198 ACIDIFEROUS ALKALINE MINERALS. ing not only in crystalline form, but in superior specific grav ity and hardness ; in being more difficultly soluble in water, and in its taste being less intensely alkaline ; neither does it de liquesce as natron does, and it may be preserved for any length of time unchanged in a dry atmosphere. It occurs in the province of Sukena in Egypt, forming a thin stratum in muriate of soda ; also in Barbary, and in Maracaibo and Columbia in South America. Trona is its African, Urao its American name. SULPHATE OF SODA. Glauber Salt. Naturlisches Glaubersalz, W. Sourte Sulphate'e, H- Prismatic Glauber Salt, M. Kxantholose, Beudant. Vesuvius. Hililesheim. Contains Soda 35-0 33-4 Sulphuric acid 44-8 42-3 Water 20-2 Beudant. 18-8 Beudant. Sp. Gr. P47. Primary form an oblique rhombic prism of 99° 36' and 80° 24'. Sulphate of soda is found in efflorescences of a yellow or greyish- white colour, or in an earthy form, but is more commonly dis solved in certain mineral waters; translucent or opake; lustre vitreous on the fresh fracture, dull on the surface; extremely efflorescent, and falling spontaneously into powder. It is cool ing, bitter and saline to the taste, and is usually met with in the neighbourhood of rock-salt or brine springs. Before the blow pipe in the matrass it melts in its water of composition. Sulphate ofsodaisfound in the salt mines of Upper Austria, Hun gary, and Switzerland; near Madrid in efflorescences at the bottom of a ravine ; at Grenoble in France ; in the workings of old mines, and sometimes on old walls, in the same manner as nitre. It is an ingredient of the hot springs of Carlsbad, Eger, and Sedlitz in Bohemia. When purified of the iron with which it is usually tinged in the native state, or when prepared artificially, it is used in medicine under the name of Glaubers Salt. NITRATE OF SODA. •Zootinsalz, Breithaupt. Soude Nitratee, Neikcr. Consists of Soda 45-03 37-2 Nitric acid 54-97 62-8 Gmelin. Sp. Gr. 2-1. II. = 1-5—2-0. Primary form an obtuse rhomboid of about 106° and 74°; cleav age parallel to the faces of the primary. This salt appears oc-