed, which is probably concentrated sulphuric acid surrounded by sulphur. At the same time a gas escapes which has the smell of sulphurous acid mixed with hydrogen gas. In nitrous acid, nitrous gas is disengaged, and nitre of potash is formed. In oxymuriatic acid gas, it burns vividly with bright scintillations, and muriate of potash is generated. VIII. Potassium readily combines with the simple combustibles. To unite it with sulphur or phosphorus, it must be melted with these bodies under naphtha. The phosphuret of potassium requires for its fusion a stronger heat than either of its constituents. It is of the colour of lead; and, when spread out, has a lustre similar to polished lead. By exposure to the air, or by rapid combustion, forms phosphate of potash. Besides this, there is, also, a chocolate coloured compound of potassium and phosphorus; so that it is probable these two bodies unite in different proportions, the lead coloured compound consisting of 2 atoms of metal +1 of phosphorus; and the chocolate of 1 atom of metal + 1 of phosphorus. When potassium is fused with sulphur, in a vessel filled with the vapour of naphtha, a rapid combination ensues, accompanied with heat and light, and a disengagement of sulphureted hydrogen. The result is a grey substance not unlike artificial sulphuret of iron. Its formation and properties have been investigated by Vauquelin*. IX. With mercury, potassium gives some extraordinary and beautiful results. The combination is very rapid, and is effected by merely bringing them into contact at the temperature of the atmosphere. The amalgam, in which the potassium is in least proportion, seems to consist of about 1 part in weight of basis and 70 of mercury. It is very soft and malleable; but by increasing the proportion of potassium, we augment, in a proportional degree, the solidity and brit tleness of the compound. The compound of mercury and potassium may be obtained by an easy and simple process, first pointed out by Berzelius. Mercury, to the depth of a line, is put into a glass capsule, two inches in diameter, with a flat bottom. On this a solution of pure potash is poured; an iron wire connects the mercury with the negative pole of a galvanic arrangement, which needs not contain more than 20 pairs of plates; and a spiral platina wire, from the positive pole, is immersed in the solution, and kept within about a line from the surface of the mercury. In six hours, the effect is observable, and in 24 very distinct: for in that time, more than 1200 grains of mercury will be rendered solid by combination with potassium. Unfortunately, this combination cannot be so decomposed, as to obtain the potassium in a separate state. is In this state of division, potassium appears to have its affinity for oxygen considerably increased. By a few minutes exposure to the air, potash is formed which deliquiates, and the mercury is left pure and unaltered. When a globule is thrown into water, it produces a rapid decomposition and a hissing noise; potash is formed; pure hydrogen disengaged; and the mercury remains free. The fluid amalgam of potassium and mercury dissolves all the metals; and in this state of union, mercury even requires the power of acting on platina. Potassium unites, also, with gold, silver, and copper; and, whe the compounds are thrown into water, this fluid is decompose potash is formed, and the metals are separated unaltered. When the reduction of an ore has been accomplished by the use of fluxes containing potash, M. Vauquelin has shown that the revived metal contains a greater or less proportion of potash, which modifies its properties. By exposure to the air, or by the action of water, this impurity may be removed*. poses X. Potassium reduces all the metallic oxides when heated with them, even of those metals which most powerfully attract oxygen, such as oxides of iron. In consequence of this property it decomand corrodes flint and green glass by a very gentle heat; potash is generated with the oxygen taken from the metal, which dissolves the glass and exposes a new surface. At a red heat even the purest glass, formed merely of potash and silex, is acted upon. The alkali in the glass seems to give up a part of its oxygen to the potassium, and an oxide of potassium results, with a less proportion of oxygen than is necessary to constitute potash. The sílex, also, it is probable, is partly de-oxidized. From this summary of the action of potassium, it appears that all the most remarkable effects which it exhibits, are connected with its affinity for oxygen, which is sufficiently energetic to enable it to take oxygen from all other bodies. Hence the application of potassium to any substance is the best test of its containing oxygen, which, if present, it cannot fail to detect. It was important to determine the proportions in which potassium and oxygen combine, when potash is regenerated. This Sir H. Davy investigated by two different processes. The one consisted in ascertaining how much oxygen gas disappears by the action of a given quantity of potassium; the other how much hydrogen is disengaged from water by a known weight of the same substance. Dividing the bulk of the hydrogen gas by 2, he learned the quantity of oxygen which had been taken from the water. The coincidence of results, obtained by these different methods, is remarkable. By the action of potassium on oxygen gas, it ap peared, on an average, that 86.1 potassium, 13.9 oxygen. 100. By the agency of water, the proportions differed only by a small fraction, so that we may state in round numbers that the base is to oxygen as six to one, or that the Potash is composed of { 86 potassium, 100. Subsequent experiments, however, have made some change neces sary in these numbers. Gay Lussac and Thenard found, that 100 parts by weight of potassium take 19.945 of oxygen from water; and * Ann. de Chim. et Phys. vii. 32. |