silica. 233 



chloride 3*7, magnesium sulphate 2 -30, calcium sulphate 

 1*4, calcium carbonate 0*03, with some magnesium bromide 

 and probably traces of iodides, fluorides, phosphates and 

 borates. The bitter taste of sea water is owing to the salts 

 of magnesium present. 



The waters of the Dead Sea contain 200 to 260 parts of 

 solid matter in 1,000 parts (or 20 to 26 per cent.), including 

 7 to 10 per cent, of common salt, the same proportion of 

 magnesian salts, principally the chloride, 2J to 3J per cent, 

 of calcium carbonate and sulphate, besides some bromides 

 and alumina. The density of these waters is owing to this 

 large proportion of saline ingredients. The brine springs 

 of New York and other States south and west, are well- 

 known sources of salt (see under Common salt). Many of 

 the springs afford bromine, and large quantities of it are 

 manufactured for making photographic plates and for other 

 purposes. 



Mineral waters vary much in constitution. They often 

 contain iron in the state of bicarbonate, like those of Sara- 

 toga and Ballstown, and are then called chalybeate waters, 

 from the ancient name for iron or steel, chalybs, derived ■ 

 from the name of a country on the Baltic. Hydrogen sul- 

 phide is often held in mineral waters and imparts to them 

 its odor and taste; such are the so-called sulphur springs. 



Minute traces of salts of zinc, arsenic, lead, copper, an- 

 timony and tin, have been found in some waters. What- 

 ever is soluble in a region through which waters flow, will 

 of course be taken up by them, and many ingredients are 

 soluble in minute proportions, which are usually described 

 as insoluble. 



III. SILICA AND SILICATES. 



I. SILICA. 



Quartz. 



Pthombohedral. Occurs usually in six-sided prisms, more 

 or less modified, terminated with six-sided pyramids : R/\R 

 = 94° 15'. No cleavage apparent, seldom even in traces ; 

 but sometimes obtained by heating the crystal and plunging 

 it into cold water. Sometimes in coarse radiated forms; 



