The sulphates, when heated to redness with charcoal, form sulphurets. When tested with solution barytes, they furnish copious precipitates.
433. Sulphate of soda, or Glauber's salt. This salt is chiefly prepared from that which remains in the retort after the distillation of muriatic acid. It will be remembered that muriatic acid is obtained by distilling a mixture of common salt and sulphuric acid. The latter acid combining with the soda of the salt, forms sulphate of soda, while the muriatic acid is set free. This new salt being dissolved in water and saturated with carbonate of soda, in case the acid predominates, forms the common Glauber's salt.
Obs. 1. This salt forms regular transparent crystals of a prismatic figure, terminated by pyramids truncated near their bases.
2. Its water of crystalization amounts to about half the weight of the salt.
3. It is strictly a neutral salt, as neither the alkali, nor acid predominates.
4. It is very soluble in water, three parts of which at 60 degrees dissolves one of the salt. It is composed of soda 46, and acid 54, to the 100.
Its use as a medicine, is well known.
434. Sulplwte of Barytes. This salt is found native, and is sometimes called baro-selinite, or heavy spar. It can also be formed by mixing the earth barytes with sulphuric acid. In the native state it is a white, or yellowish stone of a crystalline appearance, being composed of lamallar crystals, which when broken present plane shir ning faces. One of its most remarkable properties is its great weight, being heavier, bulk for bulk, than any other earthy substance.
435. Sulphate of barytes, when treated in a certain manner affords one of the solar phosphori.
Illus. The native sulphate being powdered and ignited, is sifted and mixed with mucilage of gum arabic. This is then divided into cylinders of one fourth of an inch in thickness. These after being dried in a moderate heat, are to be exposed to heatof a wind furnace, placed in the midst of the charcoal. When the fuel ig half consumed it must be replenished, and suffered to burn out. The cylinders will be found retaining their original shapes among the ashes. They must be preserved in a well stopped vial.
This phosphorus, after being exposed a few minutes to the sun's rays, shines in the dark sufficiently to render visible the dial of a watch.
436. Sulphate of barytes, artificially formed, is composed of about 66 barytes and 34 acid to the 100.
437- Sulphate of Lime is found native in great abundance, and is known under the names of plaster of pans, gypsum, Sic. It is chiefly employed as a manure. It is also used as a cement.
Obs. It contains about 21 per cent of water, which is easily evaporated when the salt is exposed to a low red heat. What remains,is an impalpable powder of a beautiful white. This powder is composed of lirne 58, add acid 42 = 100.
438. Sulphate of Magnesia, or Epsom salt. This salt is obtained by the evaporation of the water of some springs which contain it in solution. It is also found in sea water, and is sometimes prepared from what is called the bittern, which remains after the common salt is extracted. It is easily composed by mixing together its ingredients, sulphuric acid diluted with water and magnesia.
OAs. Sulphate of magnesia crystalizes in the form of small
exposed to the air; is very soluble in water and undergoes a watery fusion when exposed to heat. lis principle use is as a medicine. It is composed of water 50, acid 33.5 and magnesia 16.5 to the 100.