38 PHYSIOGRAPHY, CLASS I. 



dry atmosphere, and decrepitates upon glowing charcoal, or 

 before the blowpipe. It crystallises, both from solutions in 

 water, and from fusion. It undergoes a remarkable change if 

 exposed to a moist atmosphere, from which it attracts a por- 

 tion of water. The dissolution of a mass of a hexahedral 

 shape begins regularly at its edges, and transforms this first 

 into a combination of the hexahedron and the hexahedral 

 trigonal-icositetrahedron, Fig. 152., and then into a simple 

 form of that kind, without any additional faces, Vol. I. Fig. 

 32. In the latter form, the mass of the salt diminishes in 

 size, till at last it is entirely dissolved. 



3. The hexahedral Rock-salt occurs chiefly in beds, 

 some of which are of considerable dimensions, though 

 commonly of a rather irregular form, and is met with in 

 secondary, according to some geologists also in transition 

 rocks, accompanied by both the species of Gypsum-haloide, 

 principally the prismatoidal one, by several compound va- 

 rieties of rhombohedral Lime-haloide, associated with sand- 

 stone, clay, &c. It is likewise found at the bottom, and in 

 the vicinity of salt lakes, in the waters of which it is dis- 

 solved. It is contained in the waters of salt springs, of 

 several mineral wells, and of the sea, though in variable 

 quantities. It occurs upon certain varieties of lava, and in 

 some volcanic lakes. 



4. Hexahedral Rock-salt is found in considerable quan- 

 tity in Poland, Hungary, Transylvania, Moldavia, and 

 Valachia, in Stiria, Upper Austria, Salzburg, the Tyrol, 

 Bavaria, Wurtemberg, and Switzerland ; also in England, 

 in Spain, and in many other countries in and out of Eu- 

 rope. In several of these, and in some others, where this 

 salt has never been found in a solid state, there occur 

 nevertheless a number of salt-springs, from which it may 

 be obtained by means ef evaporation. The sea-salt in par- 

 ticular is found in the Crimea, in the deserts at the Cas- 

 pian Sea, in Egypt, and in several places in Southern Afri- 

 ca and America. 



5. The employment of hexahedral Rock-salt for culinary 

 purposes, in different arts and manufactures, &c. is too 



