POTASH. 



667 



in small vials under naphtha, or oil of copaiba. It 

 conducts electricity, like the common metals. 

 When thrown upon water, it acts with great vio- 

 lence, and swims rapidly upon the surface, burning 

 with a beautiful light of a red colour, mixed with 

 violet. The water becomes a solution of potasii. 

 When moderately heated in the air, it inflames, burns 

 with a red light, and throws oft' alkaline fumes. 

 Placed in chlorine, it burns with great brilliancy. 

 On all fluids containing much water, oxygen, or 

 chlorine, it readily acts. It combines with oxygen 

 in two proportions. The protoxide is the pure 

 potash above described, and consists of potassium 

 40 and oxygen 8. When potassium burns in open 

 air, or in oxygen gas, it is converted into an orange- 

 coloured substance, which is the peroxide of potas- 

 sium. It may also be formed by conducting oxygen 

 gas over potash at a red heat. It consists of potas- 

 sium 40 and oxygen 24. The attraction of chlorine 

 for potassium is much stronger than that of oxygen 

 for this metal. Chloride of potassium has a saline 

 and bitter taste. It is composed of 36 parts of 

 chlorine and 40 of potassium. The iodide of potas- 

 sium is formed with the emission of light, when 

 potassium is heated in contact with iodine. It 

 fuses readily when heated, and is volatilized at a 

 temperature below redness. It dissolves in strong 

 alcohol; and the solution, when gently evaporated, 

 yields small colourless cubic crystals of iodide of 

 potassium. It is composed of 124 iodine and 40 

 potassium. Hydrogen and potassium unite in two 

 proportions, forming in one case a solid, and in the 

 other a gaseous compound. The latter is produced, 

 when hydrate of potash is decomposed by iron at a 

 white heat ; and it appears also when potassium is 

 burned on the surface of water. It is called potas- 

 sureted hydrogen. It inflames spontaneously in 

 air or oxygen gas ; but on standing for some hours 

 over mercury, the greater part, if not the whole, of 

 the potassium is deposited. The solid compound 

 of these bodies, called hydroguret of potassium, is 

 formed by heating potassium in hydrogen gas. It 

 is a grey, solid substance, which is readily decom- 

 posed by heat, or contact with water, but does not 

 inflame spontaneously in oxygen gas. By the aid 

 of a little heat, sulphur unites readily with potas- 

 sium, and forms a sulphuret of this metal ; and so 

 much caloric is evolved at the moment of combina- 

 tion, that the mass becomes incandescent. It has 

 a red colour, fuses before the temperature of igni- 

 tion, and assumes a crystalline texture in cooling. 

 It consists of sulphur 16 and potassium 40. Phos- 

 phuret of potassium may be formed in like manner 

 by the action of potassium on phosphorus, with the 

 aid of a moderate heat. Charcoal, which has been 

 strongly heated in contact with potassium, effervesces 

 in water, rendering it alkaline, though the charcoal 

 may be previously exposed to a temperature at 

 which potassium is volatilized. Hence there is 

 probably a compound of the two formed by a 

 feeble attraction. 



We now return to the subject of potash, or the 

 protoxide of potassium, whose importance in a 

 state of purity and in the compounds it forms with 

 the acids, is so great to mankind. Potash is acted 

 on by phosphorus. When it is heated in a close 

 tube with phosphorus, a compound is formed, 

 which, when thrown into water, decomposes it, 

 phosphoric acid remaining in solution, and phos- 

 phureted hydrogen being liberated. The nature of 

 this compound is yet uncertain ; it may either be 

 a phosphuret of potash, or a mixture of phosphate 

 of potash and phosphuret of potassium. 



Sulphuret of potash, it used to be imagined, was 

 formed when eoual parts of sulphur and dry .con- 



crete potash are heated in a covered crucible, or 

 when one part of sulphur and two parts of sub-car- 

 bonate of potash are heated together. But the 

 usual product of these methods is sulphuret of 

 potassium. It is said, however, that if the heat be 

 kept moderate, a proper sulphuret of potash is 

 formed. It is inodorus while dry ; but when mois- 

 tened or dissolved, acquires a fetid smell, from the 

 production of sulphureted hydrogen. From suffer- 

 ing decomposition when in a state of solution, it is 

 scarcely possible to discover precisely its peculiar 

 agencies. 



Hydrosulphuret of potash is formed by transmit- 

 ting sulphureted hydrogen through a solution of 

 potash. It is obtained in large prismatic crystals, 

 white and transparent ; its taste is alkaline and 

 bitter. It attracts humidity from the air, and is 

 soluble both in water and alcohol. 



Carbonate, or sub carbonate of potash. This is 

 the pearl ashes of commerce. It is obtained from 

 heating the crude potash in a reverberatory furnace, 

 and stirring it briskly for some time at a white 

 heat. From the predominance of the alkali in it, 

 it is deliquescent ; if exposed to the air, it soon 

 attracts its weight of water, which is the quantity 

 necessary for its complete solution. Its taste is 

 acrid ; it changes the vegetable colours to green, 

 and combines with oils. These characters are so 

 distinctly alkaline, that they formerly led to the 

 opinion, that the potash was in excess in the salt, 

 and hence it was termed a sub-carbonate ; they 

 are, however, to be ascribed rather to the weak 

 acidity of the carbonic acid than to deficiency in its 

 proportion ; for it is proved that the salt consists of 

 carbonic acid 22 and potash 48 ; hence it is strictly 

 a carbonate of potash. It is decomposed by the 

 acids; its carbonate acid being disengaged with 

 effervescence. 



The bicarbonate of potash may be obtained by 

 exposing the solution of the carbonate to the air 

 for some time, carbonic acid being imbibed from 

 the atmosphere, and crystals being deposited ; or it 

 is formed more directly by passing a current of 

 carbonic acid gas through a solution of the carbon- 

 ate of such a strength that crystals form spontane- 

 ously. They are much more soluble in hot water, 

 the water taking up five sixths of its weight ; but, 

 if the temperature be that of boiling water, part of 

 the carbonic acid assumes the elastic state, and 

 rises through the liquor. The taste of this salt is 

 more mild than that of the pearl ashes ; though still 

 alkaline, it has no causticity, but it changes the 

 vegetable colours to a green. It contains just 

 double the quantity of carbonic acid in the carbon- 

 ate of potash. It is much used for medicinal pur- 

 poses. 



Nitrate of potash, nitre, or saltpetre, is a white, 

 translucent, or transparent salt, usually crystallized 

 in distinct six-sided prisms, with dihedral summits. 

 Its taste is penetrating; but the cold produced by 

 placing the salt to dissolve in the mouth, is such as 

 at first to predominate over the acid. Seven parts 

 of water dissolve two of nitre, at the temperature 

 of 60; but boiling water dissolves its own weight. 

 Its constituents are nearly equal weights of nitric 

 acid and potash. On being exposed to a gentle 

 heat, it fuses ; and in this state being poured into 

 moulds, so as to forw little round cakes, or balls, 

 it is called sal prunella, or crystal mineral. Nitre 

 powerfully promotes the combustion of inflammable 

 substances. Two or three parts, mixed with one 

 of charcoal, and set on fire, burn rapidly ; nitrogen 

 and carbonic acid gas are given out ; and a small 

 portion of the latter is retained by the alkaline 

 residuum, which was formerly called clyssus of 



