The saline combinations of strontia were examined with particular attention by Dr. Hope. See _Edinburg Philosoph. Transactions_ for 1790. Nitrate of strontia may be formed by dissolving carbonate of strontia, or the sulphuret obtained by decomposing the sulphate by charcoal, in nitric acid, filtering the solution, evaporating it, and suffering it to crystallize. Nitrate of strontia deflagrates on ignited coals. Dr. Hope pointed out, that if nitrate of strontia be exposed to a red heat, and a combustible substance be, at this time, brought in contact with it, a deflagration, with a very vivid red flame, will be produced. When a crystal of this salt is put into the wick of a candle, it communicates a beautiful purple flame. It does not deliquesce in the air, and, therefore, the compositions, into which it enters, cannot spoil on that account. Nicholson (_Chemical Dictionary_,) observes, that nitrate of strontia may be used in the art of pyrotechny. For this purpose, however, it is mixed with sulphur, chlorate of potassa, and sulphuret of antimony; and sometimes with the addition of sulphuret of arsenic and charcoal, as in the _red fire_ for theatrical uses. The muriate of strontia has similar properties. Davy first observed, that when strontia was heated in chlorine gas, it gave out oxygen gas, and a chloride of strontium was formed. Muriate of strontia is formed very readily, by dissolving the carbonate or sulphuret of strontia in muriatic acid, and evaporating the solution in order to obtain crystals. These crystals are very soluble in water. They are soluble, also, in twenty-four times their weight of pure alcohol, at the temperature of 60°. This alcoholic solution, we remarked, burns with a fine purple colour. These crystals suffer no change when exposed to the air, except they be very moist; in which case, they deliquesce. When heated, they first undergo the watery fusion, and are then reduced to a white powder. Fourcroy recommends the muriate of strontia for fire-works. Carbonate of strontia, when thrown in powder on burning coals, produces red sparks. Acetate of strontia, another salt used in fire-works, is formed by dissolving strontia, or its carbonate, in acetic acid. It will crystallize. The crystals are not affected by exposure to the air. When heated, its acid is decomposed, as happens to all the other acetates. _Sec. LIX. Of Boracic Acid._ Borate of soda, or borax, is a salt, which has long been known, and is used chiefly in the arts as a flux for the fusion of bodies, and for soldering. Boracic acid is a compound body, consisting of a newly discovered substance, called boron, and oxygen. Homberg obtained the acid from borax in 1702, by distilling a mixture of borax, and sulphate of iron. He supposed that it was a product of the latter; and hence it was called the _volatile narcotic salt of vitriol_, or _sedative salt_.