Calcion

Calcium forms only one kind of ion, viz. divalent calcion, Ca^••. The heat of formation of this from the metal is 458 kj. In using this number for the calculation of the heats of formation of dissolved calcium salts, it has to be noticed that the heats of formation of monovalent anions must be doubled in the calculation.

Solutions which contain calcion have no immediately conspicuous properties; thus, they are colourless when no other substance possessing a colour is present. Since there is a considerable number of difficultly soluble calcium salts, there is a correspondingly large number of substances by means of which precipitates can be produced in solutions containing calcion. For our purpose, two of these are especially important, viz. carbanion, CO₃'', and oxalanion, C₂O₄''. The latter, more especially, is a specific reagent for calcion; for it forms with it the very sparingly soluble calcium oxalate, which is deposited as a fine, white precipitate when the two kinds of ions come together in solution.

No " complex" ions are known in which calcium forms a part; wherever, therefore, calcium is present in aqueous solution, calcion is also present.