BARYTES was discovered by Scheele in 1774 ; and the first account of its pro perties published by him in his Disserta tion on Manganese. This is a very heavy mineral, most frequently of a flesh colour, of a foliated texture, and brittle, very common in Britain and most other coun tries, especially in copper mines. It was known by the name of ponderous spar, and was supposed to be a compound of sulphuric acid and lime. Galin analyzed this mineral in 1775, and found that it is composed of sulphuric acid, and the new earth discovered by Scheele. Scheele published an account of the method of obtaining this earth from ponderous spar. The experiments of these chemists were confirmed by Bergman, who gave the earth the name of terra ponderosa. Mar veau gave it the name of barote, and Kir wan of barytes ; which last was approved by Bergman, and is now universally adopt ed. Barytes may be obtained in a state of purity, by the calcination of its carbo nate or nitrate. It exhibits, when pure, the following properties : 1. Barytes, in a pure form, has a sharp caustic taste, changes vegetable blue colours to green, and serves as the intermedium between oil and water : in these respects it bears a strong resemblance to alkalies. 2. When exposed, to the flame of the blow-pipe on charcoal, it melts, boils violently, and forms small globules, which sink into the charcoal. If perfectly free from wa ter, however, it is infusible. 3. If a small quantity of water be added to recently prepared barytes, it is absorbed with great rapidity ; prodigious heat is excit ed ; and the water is completely solidifi ed, a sort of hard cement being obtained. A little more water converts this mass into a light bulky powder ; and when completely covered with water, the ba rytes is dissolved. Boiling water shouldbe
employed for this purpose, unless suffi cient temperature has been produced by the sudden addition of the whole quan tity necessary for solution. 4. When the solution, prepared with boiling water, is allowed to cool slowly, it shoots into re gular crystals. These have the form of flattened hexagonal prisms, having two broad sides, with two intervening narrow ones; and terminated at each end by a quadrangular pyramid. 5. The crystals are so soluble as to he taken up when heated, merely by their own water of crystallization. When exposed to a strong er heat, they swell, foam, and leave a dry white powder, amounting to about 47 parts from 100 of the crystals. This again combines with water with great heat and violence. At 60° of Fahrenheit, an ounce measure of water dissolves only 25 grains of the crystals, i. e. they require for solu tion 17i times their weight of water. Exposed to the atmosphere, they efflo resce, and become pulverulent. 6.When added to spirit of wine, and heated in a spoon over a lamp, they communicate a yellowish colour to its flame. 7. The spe cific gravity of this earth, according to Fourcroy. is 4, but Hassenfratz states it at only 2.374. The former account, how ever, is the more probable. All its com binations have considerable specific gra vity; and hence its name is derived, viz. from the Greek word puetg, signifying heavy. 8. Barytes does not unite with any of the alkalies.