The formulae of the Ph. D. and Ph. E. are very similar.
2. Add iodine to a hot solution of pure hydrate of potassium until the alkali is perfectly neutralised, carefully avoiding excess; evaporate the liquid to dryness, and expose the dry mass to a gentle red heat in a platinum or iron crucible; afterwards dissolve out the salt, gently evaporate, and crystallise. An excellent process, yielding a large product, but, if the ignition be not carefully managed, it is apt to contain a little undecomposed iodate. To obviate this, Mr Scanlan proposes the addition of a little powdered charcoal to the mass before ignition--a plan adopted in the Ph. U. S.
3. Iodine is treated with a small proportion of phosphorus in water, and is thus converted into 'hydriodic acid,' hydrate of calcium is then added, and the 'iodide of calcium' formed is first fused, and then decomposed by sulphate of potassium into 'sulphate of calcium,' which is precipitated, and 'iodide of potassium,' which remains in solution, and may be crystallised, as in the other processes. This is a modification of a method devised by Liebig.
4. (Ph. B.) Put solution of potash, 1 gall., into a glass or porcelain vessel, and add iodine 29 oz., or q. s., in small quantities at a time, with constant agitation, until the solution acquires a permanent brown tint. Evaporate the whole to dryness in a porcelain dish, pulverise the residue, and mix this intimately with wood charcoal in fine powder, 3 oz.
Throw the mixture, in small quantities at a time, into a red-hot crucible, and when the whole has been brought to a state of fusion, remove the crucible from the fire and pour out its contents. When the fused mass has cooled, dissolve it in 2 pints of boiling distilled water, filter through paper, washing the filter with a little distilled boiling water; unite the liquids, and evaporate till a film forms on the surface. Set aside to cool and crystallise. Drain crystals and dry quickly with a gentle heat; more crystals may be obtained by evaporating the mother liquor, and cooling.
The salt should be kept in a stoppered bottle.
_Prop._ It crystallises in cubes, which in the pure salt are extremely white, though frequently opaque; these are anhydrous; fuse when heated, without decomposition; dissolve in less than an equal weight of water, at 60 Fahr., and very freely in alcohol; and do not deliquesce in moderately dry air unless they contain undecomposed hydrate of potassium. Its solution dissolves the iodine freely, and also, less readily, several of the insoluble metallic iodides and oxides.
_Pur._ It is entirely soluble in both water and alcohol. Its aqueous solution alters the colour of turmeric either not at all or but very slightly, nor does it affect litmus paper, or effervesce with acids.
Nitric acid and starch being added together, it becomes blue. It is not coloured by the addition of tartaric acid with starch. No precipitate occurs on adding either a solution of hydrate of calcium or of chloride of barium. 100 gr., dissolved in water, by the addition of nitrate of silver, yield a precipitate of 141 gr. of iodide of silver.
_Assay._ The iodide of commerce frequently contains fully one half its weight of either chloride or carbonate of potassium, or both of them, with variable quantities of iodate of potassium, a much less valuable salt. The presence of these substances is readily detected by the above tests. As the first of these is only very slightly soluble in cold alcohol, and the others insoluble in that liquid, a ready method of determining the richness of a sample in pure iodide, sufficiently accurate for ordinary purposes, is as follows:--Reduce 50 gr. of the sample to fine powder, introduce this into a test tube with 6 fl. dr. of alcohol, agitate the mixture violently for one minute, and throw the whole on a weighed filter set in a covered funnel, observing to wash what remains on the filter with another fl. dr. of alcohol. The filtrate, evaporated to dryness, gives the quantity of pure iodide, and the filter, dried by the heat of boiling water, that of the impurities present in the sample examined, provided it contained no hydrate of potassium. The quantity of alkali, whether hydrate or carbonate, may be found by the common method of 'alkalimetry.'
_Uses, &c._ Chiefly in photography, medicine, and pharmacy.--_Dose_, 1 to 10 gr., twice or thrice daily, made into pills, or, better, in solution, either alone or combined with iodine; in bronchocele, scrofula, chronic rheumatism, dropsy, syphilis, glandular indurations, and various other glandular diseases. Also externally, made into a lotion or ointment.
=Potassium, Nitrate of.= KNO_{3}. _Syn._ NITRATE OF POTASH, NITRE, SALTPETER; POTASSae NITRAS (B. P., Ph. L., E.,& D.), NITRUM, SAL NITRI, SAL PETRae, KALI NITRATUM, L. This salt is produced naturally in the soil by the action of the atmosphere, and crystallises upon its surface, in various parts of the world, especially in the East Indies. On the Continent it has long been produced artificially, by exposing a mixture of calcareous soil and animal matter to the atmosphere, when calcium nitrate is slowly formed, and is extracted by lixiviation. The liquid is then decomposed by the addition of wood ashes, or carbonate of potassium, by which carbonate of calcium is precipitated, and nitrate of potassium remains in solution. The places where these operations are performed are called 'nitriaries,' or 'nitrieres artificielles.' The British market is wholly supplied from India. The salt of the first crystallisation, by either process, is called 'crude nitre' or 'rough saltpetre.' This is purified by solution in boiling water, skimming, and, after a short time allowed for defecation, straining (while still hot) into wooden crystallising vessels. The crystals thus obtained are called 'single refined nitre,' and when the process is repeated 'double refined nitre.'
1. (POTASSae NITRAS PURUM--Ph. D.) Commercial nitre, 4 lbs.; boiling distilled water, 1 quart; dissolve, withdraw the heat, and stir the solution constantly as it cools; the minute crystals, thus obtained, are to be drained, and washed, in a glass or earthenware percolator, with cold distilled water, until that which trickles through ceases to give a precipitate with a solution of nitrate of silver, the contents of the percolator are then to be withdrawn, and dried in an oven.
_Prop._ White, pellucid, six-sided prisms; permanent in the air; soluble in 7 parts of water at 60 and in 1 part at 212 Fahr.; insoluble in alcohol; its taste is cool, saline, and slightly bitter and pungent; at about 560 it fuses to an oily-looking mass, which concretes on cooling, forming 'sal prunella,' at a red heat it gives out oxygen, and, afterwards, nitrous fumes; sp. gr. 1925 to 1975.
_Pur._ Commercial nitre generally contains chlorides, sulphates, or calcareous salts. The first may be detected by its solution giving a cloudy white precipitate with nitrate of silver. The second by chlorides of barium or calcium giving a white precipitate, and the third by oxalate of ammonium giving a white precipitate.
_Assay._ Of the numerous methods prescribed for this purpose, few are sufficiently simple for mere practical men. The proportion of chlorides, sulphates, and calcareous salts may be determined as above; and the general richness of the sample by the method of Gay-Lussac, modified as follows:--100 gr. of the sample (fairly chosen) are triturated with 50 gr.
of lampblack and 400 gr. of common salt, and the mixture placed in an iron ladle, and ignited or fused therein, due care being taken to prevent loss; the residuum is exhausted with hot water, and the solution thus obtained tested by the usual methods of alkalimetry for carbonate of potassium. The quantity of carbonate found, multiplied by 2125 or 2-1/8, gives the per-centage richness of the sample in nitrate.
_Uses, &c._ Nitre is chiefly employed in the manufacture of gunpowder, fireworks, and nitric acid. It is also used in medicine as a sedative, refrigerant, and diaphoretic, and as a cooling diuretic. It has been recommended in active haemorrhages (especially spitting of blood), in various febrile affections, in scurvy, and in herpetic eruptions; and it has been highly extolled by Dr Basham as a remedy in acute rheumatism.--_Dose_, 5 to 15 gr., every 2 hours. A small piece, dissolved slowly in the mouth, frequently stops a sore throat at the commencement.
In large doses it is poisonous. The best treatment is a powerful emetic, followed by opiates.
=Potassium, Nitrite of.= KNO_{2}. _Syn._ NITRITE OF POTASSA; POTASSae NITRIS, L. _Prep._ 1. By heating nitre to redness, dissolving the fused mass in a little water, and adding twice the volume of the solution in alcohol; after a few hours the upper stratum of liquid is decanted, and the lower one, separated from the crystals, evaporated to dryness.
2. (Corenwinder.) Nitric acid, 10 parts, are poured on starch, 1 part, and the evolved gas passed through a solution of hydrate of potassium of the sp. gr. 1380, to saturation; the liquid is then either neutralised with a little hydrate of potassium (if necessary), and kept in the liquid form, or at once evaporated. Fused pinkish mass, or clear colourless soluble crystals, used in chemistry as a reagent, and deoxidiser.
=Potassium, Oxalate of.= K_{2}C_{2}O_{4}. _Syn._ NEUTRAL OXALATE OF POTASSA; POTASSae OXALAS, L. _Prep._ Neutralise a solution of oxalic acid, or the acid oxalates, with carbonate of potassium, evaporate, and crystallise. Transparent colourless rhombic prisms, soluble in 3 parts of water, and of the formula K_{2}C_{2}O_{4},Aq.
=Potassium, Hydrogen Oxalate of.= KHC_{2}O_{4}. _Syn._ POTASSIUM BINOXALATE, SALT OF SORREL, ESSENTIAL SALT OF LEMONS; POTASSae BINOXALAS, L. _Prep._ By saturating a solution of oxalic acid, 1 part, with carbonate of potassium, adding to the mixture a similar solution of 1 part of oxalic acid, unneutralised, and evaporating for crystals. It may also be obtained from the expressed juice of wood or sheep's sorrel, by clarifying it with eggs or milk, and evaporating, &c., as before. Colourless rhombic crystals of the formula KHC_{2}O_{4},Aq., soluble in 40 parts of cold and 6 parts of boiling water, yielding a very sour solution.
=Potassium, Trihydrogen Oxalate of.= KH_{3}(C_{2}O_{4}), or KHC_{2}O_{4}, H_{2}C_{2}O_{4}. _Syn._ POTASSIUM QUADROXALATE, POTASSIUM ACID OXALATE.
_Prep._ By neutralising 1 part of oxalic acid with carbonate of potassium, adding to the solution 3 parts more of oxalic acid, evaporating and crystallising. Resembles the last; has the formula KH_{3}(C_{3}O_{4})_{2},2Aq; but is less soluble, and more intensely sour, and forms modified octahedral crystals. The salt is occasionally sold under the names of 'sal acetosellae,' 'salt of sorrel,' and 'essential salt of lemons.' Both are used to remove ink and iron stains from linen, to bleach the straw used for making bonnets, and, occasionally, in medicine, as a refrigerant.
=Potassium, Oxide of.= K_{2}O. _Prep._ Burn pure potassium in a current of oxygen. White powder, rapidly absorbing water and forming the hydrate.
=Potassium, Perchlorate of.= KClO_{4}. _Syn._ POTASSae PERCHLORAS, L.
Prepared by projecting well-dried and finely powdered chlorate of potassium in small portions at a time, into warm nitric acid. The salt is separated from the 'nitrate' by crystallisation.
=Potassium, Prus'siate of.= See POTASSIUM FERRICYANIDE and FERROCYANIDE.
=Potassium, Salicylite of.= Formed by mixing salicylous acid (artificial oil of meadow-sweet) with a strong solution of hydrate of potassium; it separates, on agitation, as a yellow crystalline mass, which, after pressure in bibulous paper, is recrystallised from alcohol. Golden-yellow crystals, soluble in both water and alcohol; damp air gradually converts them into acetate of potassium and melanic acid.
=Potassium, Silicate of.= (Ure.) _Syn._ POTASSae SILICAS. _Prep._ Mix 1 part of powdered quartz or flint, or of fine siliceous sand with 2 parts of carbonate of potash, and fuse them in a Hessian crucible. Dissolve the mass in water, filter the solution and evaporate it to dryness--_Dose_, 10 gr. to 15 gr. in 6 or 8 oz. of water, twice a day. To dissolve gout concretions. An impure silicate of potash is used as a water-glass.
=Potassium, Sulphate of.= K_{2}SO_{4}. _Syn._ POTASSae SULPHAS (B. P., Ph.
L., E., & D.). _Prep._ The sulphate of potassium of commerce is a secondary product of several chemical and manufacturing processes. Thus, the residuum of the distillation of nitric acid from nitre is dissolved in water, the solution neutralised with carbonate of potassium, and, after defecation, evaporation until a pellicle forms; it is then strained, or decanted, and set aside to crystallise. Or, the residuum is simply ignited, to expel excess of acid, and then dissolved and crystallised as before.
_Prop., &c._ Anhydrous, heavy, quartz-like crystals; permanent in the air; soluble in 12 parts of water at 60 and in 5 parts at 212 Fahr.; insoluble in alcohol; extremely nauseous, and bitter-tasted. It crepitates on the application of heat; fuses at a red heat, but loses nothing in weight. 100 gr. dissolved in distilled water, on the addition of chloride of barium and hydrochloric acid, furnish 132 gr. of sulphate of barium, dried at a red heat.
=Potassium, Bisulphate of.= KHSO_{4}. _Syn._ POTASSIUM-HYDROGEN SULPHATE, ACID POTASSIUM SULPHATE; POTASSae BISULPHAS. _Prep._ 1. (Anhydrous.) Neutral sulphate of potassium and oil of vitriol, equal parts; hot water, q. s. (not more) to dissolve; anhydrous bisulphate crystallises out, in long delicate needles, as the solution cools. If these are left for several days in the mother-liquor they are redissolved, and crystals of the ordinary hydrated bisulphate are deposited.
2. (Hydrated,)--_a._ (Ph. L. 1836.) Salt left in distilling nitric acid, 2 lbs.; boiling water, 3 quarts; dissolve; add of sulphuric acid 1 lb.; concentrate by evaporation, and set the liquid aside, so that crystals may form.
_b._ (Ph. D.) Sulphate of potassium (in powder), 3 oz.; sulphuric acid, 1 fl. oz.; mix them in a porcelain capsule, and expose it to a heat capable of liquefying its contents, until acid vapours cease to be evolved; powder the residuum, and preserve it in a well-stopped bottle.
_Prop., &c._ Sour and slightly bitter-tasted rhombic prisms; soluble in about 2 parts of cold and 1 part of boiling water, the solution exhibiting a strongly acid reaction. It is much employed, in lieu of tartaric acid, for the production of carbonic acid, in 'gazogenes,' &c.; also to adulterate cream of tartar and tartaric acid. According to Dr Paris, it forms a "grateful adjunct to rhubarb."--_Dose_, 12 gr. to 1-1/2 dr., in solution, combined with rhubarb or bitters, as the neutral sulphate.
=Potassium, Sulphide of.= _Syn._ SULPHURET OF POTASSIUM, LIVER OF SULPHUR; POTASSII SULPHURETUM (Ph. L., E., & U. S.), HEPAR SULPHURIS (Ph.
D.), L. _Prep._ 1. (Ph. E.) Sulphur, 1 oz.; carbonate of potassium, 4 oz.; mix, heat them in a covered crucible till they form a uniform fused mass; when cold, break it into fragments, and preserve it in well-closed vessels. The formulae of the Ph. L. 1836 and Ph. U. S. are similar.
2. (Ph. D.) Sublimed sulphur, 4 oz.; carbonate of potassium (from pearlash, first dried, and then reduced to powder), 7 oz.; mix in a warm mortar, heat them in a Hessian crucible, as before, pour the fused mass into an iron cup, over which immediately invert a second vessel, to exclude the air, and, when cold, break the mass into fragments, and preserve it in a green-glass stoppered bottle.
_Prop., &c._ A hard, brittle, liver or greenish-brown coloured solid; inodorous whilst dry; soluble in water, forming a highly-fetid solution; and, in acids, evolving strong fumes of sulphuretted hydrogen; reaction, alkaline; exposed to the air, it is gradually converted into sulphate of potassa. As a medicine it is reputed diaphoretic, expectorant, and stimulant.--_Dose_, 2 to 6 gr., in solution, or made into pills with soap; in gout, rheumatism, liver affections, and various chronic skin diseases.
Externally, made into a lotion and ointment. It is highly acrid and corrosive, and in large doses poisonous.
=Potassium, Sulphocyanide of.= KCNS, or KCyS. _Syn._ SULPHO-CYANURET OF POTASSIUM; POTASSII SULPHOCYANIDUM, P. SULPHO-CYANURETUM, L. _Prep._ 1.
Ferrocyanide of potassium (anhydrous, or dried by a gentle heat), 46 parts; sulphur, 32 parts; pure carbonate of potassium, 17 parts; reduce them to powder, and very gradually heat the mixture to low redness in a covered iron crucible, which it will less than one half fill; remove the half-refrigerated and still soft mass, crush it, exhaust it with water, and evaporate the aqueous solution to dryness; powder the residuum, and exhaust it with hot alcohol or rectified spirit; the alcoholic solution will yield beautiful white crystals as it cools, and the residuum or mother-liquor may be evaporated for the remainder of the salt.
2. Cyanide of potassium, 3 parts; sulphur, 1 part; water, 6 parts; digest them together for some time, add 3 parts more of water, filter, evaporate, and crystallise.
_Prop., &c._ Long, slender, colourless prisms or plates, which are anhydrous, bitter-tasted, deliquescent, fusible, very soluble in both water and alcohol, and non-poisonous. It is chiefly used as a test for ferric oxide, for which purpose it is preferable to all other substances.
=Potassium, Tartrate of.= K_{2}C_{4}H_{4}O_{6}. _Syn._ NEUTRAL TARTRATE OF POTASSIUM, TARTRATE OF POTASSA, NEUTRAL TARTAR, SOLUBLE T.; POTASSae TARTRAS (B. P., Ph. L., E., & D.), KALI TARTARIZATUM, L. _Prep._ (Ph. D.) Carbonate of potassium, 8 oz.; distilled water, 2 quarts; dissolve, and to the solution, whilst boiling hot, gradually add of bitartrate of potassium, in fine powder, 1 lb., or q. s., so that the liquid, after ebullition for a couple of minutes, ceases to change the colour of either blue or reddened litmus paper; next filter the liquid through calico, evaporate it until a pellicle forms on the surface, and set it aside to crystallise; after 12 hours collect the crystals, dry them on bibulous paper, and preserve them from the air. The formula of the Ph. L. 1836 is nearly similar.
_Prop., &c._ The crystals of this salt, which are obtained with difficulty, are right rhombic prisms, and are deliquescent. The salt of commerce is usually in the form of a white granular powder, which is obtained by simply evaporating the solution to dryness, with constant stirring. In this state it requires about 4 parts of cold water for its solution. Acids convert it into the bitartrate. As a medicine it acts as a gentle diuretic and aperient, and is valued for correcting the griping properties of senna and resinous purgatives. It is also antiscorbutic.--_Dose_, 1/2 dr. to 3/4 oz., in powder, or dissolved in water. The solution changes the colour neither of litmus nor turmeric. The addition of almost any acid throws down crystals of bitartrate of potassium, which generally adhere to the vessel. The precipitate occasioned by either chloride of barium or acetate of lead is dissolved by dilute nitric acid.
=Potassium, Bitartrate of.= KHC_{4}H_{4}O_{6}. _Syn._ ACID TARTRATE OF POTASSA, SUPER-TARTRATE OF P., CREAM OF TARTAR; CREMOR TARTARI, POTASSae BITARTRAS (B. P., Ph. L., E., & D.), POTASSae SUPER-TARTRAS, TARTARI CRYSTALLI, L. This well-known salt is deposited during the fermentation of grape juice as a crust on the sides of the casks or vats. In its unprepared or crude state it is called white or red tartar or argol, according to the wine from which it has been obtained. It is purified by boiling it in water, crystallisation, re-solution in water, and treatment with freshly burnt charcoal and aluminous clay, to remove the colour; the clear liquid is then decanted, whilst still hot, and allowed to cool slowly; the resulting crystals form the 'cream of tartar' of commerce.
_Prop., &c._ Small, translucent, gritty, prismatic crystals, irregularly grouped together; permanent in the air; requiring fully 100 parts of cold water, and about 15 parts of boiling water, for their perfect solution; the solution has a harsh, sour taste, and, like that of the tartrate, suffers spontaneous decomposition by keeping. Its solution reddens litmus.
At a red heat it is converted into carbonate of potassium. Entirely soluble in 40 parts of boiling water; 40 gr., in solution, are neutralised by 30 gr. of crystallised carbonate of soda.--_Dose._ As an aperient, 1 to 3 dr.; as a diuretic, 1/2 dr. to 1 dr.; as an antiscorbutic, 10 to 20 gr.
frequently. It is much used to make a pleasant cooling drink ('Imperial'), and in tooth-powders.
=POTA'TO.= This well-known and valuable article of food is the tuber of the _Solanum tuberosum_ or _esculentum_, a plant which was introduced to this country by either Sir Francis Drake or Sir Walter Raleigh, towards the latter part of the 16th century. It is now extensively cultivated in all the temperate climates of the world. It yields a vast quantity of food on a small space of ground, but only about 1-7th part of the weight of the tuber is nutritious, and this is chiefly farinaceous. Its farina or starch is, however, accompanied by no inconsiderable portion of saline matter, more especially of potassa, which renders it highly antiscorbutic, and a powerful corrective of the grossness of animal food. When forming part of a mixed diet, perhaps no substance is more wholesome than the potato, and, certainly, no other esculent hitherto discovered appears equally adapted for universal use.
Boussingault gives the following as the average composition of the tubers of the potato:--
Moist Dry.
Water 759 -- Albumen 23 96 Oily matter 02 08 Fibre 04 17 Starch 202 838 Salts 10 41 ------ ------ 1000 1000