; . : kBBT M. 



FOTASSirM. 



pound of a grayish odour ; it is tamed M rt>0 i J""**" 1 '! and when 

 dsssolTc.1 in mtar yield* eroconato and rAerfuoMfe of potaah. 



r-Qlmrinm luu so intense an affinity for other element* that U .!,. 

 not occur in nature in the free state. In combination, however, it 

 it frequently met with. Nearly all land plant* contain it, derived 

 mainly from disintegration of feldspar their aahea consequently yield 

 much carbonate of potwh ; aea-water also contain* a nnall quantity 

 of potaah salts, and nitrate of potaah occun native in large quantities! 

 a* an efflorescence from the soil in warm climates. [POTASSIUM, 

 M. HIM. Dtv.J 



Potassium U a bluiah-white metal of *p. g. 0-865. At 32 Fahr. 

 it U brittle, and ha* a crystalline fracture ; at ordinary temperature* 

 it i* quite soft, and at 130* Kahr. it in liquid. A freshly cut sur- 

 faoe poa*e**e* high metallic lustre, but it almost instantly become* 

 covered with a coating of white nut It may be preserved in tin' 

 bright state by melting it in one end of a glass tube, from which the 

 air ha* been expelled by a current of hydrogen, or coal gas, and then 

 allowing it to flow down to the other end of the tube, passing in it* 

 course through a small piece of wire gauze; the dross is thim 

 filtered away and the metal obtained in a brilliant lustrous condition. 

 On fusing off, by the aid of a blow-pipe, that part of the tube con- 

 taining the gauze, Ac., then melting the potassium and allowing it 

 to cool very slowly, and when partly solidified rapidly pouring off 

 the liquid portion, the solid potassium is obtained crystallised in 

 quadratic octohedra. 



Potassium has a great affinity for oxygen. It will toko that taunt 

 out of almost any combination. Thrown on to the surface of water 

 it rapidly becomes converted into oxide of potassium, and generate* 

 sufficient heat to ignite the hydrogen that is set free, the latter 

 carrying off a little vapour of potassium and burning with a beau- 

 tiful violet flame. At an elevated temperature potassium decomposes 

 carbonic oxide, carbonic acid, or any gas that contains oxygen. In 

 chemical research potassium is frequently used for removing the 

 las* traces of oxygen from a hydrocarbon liquid, by rectifying the 

 latter over a small quantity of the metal. From what ha* been said 

 it is evident that potassium must always be kept in purified rock 

 oil, or naphtha, or some liquid that contains no oxygen. 



The equivalent of potassium is 38-96. 



Polonium and oxygen form three compounds : 



1. Suboxide of potassium K 2 OJ 



i. Protoxide of potassium kll 



3. Teroxide of potassium KO, 



1. Suboxide of potattium. This is formed when potassium is ex- 

 posed in a close vessel to a very email quantity of air. It is very 

 unstable, and is probably only a mixture of metal and protoxide. 



2. Protoxide of potattium (KO). Potath ; potatta. This an/ii/iln/im 

 oxide is formed when the metal is exposed to perfectly dry air ; or 

 when equivalent weight* of water and potassium are brought together 

 in a vessel from which air is excluded. It is very deliquescent, and 

 when moistened with water becomes incandescent. 



llytlraled oxide of potattium (KO,HO). Potath ; cauttic potath. 

 This is best prepared by dissolving carbonate of potash in ten times 

 its weight of water and then gradually adding half its weight of 

 quick-lime, previously slaked and made into a cream with water ; 

 carbonate of lime deposits, and caustic potash remains in solution. 

 The resulting liquid frequently contains alumina. Solid hydrate of 

 potash is obtained on evaporating the liquor, just mentioned, until the 

 residue remains in a state of tranquil fusion ; it was formerly called 

 lapii ifemalui. It crystallises in acute rhombohvdra. The following 

 is Dalton's table of the strength and boiling point of caustic potash 

 solutions of different specific gravities : 



Anhydrous PoUsh (KO). 



gfwtiae gravity. Per cent. Uniting Point. 



1-88 il-2 ill" Fabr. 



1-60 48-7 110 



I'M 41-t 276 



I -47 185 



1-44 8-8 JS4" 



41 14-4 246' 



it 31-4 



M !9-4 234 



13 26-3 229* 



IK 2S-4 224' 



2 It'S 220' 



It 18'1 218' 



II IS'O 2IS 



II ' 214' 



I'M 4-7 211 



The Honor irtatKt of the London Pharmacopoeia has a density of 



8. Teroxide of potamm (KO,) in formed when the metal is burned 

 in exonss of oxygen gas, or when caustic potash U fused in contact with 

 air. It is a yellowish brown substance, having a crystalline texture, 

 and readily parts with its oxygtn to combustibles, and even on 

 dissolving in water. 



tum and phoipkonu may be fused together under r<-< 

 with production of a chocolate-brown phosphide of potassium. Water 

 decomposes it into hypophosphite of potash and into gaseous and 



liil pbosphuretted hydrogen. 



Potatrint* and lulptittr form five different compounds, namely : 



1 . Prutonulphklc of potassium 



2. Bisulphide of potaulum 



3. Trrsulphlde of potassium 



4. Tetrasulphidc of potassium . 

 9. 1'rntasulphide of potassium 



KS 



1. The first is formed on heating sulphate of potash in a current of 

 hydrogen. Its colour i* yull<>wili-brown, it is very deliquescent, and 

 cauterises the xkin. -.'. Tim second is formed on passing excess of 

 sulphuretted hydrogen through an alcoholic solution of potash, evapo- 

 rating in the air till it becomes turbid, and then exposing it in vacua. 

 It is fusible, and of an orange colour. 3. Tersulphide of potassium is 

 obtained on passing Usubphld* of carbon vapour over ignited carbonate 

 of potash. 4. Tli.- t<-ti;wiilpliidi> results when bisulphide of carbon 

 vapour is passed over ignited sulphate of potash. 5. Pcntasulphide of 

 potassium is formed when a solution of any of flic preceding sulphides 

 i- In.ili-d with excess of milphur; or, mixed with other potash salts, 

 when caustic potash is 1..-1I..I \\ith excess of Milphur ; or when car- 

 bonate of potash is fused with excess of sulphur. Lirrr f tul/i/iur is 

 an old preparation, made by fusing together 69 parts of carbonate of 

 potash with 40 of sulphur; it is mainly a mixture of sulphate of 

 potash and tersulphide of potassium. With the exception of the first, 

 all the above sulphides of potassium yield sulphuretted hydrogen and 

 free sulphur on being decomposed by a dilute acid, thus : 



KS. + HC1 =KC1 + IIS + 8^,. 



Polonium and iilcnluin form compounds apparently resembling the 

 sulphides. 



Polonium and iodine form only one compound, namely, 

 Iodide of potattium (KI). J/ydriodate of potath. This salt is uni.-li 

 used in medicine. It may be made by dissolving iodine in caustic 

 potash, evaporating to dryness, and gently igniting the residue to drive 

 off the oxygen from the lodate of potash that is produced at the same 

 time : 



6KO + I, = 5KI + KO, IO, 



Potash. 



Iodine. 



Iodide of 

 potassium. 



Or it may be formed by fusing iodine with excess of iron, decom- 

 posing the iodide of iron solution by carbonate of potash, filtering, and 

 evaporating to the crystallising point. 



;FcI + KO, CO, = FeO, CO, + KI 



Iodide of 

 iron. 



Iodide of 

 potassium. 



Iodide of potassium crystallises in white cubes, having a cooling 

 somewhat bitter taste. It is very soluble in water, and, if pure, com- 

 pletely dissolves in six times its weight of alcohol. It readily dissolves 

 iodine, forming a deep brown solution. 



Potassium and bromine form bromide of potattium (KBr). It may be 

 prepared by the same methods as the iodide, substituting bromine for 

 iodine. Its appearance is also similar. 



Pola.-du.m and chlorine form 



('/ilia-ide of potattium (KC1). Potassium burns in chlorine with 

 even greater brilliancy than in oxygen ; the product is chloride of 

 potassium. This salt may also be fanned by dissolving carbonate of 

 potash in hydrochloric acid, and evaporating to the crystallising point. 

 Chloride of potassium is a bye-product in many pharmaceutical and 

 chemical operations, and, from the facility with which it may be 

 decomposed, is useful as a source of other potash salts. 



Potattium decompose* hydrofluoric acid, and forms fluoride of 

 potattium (KF). It crystallise* in cubes. 



*il leu-fluoride of potattium (KF, SiF,) falls as a transparent gela- 

 tinous precipitate on adding hydrofluosUicic acid to a salt of potash. Its 

 formation is sometimes used as a test for potash. 



CarlioMole of potath (KO, CO,). This salt is imported in large quan- 

 tities from Itussia and America. It is procured from plants, which |.n- 

 this purpose are burned in dry pits three or four feet deep, the ashes 

 dissolved in water, evaporated until the phospliates, sulphates, chlo- 

 rides, Ac., crystalline out, and the mother liquor then boiled to dry- 

 ness. Such is the crude potath or pearUuh of commerce ; it varies 

 very much in quality, but its value is always determined by the 

 process of Ai.KALiMETirv. After rccrystaUisation till purr, it is sent 

 into the market as Haiti of tartar, or purified pearlathet. 



Chemically pure carbonate of potash may be obtained by heating 

 the bicarbonate to a little below redness, or by deflagrating a mixture 

 of equal port* of nitrate and bitartrate of potash : i-itli. 

 digested in water, filtered, and evaporated to the crystallising point. 



Carbonate of potash crystallises in deliquescent, <>l>]i.|i:<>, rli.nnlii.- 

 octohedra, containing two oquivalvuU of water of crystallisation t K O 



