The point of intersection of the curves of solubility lies at about 30° for the first two salts and about 45° for the salts with 4H₂O and 2H₂O. The crystals CaCl₂,2H₂O may, however, be obtained (Ditte) at the ordinary temperature from solutions 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 CaCl₂,H₂O 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 CaCl₂,4H₂Oβ, we will give the temperatures t at which the passage of one hydrate into another takes place and at which the solution CaCl₂ + nH₂O, 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: t n A B p -55° 14·5 ice CaCl₂,6H₂O 0 +29·8° 6·1 CaCl₂,6H₂O CaCl₂,4H₂O 6·8 45·3° 4·7 CaCl₂,4H₂O CaCl₂,2H₂O 11·8 175·5° 2·1 CaCl₂,2H₂O CaCl₂,H₂O 842 200° 1·8 CaCl₂,H₂O CaCl₂ Several atmospheres Solutions of calcium chloride may serve as a convenient example for the study of the 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 CaCl₂,6H₂O.

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 the crystallo-hydrate CaCl₂,6H₂O separates, and that a solution of the above composition (CaCl₂,14H₂O requires 44·0 parts calcium chloride per 100 of water) solidifies as a cryohydrate at about -55°.