Calcium chloride has a specific gravity 2·20, or, when fused, 2·12, and the sp. gr. of the crystallised salt CaCl2,6H2O is 1·69. If the volume of the crystals at 0° = 1, then at 29° it is 1·020, and the volume of the fused mass at the same temperature is 1·118 (Kopp) (specific gravity of solutions, see Note 855). The solution containing 50 p.c. CaCl2 boils at 130°, 70 p.c. at 158°. Superheated steam decomposes calcium chloride with more difficulty than magnesium chloride and with greater ease than barium chloride (Kuhnheim). Sodium does not decompose fused calcium chloride even on prolonged heating (Liés-Bodart), but an alloy of sodium with zinc, lead, and 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 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 CaCl2,6H2O 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 CaCl2,4H2Oβ are formed, which at temperatures above 38·4° are converted into the crystallo-hydrates CaCl2,2H2O, whilst at temperatures below 18° the β variety passes into the more stable CaCl2,4H2Oα, which process is aided by mechanical friction. Hence, as is the case with magnesium sulphate (Note 855), one and the same crystallo-hydrate appears in two forms—the β, which is easily produced but is unstable, and the α, 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:— 0° 20° 30° 40° 60° CaCl2,6H2O 60 75 100 (102·8) CaCl2,4H2Oα — 90 101 117 (154·2) CaCl2,4H2Oβ — 104 114 — CaCl2,2H2O — — (308·3) 128 137 The amount of calcium chloride to 100 parts of water in the crystallo-hydrate is given in brackets.