604 PEINCIPLES OF CHEMISTRY 



As for potassium, K=39 (and sodium, Na = 23), there are the 

 near analogues, lib = 85 and Cs = 133, and also another, Li = 7, so 

 in exactly the same manner for calcium, Ca = 40 (and magnesium, 

 Mg = 24), there is another analogue of lighter atomic weight, or 

 beryllium, Be = 9, besides the near analogues, strontium, Sr = 87, and 

 barium, Ba=137. As rubidium and caesium are more rarely met 

 with in nature than potassium, so also strontium and barium are rarer 



culty than magnesium chloride and with greater ease than barium chloride (Kuhnheim). 

 Sodium does not decompose fused calcium chloride even with further heating (Lies- 

 Bodart), but an alloy of sodium with zinc, lead, or bismuth decomposes it, forming an 

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

 evolves 18723 calories, and in dissolving in alcohol 17555 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/3 are formed, which at temperatures above 38'4 are converted into the 

 crystallo-hydrates CaCl 2 ,2H 2 O, whilst at temperatures below 18 the variety j8 passes into 

 the more stable CaCl 2 ,4H 2 Oa, which process is aided by mechanical friction. Hence, as 

 is the case with magnesium sulphate (Note 27), one and the same crystallo-hydrate ap- 

 pears in two forms the #, which easily forms, but does not keep and is unstable, and the 

 other, a, 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) 



CaCl 2 ,4H 2 Oo 90 101 117, 



CaCl 2 ,4H 2 0)8 104 114 



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



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

 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. 



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

 deposit ice if they contain less than 48 parts of salt per 100 of water, and if more the 

 crystallo-hydrate CaCl 2 ,6H 2 O separates, and that a solution of the above composition 

 (CaCl 2 ,14H 2 O requires 44'0 parts calcium chloride per 100 of water) solidifies as a cryo- 

 hydrate at about 55. Thus the solubility of calcium chloride is better known than 

 that of any other salt. 



Neglecting the unstable equilibrium CaCl 2 ,4H 2 O)3, we will cite the temperatures t at 

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

 CaCl 2 + wH 2 O, the two solids A and B and aqueous vapour, whose tension is given ae p 



