Strontium Hydroxide, Sr(OH)₂

Strontium Hydroxide, Sr(OH)₂. - Strontium oxide may be "slaked" by water producing the hydroxide. The heat generated by this reaction is 19.44 Cal. Strontium hydroxide may be obtained as an intermediate product in the formation of strontium oxide from strontium minerals. It is prepared, for example, by the decomposition of strontium sulphide, or carbonate, by superheated steam at 500°-600° C., by the oxidation of the sulphide in a current of air in the presence of Wei don mud as catalyst, or by the action of sodium sulphate and carbon on the sulphide. It may also be formed in the dissolved state by the electrolysis of strontium chloride and sulphide solution with an iron or carbon anode.

The density of strontium hydroxide is 3.625.

By heating at 850° C. the oxide is again formed. In vacuo the greater part of the water is removed below 540° C., and dehydration is complete at 710° C.

The following values have been found for the vapour pressure of the hydroxide at different temperatures: -

Temperature, ° C.	452	488	524	561	597	634	670	706	742	778
Pressure in mm. Hg.	9.2	17.4	31.5	55	92	149	234	355	526	760

The heat of solution of strontium hydroxide is 19.43 Cal. It is more soluble than the calcium compound, and produces a strongly basic solution. The following values have been given for the solubility: -

Temperature, ° C	0	20	40	50	65	75	85	101.2
Grams SrO per 100 parts solution.	0.35	0.69	1.48	2.13	3.74	5.29	9.08	19.34

In the presence of bases the solubility is diminished to a greater extent than can be explained by the decrease of dissociation. The influence of strontium salts is very small, probably indicating the formation of compounds, basic salts, in solution. In solutions of strontium nitrate the solubility increases with the concentration of the latter, but no basic salts have been isolated. It is readily soluble in cane sugar solutions in which it forms strontium saccharate.

The molecular conductivities of strontium hydroxide solutions have been measured by Ostwald.

Under the influence of the cathode rays, strontium hydroxide gives a beautiful deep blue phosphorescence.

Strontium hydroxide octahydrate, Sr(OH)₂.8H₂O, separates as tetragonal crystals, of density 1.396, from solutions at ordinary temperatures. Berthelot ascribed to it the formula Sr(OH)₂.9H₂O. From vapour pressure measurements Lescoeur concluded that there was a higher hydrate than the octahydrate, and there also appear to be a hepta- and a di-hydrate. The heat of solution of the octahydrate is -14.27 Cal., and the heat of hydration from the hydroxide 24.60 Cal.

The monohydrate, Sr(OH)₂.H₂O, is formed by heating the octahydrate for two hours in a current of dry hydrogen at 45°-50° C., by leaving in vacuo over sulphuric acid, or by passing first air saturated with water vapour, and then dry air, at ordinary temperatures over strontium oxide. At 95° C. it loses its water of hydration, forming the simple hydroxide. The heat of solution of the monohydrate is 5.26 Cal., and the heat of hydration from the hydroxide 5.06 Cal. It absorbs carbon dioxide with complete transformation into the carbonate.

Strontium oxide forms compounds with mannitol.

The use of strontia in the sugar industry for the purification of sugar by the precipitation of di-strontium saccharate was first patented by Dubrunfaut and Leplay in 1849, and introduced into the German beet-sugar factories by Fleicher in 1869. The process was modified and improved by Scheibler.