MINFRALOOY. 7 



ried into them daily by the fresh water streams. All lakes 

 without an outlet, including the Caspian Sea, have become 

 salty by this means. Soda, being one of the alkalies, has the 

 faculty of combining, under great heat, with silica and some 

 other refractory substances and causing their fusion. Thus a 

 mixture of powdered silica or quartz, with soda, when sub- 

 jected to great heat, forms glass. Soda is also employed, 

 when combined with fat, in the manufacture of soap. 



Potash is also one of the components of the most common 

 minerals and also of plants. It is, therefore, one of the most 

 important substances included in artificial fertilizers. 



Carbon is one of the few elements that are found in the 

 free state. The mineral graphite, or plumbago, consists of 

 carbon combined with a small quantity of iron, about one or 

 two per cent. In its purest condition carbon forms the min- 

 eral diamond, the hardest of all known substances ; while 

 graphite, consisting almost exclusively of carbon, is one of 

 the softest of min-erals. In the same category it may be 

 brought to mind that while mineral coal and charcoal are 

 common articles for fuel, graphite, practicall)' of the same 

 composition, is both incombustible and infusible. These are 

 two of the anomalous cases often encountered in scientific 

 pursuits, where the same substances, under varied conditions, 

 manifest great diversity in character. 



Combined with oxygen, carbon forms carbonic acid gas. 

 All limestones, including marbles, and all corals, shells and 

 chalk, consist of lime combined with carbonic acid. When 

 combined with sulphuric acid, lime forms the mineral g>^psum, 

 which in its purest condition is transparent, and it often 

 occurs in beautiful crystals called selenite. Alabaster is a 

 variety of gypsum. 



Next to aluminum iron is the most abundant of the metals. 

 It is one of the most common of the constituents of the min- 

 erals occurring everywhere. 



With one exception the ores of iron consist of that metal 

 c'ombined with oxygen in greater or less proportion under the 



