Potassium permanganate

“ The usual laboratory solution of potassium permanganate must be frequently restandardized. A slight loss in strength may be detected after standing even a few days and this change becomes more rapid as the decomposition proceeds. When one looks for the cause of this increase in the rate of the decomposition of the permanganate, the attention is naturally directed to the brown manganese oxide which [Pg 2] separates from the solution. A desire to ascertain whether the presence of this oxide influences the rate of the decomposition suggested the experiments here described. ”

“ The conclusions to be drawn from the foregoing results are (1) that dilute solutions of potassium permanganate are more stable both in diffused light and in darkness than the more concentrated ones, and (2) that the presence of manganese oxides hasten to an enormous degree the reduction of potassium permanganate even at summer temperatures. It will also be observed that this reducing action of the manganese oxide is greater in the stronger than in the more dilute solutions. It should be remarked that the summer of 1892 in which these experiments were made, was one of unusual heat. ”

“ The solution of permanganic acid forms a bright red liquid which reflects a dark violet tint. A dilute solution has exactly the same colour as that of the potassium salt. It deposits manganese dioxide when exposed to the action of light, and also when heated above 60°, and this proceeds the more rapidly the more dilute the solution. It shows its oxidising properties in many cases, as already mentioned. Even hydrogen gas is absorbed by a solution of permanganic acid; and charcoal and sulphur are also oxidised by it, as they are by potassium permanganate. ”

“ Commercial potassium permanganate is rarely sufficiently pure to admit of its direct weighing as a standard. On this account, and because of the uncertainties as to the permanence of its solutions, it is advisable to standardize them against substances of known value. Those in most common use are iron wire, ferrous ammonium sulphate, sodium oxalate, oxalic acid, and some other derivatives of oxalic acid. With the exception of sodium oxalate, these all contain water of crystallization which may be lost on standing. They should, therefore, be freshly prepared, and with great care. ”

“ The first two results are from experiments in which the action was stopped at the first loss of the color of potassium permanganate. The last two are the results from experiments in which the action was stopped after the oxide had settled leaving a clear colorless supernatant liquid. The amount of oxygen given off in any one case is expressed in the table as the number of atoms of oxygen derived from each molecule of potassium permanganate, as follows: [Pg 29]
The volume of the oxygen evolved is considerably smaller than that obtained when the brown oxide was used. ”

“ Animal charcoal of itself will often decolourise potassium permanganate. If this correspondent wishes to test her filter more thoroughly, let her take out the carbon block and place it in a clean jug full of water, to which one or two drops of the permanganate solution has been added so as to make it a very, very pale pink. Having left it an hour or so, let her place a sheet of white paper behind the jug and see if the solution round the carbon block is paler in tint than the rest of the fluid. Even if this test is negative it will not prove that the carbon block is free from germs ”

“ Potassium permanganate, in the presence of dilute sulphuric acid, is rapidly reduced by hydrogen peroxide, oxygen being given off, 2KMnO4 + 3H2SO4 + 5H2O2 = K2SO4 + 2MnSO4 + 8H2O + 5O2. Lead peroxide is reduced to the monoxide. ”

“ Obtained by distilling cautiously potassium permanganate and sulphuric acid. Dark violet-black liquid, green by reflected light, and rapidly absorbing water forming a violet solution. Oxidises organic matter with explosive violence.
Permanganate of Barium. Ba (MnO) 45. Black soluble prisms, formed by decomposing silver permanganate by means of barium chloride, and cautiously evaporating.
Permanganate of Potassium. KMnO4. Prep. Potassium chlorate, or nitrate, and potassium hydrate are made into a paste with water, and manganic peroxide added; the mass is dried and heated to redness. ”

“ Then four to six ounces of the pharmacopœial solution of potassium permanganate, or twenty to thirty grains of the solid permanganate in a quart of distilled water, and ten drops of strong sulphuric acid, should be poured through, and subsequently a quarter to half an ounce of pure hydrochloric acid in two to four gallons of distilled water. This plan would be useful on foreign stations where the filter cannot be sent home, or taken to pieces; if it can be taken to pieces, the charcoal should be spread out in a thin layer, and exposed for some time to air or sun, or heated in an oven. ”

“ Acid neutralized = 38.10 percent.
XI. The flask contained black oxide 150 m.g. potassium permanganate 20 c.c. = 177.71 m.g., N/10 nitric acid 22.39 c.c. (= 2 molecules for each molecule of KMnO4) and was heated four and one half hours in the water bath.
Acid neutralized = 100.00 percent.
No definite conclusions can be drawn from these neutralization experiments since it is well known that manganese oxides prepared as were those used in these experiments always contain some, though probably not a constant quantity of alkali. ”

“ It is easily soluble in water and alcohol, and is thrown out of its aqueous solution by the addition of calcium chloride. Potassium bichromate and sulphuric acid oxidize it to carbon dioxide and acetic acid, while alkaline potassium permanganate oxidizes it to carbon dioxide. ”

“ The possibility of a reaction analogous to that between potassium permanganate and lead dioxide in the presence of strong nitric acid seems to be excluded by the fact that the higher oxides of manganese may be prepared in the presence of concentrated nitric acid. ”

“ Potassium permanganate hair dye.—Potassium permanganate 5 ozs., distilled water 2 quarts. Crystallized potassium permanganate dissolves with great ease in water to a deep violet fluid. By bringing the solution in contact with an organic substance—paper, linen, skin, horn, hair—it rapidly discolors, imparting to the substances a brown color, which originates from peroxide of manganese. Free the hair from fat by washing, and apply the dilute solution with a soft brush. ”

“ It has already been noted that hydrochloric acid reacts slowly in cold solutions with potassium permanganate. It is, however, possible to obtain a satisfactory, although somewhat fugitive end-point in the presence of manganous sulphate and phosphoric acid. The explanation of the part played by these reagents is somewhat obscure as yet. It is possible that an intermediate manganic compound is formed which reacts rapidly with the ferrous compounds—thus in effect catalyzing the oxidizing process. ”

“ Manganese heptoxide, Mn2O7, prepared by adding pure potassium permanganate to well cooled, concentrated sulphuric acid, when the oxide separates as a dark oil (H. Aschoff, Pogg. Ann., 1860, 111, p. 217) , is very unstable, continually giving off oxygen. It decomposes violently on heating, and explodes in contact with hydrogen, sulphur, phosphorus, &c. It dissolves in water to form a deep red solution which contains permanganic acid, HMnO4. This acid is also formed by decomposing barium or lead permanganate with dilute sulphuric acid. It is only known in aqueous solution. ”

“ It is generally known as the “Forchammer” or “oxygen” process, and, although of undoubted service in comparing the quality of samples of very impure water, it is defective in the following important respects: Different organic substances are not affected to an equal extent by potassium permanganate; albumen, for instance, being far less easily oxidised than other compounds, and the value of the results afforded is vitiated by the presence of certain inorganic bodies, such as nitrites, sulphuretted hydrogen, ferrous salts, etc. ”

“ If we bring permanganate, against potassium iodide, into the beakers of the chemometer (p. 253) , we find that it is a much more vigorous oxidizing agent than is arsenic acid, and again we find that the addition of acid (sulphuric) to the permanganate solution enormously increases the potential (exp.) and therefore its oxidizing power. The addition of an acid would, obviously, enormously increase the concentration of a positive septavalent ion, if permanganic acid is assumed to be, to a slight extent, base forming and therefore amphoteric ”

“ They are isomeric with the cinnolines, phthalazines and quinoxalines. They may be obtained by the action of alcoholic ammonia on the acidyl derivatives of orthoaminobenzaldehydes and ortho-aminoketones (A. Bischler, Ber., 1891–95) :
and from the corresponding dihydro compounds on oxidation with potassium permanganate. They are stable, tertiary bases, and may be distilled without decomposition; they form addition products with alkyl iodides and double salts with mercuric and platinum chlorides. On reduction with sodium in presence of alcohol they yield dihydro derivatives. ”

“ Calcium Permanganate Merck.—C.P., Cryst.
Deliquescent, brown cryst.—Sol. in water.—Uses: Intern., gastro-enteritis and diarrhea of children; extern., as other permanganates for mouth lotions and for sterilizing water; and vastly more powerful than potassium permanganate.—Dose: 3/4—2 grn., well diluted.
Calcium Phosphate, Tribasic, Merck— (Precipitated Calcium Phosphate, U.S.P.) .—Pure, Dry.
Dose: 10—20 grn.
Calcium Sulphite Merck.—Pure.
White powd.—Sol. in 20 parts glycerin, 800 parts water.—Antizymotic.—Uses: Flatulence, diarrhea, and some dyspepsias.—Dose: 2—5 grn., in pastilles. ”

“ In a solid state it is decomposed by heat, with evolution of [312] oxygen, a residue consisting of the lower oxides of manganese and potassium oxide being left. [22 bis] A mixture of permanganate of potassium, phosphorous and sulphur takes fire when struck or rubbed, a mixture of the permanganate with carbon only takes fire when heated, not when struck. The instability of the salt is also seen in the fact that its solution is decomposed by peroxide of hydrogen, which at the same time it decomposes. ”

“ Dry the filter, transfer the cleaned ore to a piece of combustion tube ten or twelve inches long and narrowed at one end. Pass a current of hydrogen through the tube and heat to redness for 30 minutes; cool whilst the gas is still passing. Dissolve in 20 c.c. of dilute hydrochloric acid and keep the solution tinted with permanganate of potassium. When the colour of the permanganate becomes permanent dilute to a bulk of 50 c.c. with water, filter, and wash. Heat; add a rod of zinc weighing about 3 grams ”

“ It is susceptible of wider application by mixing reducing agents with the soda-lime: thus Goldberg (Ber. 16, p. 2546) uses a mixture of soda-lime, stannous chloride and sulphur for nitro- and azo-compounds, and C. Arnold (Ber. 18, p. 806) a mixture containing sodium hyposulphite and sodium formate for nitrates.
Kjeldahl’s Method.—This method rapidly came into favour on account of its simplicity, both of operation and apparatus. Various substances other than potassium permanganate have been suggested for facilitating the operation ”

“ Rapid cooling is followed by the formation of small columnar crystals; slow cooling gives large prismatic crystals. The composition of the salt is determined either by igniting it, when it forms sulphate of potassium, or else by titrating the active oxygen with permanganate: its composition was found to correspond to the salt of persulphuric acid, K2S2O8. The solution of the salt has a neutral reaction, and does not give a precipitate with salts of other metals. K2S2O8 is the most insoluble of the salts of persulphuric acid. ”