STRONTIUM, a metallic chemical element intermediate in its character between barium and calcium, with which it forms a natural “triad.” Though widely diffused as a frequent companion of calcium (including oceanic), it occurs nowhere in abundance. Its most important mineral forms are the sulphate, SrSO 4 , known as Coelestine (from the sky-blue colour of certain varieties), and the carbonate, SrCO 3 , called Strontianite because it was discovered first at Strontian, in Argyllshire, Scotland. Crawford and (independently of him) Cruickshanks in 1790 were the first to recognize the latter mineral as a thing of its own kind and different from witherite (BaCO 3 ). Hope, in 1793, proved it to be the carbonate of a new earth, which discovery was confirmed by Klaproth.

Regarding metallic strontium, see Chemistry, vol. v. pp. 525-6. For the making of strontium preparations strontianite, of course, is the handier raw material, being readily convertible into (for instance) nitrate by treatment with dilute nitric acid. From the nitrate the oxide, SrO, is obtained by prolonged calcination at ultimately a bright red heat, as a greyish-whifce absolutely infusible and non-volatile mass, which acts violently on water with formation of the hydrate, Sr(OH) 2 , which latter readily takes up 8H 2 O of water to form crystals soluble in fifty parts of cold and far less of boiling water. An impure oxide is obtainable directly from strontianite by strong ignition with charcoal; and from such crude oxide pure crystals of the hydrate are easily produced by obvious operations.

In the working up of coelestine the first step is to reduce it to sulphide, SrS, by means of charcoal at a red heat. The sulphide when boiled with water is decomposed thus :—

2SrS + 2H 2 O = SrOH 2 O + SrSH 2 S....