As strontia communicates a red colour to flame, it has been used in certain compositions of artificial fire. The brilliant red fire, sometimes used in theatres, owes its colour to this earth. See [Theatrical fire-works.] Muriate and nitrate of strontia will give a red or purple colour to the flame of alcohol. See [coloured flame of alcohol.]
If a piece of cloth be dipped in a solution of muriate, nitrate, or acetate of strontia, or in strontia water, and then immersed in alcohol, it will burn with a red flame.
M. Fourcroy, (Système des Connaissances Chimiques, &c. tome iii,) mentions the use of nitrate and muriate of strontia, in artificial fire-works, for the purpose of communicating a red colour to the flame of combustible bodies. Since that time, the nitrate, in particular, has been recommended and used.
One of the characters of the salts of strontia, is, that they give a red flame to burning bodies; whereas the salts of barytes or of lime, used in the same manner, communicate a yellow flame.
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.