Potassium alum

“ Those elements which unite with the utmost eagerness at ordinary temperatures, seem to become indifferent 272to each other when subjected to the extremes of heat and cold. Potassium unites fiercely with oxygen in the most familiar of all chemical experiments. Potassium is indeed a strange metal, for it is of such small density that a piece cast on a basin of water will float like a chip of wood. It has such avidity for oxygen that it will decompose the water to wrench the molecules of oxygen from those of hydrogen. ”

“ The paper will be found covered with a solution of ordinary potash. If turmeric paper be used, the course of the potassium will be marked with a deep brown color.—Corollary. Hence, if you touch potassium with wet fingers you will burn them.
If a small piece of the metal be placed on a piece of ice, it will instantly take fire, and form a deep hole, which will be found to contain a solution of potash.
In consequence of its great affinity for oxygen, potassium must be kept in some fluid destitute of that element, such as naphtha. ”

“ This shows that the molecule of potassium (like that of sodium, mercury, and zinc) contains but one atom. This is also the case with many other metals, judging by recent researches. [19] The specific gravity of potassium at 15° is 0·87, and is therefore less than that of sodium, as is also the case with all its compounds. [20] Potassium decomposes water with great ease at the ordinary temperature, evolving 45,000 heat units per atomic weight in grams. The heat evolved is sufficient to inflame the hydrogen, the flame being coloured violet from the presence of particles of potassium. ”

“ At 32° F. it is brittle, like glass; at 59° it is soft and malleable; at 144° it becomes liquid. Potassium is widely diffused in the vegetable, animal and mineral kingdoms. Some of the more important potassium compounds are caustic potash (the hydroxide) , the carbonate, the bicarbonate; also potassium chloride, bromide, iodide, nitrate (saltpeter) , sulphate, chlorate, cyanide etc. Of these iodide, bromide and chlorate are used for medicines, the others being employed more or less in the arts. ”

“ The term potash is commonly used to designate any of the salts of the element potassium, particularly those soluble in water, which are largely used in agriculture and manufacturing. The element potassium is widely distributed as a component of rocks, soils, and vegetable and animal substances, but large quantities of potassium salts in forms suitable for the uses of man have been found in only a few places. Ashes of wood, which were formerly the principal source of potash in commerce, now supply an inconsiderable part of the world’s requirements. ”

“ The discovery of potassium led to that of the true nature of what had been long familiar to chemists by the name of pure Potash, but which ought to 284 have been called the hydrat, for the pure alkali was not known until after the discovery of Davy. The experiments of MM. Gay Lussac and Thénard have shown this substance to be a Protoxide. It is difficult of fusion; it has a grey colour and a vitreous fracture, and dissolves in water with much heat. The Peroxide is procured by the combustion of potassium at a low temperature ”

“ Hard soap is a combination of oil or fat, and soda. The quantity of real alkali in potash may be known by the proportion of acid required to saturate a given weight of it. Potash, pearl-ash, salt of tartar, and salt of wormwood are all carbonates of potassa. This alkali is called the vegetable alkali, because it is obtained from vegetables. It is considered to be the hydrated deutoxide of potassium, and when decomposed will furnish potassium.
Table of the saline or soluble products of one thousand pounds of ashes of the following vegetables. ”

“ It is apparent that metallic salts of organic acids would, in aqueous solution, be ionized, the positive ion being the metal, and the negative ion the acid residue. Esters, however, are not ionized. It is therefore apparent that a mixed salt and ester, for example KO2C·CH2·CH2·CO2C2H5, would give only two ions, viz. potassium and the rest of the molecule. If a solution of potassium acetate be electrolysed the products are ethane, carbon dioxide, potash and hydrogen; in a similar manner, normal potassium succinate gives ethylene, carbon dioxide, potash and hydrogen ”

“ It ignites instantly when brought in contact with water. Within that little globule of potassium, I have imbedded a pill of my own composition and discovery. The moment it is liberated from the potassium, it commences the work of decomposing the fluid on which it floats. The potassium at once ignites the liberated oxygen, and the conflagration of this mighty globe is begun. ”

“ The molecule of metallic potassium (Scott, 1887) , like that of mercury, contains only one atom, and it is probably in virtue of this that the molecules CO and K combine together. But as in the majority of cases potassium acts as a univalent radicle, the polymeride K2C2O2 is formed, and probably K10C10O10, because products containing C10 are formed by the action of hydrochloric acid. The black mass formed by the combination of carbonic oxide with potassium explodes with great ease, and oxidises in the air. ”

“ Here is a little piece of the metal potassium, one of the simple substances of the earth; that is to say, we cannot split it up into other substances, wherever we find it, it is always the same. Now if I put this piece of potassium on the water it does not disappear quietly like the sugar. See how it rolls round and round, fizzing violently with a blue flame burning round it, and at last goes off with a pop. ”

“ Our pint of water would then occupy 1800 times its present volume.
Let us now give a striking and beautiful illustration of chemical affinity. We will throw into this tumbler a piece of potassium (symbol K) half as large as a pea. This interesting metal was discovered by Davy in 1807. Its affinity for O is very great. As soon as it falls upon the water it abstracts oxygen and forms potassium oxide (potash) , while the hydrogen and a small amount of volatilized K escape and are burned with a brilliant violet flame, on account of the heat evolved by the energetic chemical action. ”

“ It must be observed that potassium decomposes carbonic anhydride and carbonic oxide when heated, the carbon being liberated and the oxygen taken up by the metal, whilst on the other hand charcoal takes up oxygen from potassium, as is seen from the preparation of potassium by heating potash with charcoal, hence the reaction K2O + C = K2 + CO is reversible and the relation is the same in this case as between hydrogen and zinc. ”

“ POTASH, SODA, and AMMONIA. The two first are called fixed alkalies, because they exist in a solid form at the temperature of the atmosphere, and require a great heat to be volatilised. They consist, as you already know, of metallic bases combined with oxygen. In potash, the proportions are about eighty-six parts of potassium to fourteen of oxygen; and in soda, seventy-seven parts of sodium to twenty-three of oxygen. The third alkali, ammonia, has been distinguished by the name of volatile alkali, because its natural form is that of gas. ”

“ Potassium is one of the eight most abundant elements in the earth. It occurs as a primary constituent of most igneous rocks, [Pg 113] some of which carry percentages as high as those in commercial potash salts used for fertilizers. It is present in some sediments and likewise occurs in many schists and gneisses. Various potassium silicates—leucite, feldspar, sericite, and glauconite—and the potassium sulphate, alunite, have received attention and certain of them have been utilized to a small extent, but none of them are normally able to compete on the market. ”

“ Carbonic ether, Carbonate of oxide of ethyl; Æther carbonicus, L. Prep. Fragments of potassium are added to oxalic ether, gently warmed, as long as bubbles of gas are formed; the excess of metal is removed from the semi-solid mass, some water added, and the whole distilled. The carbonic ether floats on the surface of the liquid in the receiver, and is collected, dried by contact with chloride of calcium, and rectified along with some potassium or sodium, till it ceases to yield acetate of potassa when acted on by caustic potassa. ”

“ They boldly assume that the discrepancies are due to experimental errors, and they are justified by the fact that the more elaborate and skilful the researches on the subject, the more nearly their assumption is verified. Potassium is the only element whose atomic weight has been determined with great care, but which has not shown an approach to a simple ratio with the other elements. ”

“ We are not authorized to infer the pre-existence of ammonium, however, from the [Pg 35] appearance of this reaction, for the presence of nitrogenous organic matter in the substance, which would be decomposed by this treatment, would give rise to such a reaction.
18. Potassium.—Potassium is recognized by the color which its salts impart to the Bunsen flame. If a portion of a salt of potassium be held on a platinum wire in the flame, it imparts a blue-violet tint which rapidly disappears.
19. Sodium.—Like potassium, this alkali metal is detected by the color which its salts give to the flame. ”

“ Potassium has a bright, almost silvery, appearance, and is so greatly attracted by oxygen that it cannot be kept anywhere if that element be present—not even in water, for combustion will immediately ensue on water ”

“ That cannot, however, be precisely the reason, for when potassium is introduced under water, without contact of air, the combustion is not so rapid, and indeed, in that case, there is no luminous appearance; but a violent action takes place, much heat is excited, the potash is regenerated, and hydrogen gas is evolved.
Potassium is so eminently combustible, that instead of requiring, like other metals, an elevation of temperature, it will burn rapidly in contact with water, even below the freezing point. ”

“ A very good test is the process of reduction with potass, by which globules of mercury are sublimed, and a chloride of potassium left in the flux, as may be proved by the action of nitrate of silver on the solution of the flux previously neutralized with nitric acid. ”

“ His object was twofold: to refute the hypothesis which assumed hydrogen as an element of potassium, and to ascertain the nature of the matter existing in the amalgam of ammonia, or the supposed metallic basis of the volatile alkali: a question intimately connected with the whole of the arrangements of chemistry. As to the former point, it is unnecessary to enter into farther discussion; and with regard to the latter, it is quite impossible to convey an adequate idea of the extent of the enquiry: there does not exist in the annals of chemistry a more striking example of experimental industry. ”

“ Potassium, the metallic basis of potash, was discovered by Sir Humphrey Davy in 1807, who succeeded in separating it from potash by means of a powerful voltaic battery. Its great affinity for oxygen causes it to decompose water with evolution of hydrogen, which takes fire with the heat produced. ”

“ The potassium salt is formed by the action of potassium ethylate on tetranitromethane (A. Hantzsch, Ber., 1899, 32, p. 631) . It is a deep yellow coloured solid, which is readily soluble in water. It explodes when heated. ”

“ Sulphide of ammonium gives similar reaction. Ammonia and potassa produce bulky reddish-brown precipitates insoluble in excess. Ferrocyanide of potassium gives a rich blue precipitate, insoluble in hydrochloric acid, and readily decomposed by potassa. Ferricyanide of potassium deepens the colour, but does not give a blue precipitate, as it does with ferrous salts (proto salts) . Sulphocyanide of potassium gives an intense ruby-red colour to neutral or acid solutions. Tincture and infusion of galls strike a black colour. ”

“ The animal body also contains potassium compounds, which is natural, since animals consume plants. For example, milk, and especially human milk, contains a somewhat considerable quantity of potassium compounds. Cow's milk, however, does not contain much potassium salt. Sodium compounds generally predominate in the bodies of animals. The excrement of animals, and especially of herbivorous animals, on the contrary, often contains a large proportion of potassium salts. Thus sheep's dung is rich in them, and in washing sheep's wool salts of potassium pass into the water. ”

“ Not an atom of potassium can be obtained unless the potassa be moistened; nor can any salt be decomposed except water be present. Sir Humphry says, it is required, to render the substance a conductor; but its operation is more recondite, and there is something mysterious and still unexplained in the uniform appearance of hydrogen and oxygen at the opposite poles, when far apart in water, and in all other cases of true polar electro-chemical decomposition. ”

“ The oxidation of the potassium salt is effected as follows. 50 grams of the salt are dissolved in 21⁄2 litres of water, and to this is added a solution of 15 grams of potassium hydroxide. The mixture is heated to 100° on a water-bath, and when this temperature is reached, 110 grams of potassium permanganate are added. Heating is continued until the solution is decolorized, care being taken to prevent the evolution of free oxygen. ”

“ It forms a grey brittle mass, having a conchoidal fracture; it is Very deliquescent, combining very energetically with water to form caustic potash. According to Holt and Sims (Journ. Chem. Soc., 1894, p. 438) , the substance as obtained above always contains free potassium. Potassium hydroxide or caustic potash, KOH, formerly considered to be an oxide but shown subsequently to be a hydroxide of potassium, may be obtained by dissolving the metal or monoxide in water, but is manufactured by double decomposition from potassium carbonate and slaked lime: K2CO3+Ca (OH) 2=2KOH+CaCO3. ”