THE VALENCY AND SPECIFIC HEAT OF THE METALS 613 



Just as for potassium, K = 39 (and sodium, Na 23), there are 

 the near analogues^ Rb = 85 and Cs = 1 33, and also another, Li = 7, so 



alloy of calcium with one of the above-named metals (Caron). The zinc alloy may be 

 obtained with as much as 15 p.c. of calcium Calcium chloride is soluble in alcohol and 

 absorbs ammonia. 



A gram molecular weight of calcium chloride in dissolving in an excess of water 

 evolves 18,723 calories, and in dissolving in alcohol 17,555 units of heat, according to 

 Pickering. 



Roozeboom made detailed researches on the crystallo-hydrates of calcium chloride 

 (1889), and found that CaCl 2 ,6H 2 O melts at 30-2, and is formed at low temperatures from 

 solutions containing not more than 103 parts of calcium chloride per 100 parts of water; 

 if the amount of salt (always to 100 parts of water) reaches 120 parts, then tabular 

 crystals of CaCl 2 ,4H 2 O/J are formed, which at temperatures above 88'4 are converted 

 into the crystallo-hydrates CaCl 2 ,2H 2 O, whilst at temperatures below 18 the /J variety 

 passes into the more stable CaCl 2 ,4HoOa, which process is aided by mechanical friction. 

 Hence, as is the case with magnesium sulphate (Note 27), one and the same crystallo* 

 hydrate appears in two forms the )3, which is easily produced but is unstable, and 

 the o, which is stable. The solubility of the above-mentioned hydrates of chloride 

 of calcium, or amount of calcium chloride per 100 parts of water, is as follows : 



20 30 40 60 



CaCl 2 ,6H 2 O 60 75 100 (102'8) 



ITT r_ on tnt i IT . 



(154-2) 



CaCl 2 ,4H 2 Oa - 90 101 117 



CaCl 2 ,4H 2 O0 104 114 



CaCl 2) 2H 2 O - (308-3) 128 137 



The amount of calcium chloride to 100 parts of water in the crystallo-hydrate is 

 given in brackets. The point of intersection of the curves of solubility lies at about 

 80 for the first two salts and about 45 for the salts with 4H 2 O and 2H 2 O. The crystals 

 CaCl 2 ,2H 2 O may, however, be obtained (Ditte) at the ordinary temperature from solu- 

 tions containing hydrochloric acid. The vapour tension of this crystallo-hydrate equals 

 the atmospheric at 165, and therefore the crystals may be dried in an atmosphere of 

 steam and obtained without a mother liquor, whose vapour tension is greater. This 

 crystallo-hydrate decomposes at about 175 into CaCl 2 ,H 2 O and a solution ; this is easily 

 brought about in a closed vessel when the pressure is greater than the atmosphere. 

 This crystallo-hydrate is destroyed at temperatures above 260, anhydrous calcium 

 chloride being formed. 



Neglecting the unstable modification CaCl 2 ,4H 2 O, we will give the temperatures t at 

 which the passage of one hydrate into another takes place and at which the solution 

 CaCl 2 -f H 2 O, the two solids A and B and aqueous vapour, whose tension is given as p 

 in millimetres, are able to exist together in stable equilibrium, according to Roozeboom's 

 determinations : 



Solutions of calcium chloride may serve as a convenient example for the study of thd 

 Supersaturated state, which in this case easily occurs, because different hydrates are 

 formed. Thus at 25 solutions containing more than 83 parts of anhydrous calcium 

 chloride per 100 of water will be supersaturated for the hydrate CaCl 2 ,6H 2 O. 



On the other hand, Hammerl showed that solutions of calcium chloride, when frozen, 

 deposit ice if they contain less than 43 parts of salt per 100 of water, and if more th$ 



