20 MINERALS AND GEOLOGY 



ing in the monosyllable " ous " as sulphurous acid, arsenious acid, 

 &c. ; whilst the monosyllable " ic " terminates the generic name of 

 the more highly oxidized compound, as sulphuric acid, arsenic acid, 

 &c. As regards minerals or natural inorganic substances, "ous" 

 acids are all but unknown. The more common acids of the Mineral 

 Kingdom some of which occur both in the free state and in com- 

 bination with bases, others in the latter condition only comprise 

 Silicic acid, (conventionally known as Silica), Carbonic acid, Sul- 

 phuric acid, Phosphoric acid, Arsenic acid, &c. These acids have a 

 great tendency to combine with bases. The generic name of the 

 compounds which thus result, terminates in either the syllable tie or 

 ate. Ous acids give ite compounds with bases, and ic acids give ate 

 compounds. Except in a few rare instances the latter only are met 

 with among natural bodies. Silicic acid, in combining with a base 

 or with several bases, produces a silicate ; carbonic acid, in like man- 

 ner, produces a carbonate ; sulphuric acid, a sulphate ; arsenic acid, 

 an arseniate, and so forth. Many of these compounds yield water 

 when ignited : they are then known as hydrous or hydrated silicates, 

 sulphates, &c. 



In these oxidized compounds, it will be observed, three elements 

 are present. Thus, the mineral cyanite <a silicate,) contains alumi- 

 nium, silicon and oxygen ; and carbonate of iron contains iron, car- 

 bon and oxygen. If these minerals be chemically decomposed, they 

 separate into an oxidized base on the one hand, and into an oxidized 

 acid on the other. In other words, the silicate cyanite yields alumina, 

 or oxide of aluminium, and anhydrous silicic acid ; whilst from car- 

 bonate of iron, oxide of iron and carbonic acid are obtained. Calcite 

 or calcareous spar, in like manner, may be formed from, and decom- 

 posed into, lime or oxide of calcium and carbonic acid. If the 

 mineral be exposed to a red heat, carbonic acid is expelled in the form 

 of an invisible gas, and lime remains behind ; and if this lime be ex- 

 posed to the atmosphere it will gradually absorb carbonic acid from 

 the latter, and the original compound will again result. ^ 



Action of Acids. As a general rule, the use of acids may be dis- 

 pensed with in the ordinary determination of minerals, or resorted to 

 only as a confirmatory test, when the name of the substance has been 

 ascertained by other means. A drop of acid serves, however, very con- 

 veniently, to distinguish carbonates from most other bodies, by the 



