Principles of Pharmacy

Colorless, transparent, six-sided, rhombic prisms, or a white crystalline powder; odorless and having a cooling, saline, and pungent taste. Slightly hygroscopic in moist air.

Soluble in 3.6 parts of water at 25° C. (77° F.) and in 0.4 part of boiling water; very sparingly soluble in alcohol.

When heated to 353° C. (667.4° F.) the salt melts. At a higher temperature it is decomposed, giving off oxygen at first, and then some of its nitrogen, leaving a residue of potassium nitrate, nitrite, and oxide. When thrown upon red-hot coals the salt deflagrates.

The aqueous solution is neutral to litmus-paper.

Tests for Identity.-See Potassium and Nitrates in Part V.

Impurities. Heavy metals, iodide, chlorate, and perchlorate. Details in Plate V.

Remarks. This chemical, commonly called saltpetre, has been in popular use for centuries. The original method of manufacture was interesting; being made by the treatment of ashes with decaying nitrogenous matter, such as manure and cattle urine. The mass was allowed to stand under roughly constructed sheds for several months, being occasionally turned so as to present new surfaces to the air. When the fermentation of the mass is completed, it is placed in crude percolators and lixiviated with water, whereby the finished potassium nitrate is separated from the extraneous matter. Repeated crystallization of this solution eventually results in a pure crystalline nitrate.

Investigations of the manufacture of saltpeter on these "saltpetre plantations" has shown that the change of the nitrogenous matter to the nitrate is a species of fermentation, being produced by a peculiar microscopic plant called nitromonas. This process of saltpetre manufacture was formerly largely used, as it yielded not only all the saltpetre used, but also because this potassium nitrate was the source of nitric acid and all the nitrates.

At present, however, the source of nitric acid is Chile salt petre (see p. 468), from which potassium nitrate is made, as shown in the following equation:

the resulting salts being separated by fractional crystallization. One of the largest general uses of potassium nitrate is in the manufacture of gunpowder, of which the average formula is potassium nitrate, 75 parts; powdered charcoal, 15 parts; and sulphur, 10 parts. the mass being mixed together, then granulated by wetting the mass, passing it through a sieve, and carefully drying the resulting granules. Gunpowder explodes by the following reaction:

2KNO, S + 3C

K2S+ 3C0, + N2.

On examination of the above equation it will be seen that the chemical action between the three solids results in the formation of two gases and a comparatively small amount of the solid potassium sulphide. One volume of gunpowder gives 280 volumes of mixed gases, and on this property hinges the whole theory of explosion, which means the sudden evolution of a large volume of gas from a comparatively small quantity of the solid or liquid.

In the potassium sulphide of the above reaction is found an explanation of the peculiar odor of a burned fire-cracker.

In medicine, potassium nitrate is used largely as a diuretic.
Dose.-500 milligrammes (7) grains).

Potassium nitrate acts as an oxidizing agent in the explosion of gunpowder, and to this oxidizing action is due the value of potassium nitrate as an antiseptic. Its use as a preservative of meat and other foods is too well known to require extended comment here.

POTASSII PERMANGANAS.

KMnO1

Potassium Permanganate.

156.98

It should contain not less than 99 per cent. of pure Potassium Permanganate [MnO,.OK] and should be kept in glass-stoppered bottles, protected from light. Potassium Permanganate, when in concentrated solution or in the dry condition, should not be brought in contact with organic or other readily oxidizable substances.

Slender, monoclinic prisms, of a dark purple color, almost opaque by transmitted light, and of a blue, metallic lustre by reflected light, odorless, and having a taste at first sweet, but afterward disagreeable and astringent.

the air.

Permanent in

Soluble in about 15 parts of water at 25° C. (77° F.) and in 3 parts of boiling water; in contact with alcohol it is decomposed.

When heated the salt decrepitates, and at 240° C. (464° F.) it decomposes, yielding oxygen, potassium manganate, and manganese dioxide.

The aqueous solution of the salt is of a deep violet-red color when concentrated and of a rose color when much diluted, and the rose color is discharged by hydrogen sulphide, ferrous sulphate, oxalic acid, alcohol, hydrogen dioxide, and many other readily oxidizable substances, especially if the solution be first rendered acid by sulphuric acid,

An aqueous solution is neutral to litmus-paper.

Tests for Identity.-See Potassium and Permanganates in Part V. Impurities. Excess of sulphates, chlorides, nitrates. Part V.

Assay.-Details in Part V.

Details in

Remarks.-Potassium permanganate is now given the formula KMnO1, in preference to that of the pharmacopoeia of 1880, K2Mn2O. It represents the highest known valence of manganese,-the valence VII, and is an analogue of potassium perchlorate, KCIO,, which comes from perchloric oxide, Cl2O,, the graphic formula of which was given on p. 365. The permanganate is one of the oxidizing agents, the action of which is explained on p. 425.

It is made by treatment of manganese dioxide with potassium hydroxide and potassium chlorate, this mixture yielding potassium manganate, as shown in the following equation:

3MnO,

6KOH +

+ KCIO,

3K,MnO + KCI +

3H2O. It will be observed that potassium manganate (K,MnO) has a formula similar to that of potassium sulphate, in this body the manganese acting with the valence vi. When this green potassium manganate is boiled with water, it is converted into the purple potassium permanganate, as shown in the following equation:

3K,MnO

3H,0 +

2KMnO, + MnO2 + 4KOH + H2O.

The process occurs in miniature in an important test for manganese, which consists of fusing the three constituents above given on

a piece of platinum foil and then boiling in water.

If the fused mass is green and the resulting liquid is pink, it indicates the presence of manganese.

By reason of this change of tint, potassium permanganate has been given the synonym of mineral chameleon.

It will be noticed that the products of the final reaction consist of some binoxide of manganese and also potassium hydroxide, and in order to secure the permanganate from this mixture, it is necessary to neutralize the excess of potassium hydroxide with sulphuric acid. The solution of permanganate is then filtered through asbestos to remove the precipitated manganese dioxide, and the filtrate concentrated until crystallization begins.

Potassium permanganate occurs in purple, monoclinic crystals, which possess a blue, metallic luster in reflected light. It is soluble in 16 parts of water and forms a purple-red solution. The pharmacopoeia gives a warning that it should never be triturated with easily oxidizable substances, while pills of potassium permanganate should not be made with ordinary excipients, but with petroleum mass (petrolatum and kaolin).

The oxidizing action of potassium permanganate in neutral solution is best shown by the following equation: 0.

2KMnO, + H2O

2MnO, + 2KOH +

This, when reduced into words, means that two molecules of the permanganate yield three molecules of available oxygen. By comparison of this with the oxidizing equation of nitric acid, given on p. 420, it is seen that the process of the two cases is similar.

When permanganate acts in acid solution, two molecules (or one molecule of K.Mn,O, if that is accepted as the formula) liberate five atoms of oxygen, as shown in the following equation:

2KMnO1 + 3H2SO 2MnSO, + K2SO、 + 3H2O + 0 ̧. This is the basis of the use of potassium permanganate in volumetric analysis (p. 1006).

Potassium permanganate is one of the most convenient oxidizing agents for use in organic chemistry. As already stated, nitric acid is the oxidizing agent generally used in the ordinary processes of oxidation we meet in pharmacy. The acid, however, acts too violently for use in many organic oxidations, and for such purposes either potassium permanganate or chromic acid is employed. The only pharmaceutic application of this use of permanganate is in purifying alcoholic distillates. In such cases it is well to note that the permanganate decomposes with the formation of not only insoluble manganese dioxide, but also potassium hydroxide, which will go into solution. Therefore, before such purified alcohol can be employed, it should be redistilled.

Potassium permanganate is a valuable antiseptic in medicine, and is largely used in surgical practice. One advantage it possesses over the ordinary oxidizing antiseptics is its comparative freedom from caustic action. In practice it is frequently prescribed in the form of Condy's fluid, which consists of 128 grains permanganate to one pint of distilled water.

Dose.-65 milligrammes (1 grain), preferably in a fine powder in capsules.

It should contain not less than 99 per cent. of pure Potassium Sulphate [SO2(OK),].

Hard, colorless, transparent, six-sided, rhombic prisms terminated by pyramids, or a white powder, odorless, and having a somewhat bitter, saline taste. Permanent in the air.

Soluble in about 9 parts of water at 25° C. (77° F.) and in 4 parts of boiling water; insoluble in alcohol.

When heated the crystals decrepitate. At a bright red heat they fuse, and at a white heat the salt suffers partial decomposition.

The aqueous solution is neutral to litmus-paper.

Tests for Identity.-See Potassium and Sulphates in Part V.
Impurities.-Heavy metals and arsenic. Details in Part V.

Remarks. This body occurs in nature in the ore, kainite, of the composition K2SO,MgSO,MgCl25H2O. It is made artificially by treating either potassium nitrate or potassium chloride with sulphuric acid. It is in the form of colorless, transparent, rhombic crystals, soluble in 9 parts of water. It is interesting to note that these crystals contain no water of crystallization, thereby differing from the otherwise similar sodium sulphate, which contains ten molecules of water of crystallization.

Potassium sulphate is employed as a diuretic and refrigerant. Its use is rather limited, especially as the pharmacopoeia has omitted its use in the manufacture of Dover's powder, the original recipe for this pharmaceutic directing that the ipecac and opium be triturated with crystallized potassium sulphate; but in the present pharmacopoeia sugar of milk is substituted for this salt. (See p. 304.) Dose.-2 Gm. (30 grains).

CHAPTER XXVI

SODIUM.

Symbol, Na. Atomic weight, approximately 23.

THE Symbol Na is an abbreviation of the words natrium, this being derived from natron, which was from the Greek word nitron, which was the original name of the carbonate. Our English word sodium is derived from soda, which comes from the word sodash, this hinting its preparation from the ashes of "sods," or marine plants.

Sodium, like potassium, was isolated by Sir Humphrey Davy in 1807 by the electrolysis of the hydrate.

Occurrence.—The most abundant source of sodium is common salt, or sodium chloride, this being a constituent of sea-water, but chiefly obtained in commerce either from mines or by the evaporation of brine from salt-wells. Sea-water is a scarcely available source of sodium chloride, because therein are found chlorides of many other elements which are separated with difficulty.

Manufacture. The element sodium is isolated by a process quite similar to that by which we obtain potassium, viz., by heating carbonate with coal, chalk being added as a flux. This process is not so dangerous as is the preparation of potassium, inasmuch as the sodium carbonyl, NaCO, does not solidify in the delivery tube. (See p. 431.) Metallic sodium is now being made by treating sodium hydrate with iron carbide at a temperature of 800° C.

It is also obtained by the electrolysis of sodium hydrate in the same manner employed in isolating potassium.

Properties. Sodium is a soft, silvery-white metal, resembling potassium, and, like it, is so easily oxidized that it must be kept under petroleum. When metallic sodium and mercury are rubbed together, an amalgam results which, when brought into contact with moisture, ignites. This mixture has been used as a cigar-lighter, but its danger was such that it never became popular.

The characteristic tests of the element and its salts are the yellow color that it communicates to a colorless flame; a white precipitate formed when a solution of sodium salt is brought into contact with a solution of pyroantimoniate of potassium.

1 65,000,000

The sodium flame is counted among the most delicate of tests, it having been estimated that grain will respond thereto. By reason of its sensitiveness the positive testing of sodium with the flame is difficult, as almost anything tested will give a yellow flame by reason of the presence of minute traces of sodium. Hence the chemist trains his eye to a rough estimation of the quantity shown. by the intensity of the flame, rather than by the bare fact of the presence of a yellow color.

The following compounds of sodium and their preparations are official: