POTASSIUM 



353 



volatilises at a very high temperature. It is 

 soluble in about half its weight either of water or 

 of alcohol, and rapidly absorbs both carbonic acid 

 and moisture from the atmosphere. It acts as a 

 powerful caustic, and quickly destroys both animal 

 and vegetable tissues, and hence its solutions can 

 only be filtered through asbestos or pounded glass 

 or sand. Its affinities are so powerful that few 

 vessels are capable of resisting its influence. Its 

 solution must be preserved in glass bottles into 

 the composition of which no oxide of lead enters, 

 as it has the property of dissolving this oxide 

 out of the glass. Vessels containing silica ( porce- 

 lain, earthenware, &c. ) are decomposed, and plat- 

 inum itself is oxidised when heated in contact 

 with it. 



The salts which potash forms with acids are for 

 the most part readily soluble in water, and colour- 

 less, unless (as, for example, in permanganate of 

 potash) the acid is coloured. Most of them are 

 crystallisable, and they all communicate a violet 

 tint, characteristic of potash, to the ttaine of spirit 

 of wine and to that of the blowpipe. Many of 

 them occur in animals and vegetables, and the 

 ashes of plants contain them in large quantity. 



Carbonate of Potash, K,CO 3 , is obtained by 

 burning plants in dry pits, dissolving the ashes in 

 water, evaporating till the sulphates, chlorides, &c. 

 separate in crystals, and then boiling the mother 

 liquid to dryness in iron pots. The quantity of 

 pure carbonate of potash contained in it is liable to 

 great variation, and for pharmaceutical purposes 

 it must be dissolved in water and crystallised, the 

 crystals containing about 20 per cent, of water. 

 Carl>onate of potash is extremely deliquescent, and 

 is soluble in less than its own weight of water, but 

 is insoluble in alcohol. It has an acrid, alkaline 

 ta~te, and its reaction upon test-paper is strongly 

 alkaline. It is a compound of great importance, 

 both as a chemical reagent and as entering largely 

 into the preparation of most of the other compounds 

 of potash, and into the manufacture of soap and 

 class. The commercial carbonate is often called 

 Pearl Ashen. Bicarbonate of Potash, KHCO 3 , is 

 obtained in white rhombic prisms, by passing a 

 current of carbonic acid gas through a strong solu- 

 tion of carbonate of potash. These crystals are per- 

 manent in the air, but are decomposed by heat ; water 

 and carbonic acid being evolved, and the simple 

 carbonate left. This salt is much less soluble than 

 the carbonate, requiring four parts of cold water 

 for its solution, which is nearly neutral to test- 

 paper, and has a much milder taste than the preced- 

 ing salt. It is employed as an antacid in medicine. 

 The Sulphate, K*SO V and /;/,//,/,, ,te, KHSO 4 , may 

 be prepared by treating potash with sulphuric acid. 

 Nitrate of Potash has been already descril>ed under 

 the head NlTRE. Chlorate of Potash, KCIOj, 

 occurs in white rhomboidal tablets of a pearly 

 lustre. It has a cooling taste like that of nitre. 

 It fuses at a gentle heat without decomposition, 

 but on increasing the heat it gradually gives off 

 all its oxygen, and is converted into chloride of 

 potassium, according to the equation : 



Chlorate of Potash. Chloride of Potassium. 



2KC1O, 



2KC1 



Oxygen. 

 3O~ 



It is not very soluble, as it requires for solution 

 16 parts of cold and 1 "7 parts of Ixjiling water. It 

 even surpasses nitrate of potash as an oxidising 

 agent ; and if combustible substances, such as 

 carbon, sulphur, or phosphorus, lie heated or 

 forcibly rubbed with it, a detonation or explosion 

 occurs. This salt i* employed in the manufacture 

 of Matches (q.v. ), in certain operations in calico- 

 printing, and for filling the friction -tubes employed 

 for firing cannon : the best mixture for these tubes 

 consisting of 2 parts of this salt, 2 of sulphide 

 387 



of antimony, and 1 of powdered glass. A mixture 

 known as White Gunpowder, consisting of chlorate 

 of potash, dried ferrocyanide of potassium, and 

 sugar, has been employed for blasting purposes, 

 but its preparation is accompanied by so much 

 danger that it is seldom used. This salt does not 

 occur as a natural product, but may be obtained 

 along with chloride of potassium by passing a 

 current of chlorine gas through a hot solution of 

 caustic potash. The two salts are easily separated 

 by crystallisation, as the chlorate is comparatively 

 insoluble, and the chloride extremely soluble. 

 Hypochlorite of Potash can only be obtained in 

 solution. Under the title of Eau de Javelle, it is 

 sold as a bleaching agent. It is obtained by pass- 

 ing chlorine gas through a cold dilute solution of 

 carbonate of potash, when chloride of potassium 

 and hypochlonte of potash are formed, from which 

 the chloride may be removed by crystallisation. 

 The Phosphates of Potash, formed by the different 

 varieties of phosphoric acid, are sufficiently noticed 

 in the articles PHOSPHORUS and MANURE. The 

 Silicates of Potash are important compounds in 

 connection with the manufacture of glass ; they 

 also enter into the composition of Fucns's Soluble 

 Glass ( see GLASS ), or Water-glass, and have been 

 employed as a coating by which the decay of 

 magnesian and other limestones may be pre- 

 vented. The Chromate and Bichromate of Potash 

 are noticed in the articles CHROMIUM and CALICO- 

 PRINTING. The haloid salts of potassium may 

 be passed over very briefly. The Chloride of 

 Potassium, KC1, is obtained in large quantity in 

 the preparation of chlorate of potash, or may be 

 procured by burning potassium in chlorine gas, 

 when the result of the brilliant combustion which 

 takes place is this salt. In its general characters 

 it closely resembles common salt, NaCl, except 

 that the former communicates a violet and the 

 latter a yellow tint to the flame of alcohol. It 

 is a constituent of sea-water, of salt marshes, 

 and of many animal and vegetable fluids and 

 tissues. The Bromide and Iodide of Potassium are 

 noticed in the articles BROMINE and IODINE. 

 Fluoride of Potassium, KFI, possesses the property 

 of corroding glass. There are several sulphides, 

 the most important being the Liver of Sulphur, 

 prepared by fusing together carbonate of potash 

 anil sulphur. Besides its use in skin diseases, it is 

 much employed by florists to prevent mildew on 

 roses. The Yellow and the Red Prussiate (or the 

 Ferrocyanide and Fcrriryiinide) of Potash are 

 noticed in the article FERRIDCYANOGEN. The 

 Cyanide, of Potassium, KCy, may be obtained com- 

 mercially oy fusing together 8 parts of ferrocyanide 

 and 3 of cartwnate of ]K>tassium. This salt forms 

 colourlessdeliquescent crystals very soluble in water. 

 1 1 exhales an odourof hydrocyanicacid, and is nearly 

 as poisonous as that acid. Its great deoxidising 

 power at a high temperature renders it a valuable 

 agent in many of the finer operations of metallurgy; 

 in ;i dilute solution, it is a solvent for natural gold, 

 and is used (the 'cyanide process ') for the profitable 

 treatmentof low-grade free-milling ores, in which the 

 gold occurs in line particles, nototherwise utilisable. 

 The following are the ordinary tests for the 

 potassium compounds : ( 1 ) Solution of tartaric acid 

 added in excess to a moderately strong solution of 

 a potassium salt gives after some time a white 

 crystalline precipitate of cream of tartar (see TAR- 

 TARIC ACID). The result is hastened by stirring 

 or shaking. (2) Solution of bichloride of platinum 

 gives a crystalline yellow precipitate, which is a 

 double salt of bichloride of platinum and chloride 

 of potassium. If not previously acid, the mixture 

 to be tested should be acidulated with hydrochloric 

 acid. (3) The violet tint occurring in the presence 

 of potassium in the outer flame of the blowpipe, 



