POTASSIUM, KttBIDIUM, CL&SIUM, AND LITHIUM 54JT 



KMgCl 3 ,6H 2 0, occurs at Stassfurt. This carnallite 2 is now em- 

 ployed as a material for the extraction of potassium chloride, and of all 

 the compounds of this element. 3 Besides which, potassium chloride 

 itself is sometimes found at Stassfurt as sylvine. 3bia By a method of 



9 Carnallite belongs to the number of double salts which are directly decomposed by 

 water, and it only crystallises from solutions which contain an excess of magnesium 

 chloride. It may be prepared artificially by mixing strong solutions of potassium and 

 magnesium chlorides, when colourless crystals of sp.. gr. T60 separate, whilst the Stass- 

 furt salt is usually of a reddish tint, owing to traces of iron. At the ordinary temperature 

 sixty-five parts of carnallite are soluble in one hundred parts of water in the presence of 

 an excess of the salt. It deliquesces in the air, forming a solution of magnesium chloride 

 and leaving potassium chloride. The quantity of carnallite produced at Stassfurt is now 

 as much as 100,000 tons a year. 



3 The method of separating sodium chloride from potassium chloride has been do- 

 scribed in Chapter I. On .evaporation of a mixture of the saturated solutions, sodium 

 chloride separates'; and then, on cooling, potassium, chloride separates, owing to the 

 difference of rate of variation of their solubilities with the temperature. The following 

 are the most trustworthy figures for the solubility of potassium chloride in oae hundred 

 parts of water (for sodium chloride, see Chapter X., Note 18) h 



10 20 40 60 100 



82 85 40 46 57 



When mixed with solutions of other salts the solubility of potassium chloride*, naturally 

 varies, but not to any great extent. 



5bt The specific gravity of the solid salt is 1'99 that is, less than that : of sodium 

 chloride. All the salts of sodium are specifically heavier than the corresponding salts of 

 potassium, as are also their solutions for equal percentage 'compositions. If the specific 

 gravity of water at 4 = 10,000, then at 15 the specific gravity of a solution of p p.o. 

 potassium chloride =9 ) Q92 + 68'29jp+0'2262? 8 , and therefore for 10 p.c> = r0647, 20 p.c. 

 *. 1-1348, &c. 



Potassium chloride combines with iodine trichloride to form a compound KCl-flClj 

 e= KICl^, which has a yellow colour, is fusible, loses iodine trichloride at a red heat, 

 and gives potassium iodate and hydrochloric acid with water. It is not only formed by 

 direct combination, but also by many other methods } for instance, by passing chlorine 

 into a solution of potassium iodide so long as the gas is absorbed, KI + 2C12=KC1,IC1 3 , 

 totassium iodide", when treated with potassium: chlorate and strong hydrochloric acid, 

 also gives this compound ; another method for" its formation ift given by the equation 

 KClO 3 +I + 6HCl=KCl,ICl 5 *3Cl+8I:LjO This is a kind of salt corresponding with 

 KIO Z (unknown) in which the oxygen -|s replaced! by chlorine. If valency be taken as, 

 the starting-point in the. study of chemical compounds, and the elements considered as 

 having a constant atomicity (number of bonds) that is, if K, Cl, and I be taken as 

 univalent elements then it is impossible to explain the formation of such a compound 

 because, according to this view, univalent elements are only able to form dual com- 

 pounds with .each other ; such as, KC1, C1I, KI, &o., whilst here they are grouped 

 together in the molecule KIC1 4 . Wells, Wheeler, and Penfield (1892) obtained a large 

 number of such poly-haloid salts. They may all be divided into two large classes: 

 the tri-h'aloid and* the penta-haloid salts. They have been obtained not only for K 

 tut also for Eb and Cs, and partially also for Na and Li. The general method of their 

 formation consists in dissolving the ordinary halogen salt of -the metal in water, and 

 treating it with the requisite amount of free halogen. The poly-haloid -salt'separates 

 put after evaporating the solution at a more or less low temperature. In this, manner, 

 among the tri-haloid salts, may be obtained : KI 3 , KBr 2 I, KC1 2 I, and the corresponding 

 ealts of rubidium and caesium, for instance, CsI 3 , CsBrI 2 , CsBr a i; CsClBrI CsCl 2 I, 

 CsBr 3 , CsClBr 2 , CsCl 2 Bi-, and in general Mj where $ is a halogen. The* colour of the 



