CARBONIC ACID. 7'23 



The commercial value of the carbonates of potash and soda may equally well be deter- 

 mined by ascertaining the quantity of dilute sulphuric acid required to neutralise them. 



The following carbonates are such as find some use in the arts or being found 

 native, are brought under the notice of the miner : 



CARBONATE OF AMMONIA, COMMERCIAL. The sesquicarbonate of 

 chemists, sal volatile, or volatile or smelling salts of the shops. Bicarbonate of 

 ammonia has been found in considerable quantities, forming crystalline masses, in a 

 bed of guano on the western coast of Patagonia. 



CARBONATE OP BARYTA. This compound occurs in nature as the mineral 

 Witherite, which is found in lead mines. 



CARBONATE OF CALCIUM, or of LIME. Carbonate of lime is found abun- 

 dantly in the mineral kingdom. Calcareous spar, arragonite, Iceland spar, limestone, 

 chalk, and marble, are carbonates of lime. Its uses are well known. Gay-Lusslte is 

 a double carbonate of lime and soda. 



CARBONATE OF COBALT. See COBALT. 



CARBONATE OF COPPER. Malachite and azurite are the two carbonates 

 of this metal found in nature. See COPPER. 



CARBONATES OF IRON". Spathic ore is the most important native form 

 which occurs. See IROX. 



CARBONATE OF LEAD. White lead ore or cerussite is found in the load 

 mines of Cornwall, Devonshire, Cumberland, and Scotland. The pigment white lead is 

 a carbonate of lead. See LEAD. 



CARBONATE OF MAGNESIA. Magnesite occurs native, associated with ser- 

 pentine and other magnesian rocks. Magnesia alba of the pharmaceutists is a hydro- 

 carbonate. 



CARBONATE OF MANGANESE. This salt is found in nature in rose- 

 coloured rhombohedra known as manganese spar, or diallogite. 



CARBONATE OF NICKEL. A mineral called emerald nickel occurs at Texas, 

 in Pennsylvania, and at Unst, Shetland. This is the only native carbonate of this 

 metal. 



CARBONATE OF POTASH. Vegetable alkali, salts of tartar, pearl-ashes, 

 ashes, are several names given to this salt. See POTASH. 



CARBONATE OF SILVER. See SILVER ORES. 



CARBONATE OF SODA. Commonly called Soda. See SODA. 



CARBONATE OF STRONTIA. Occurs native as STRONTIANITK : it is found 

 at Strontian in Argyleshire hence its name ; in the Hartz and other localities. 



All these and the other rarer carbonates will be described under their respective heads. 



CARBONIC ACID. (Symbol, CO 2 ; Atomic weight, 22). The name commonly 

 applied to a compound of carbon and oxygen. This gas was formerly termed fixed air, 

 in consequence of its occurrence in a fixed form in chalk, marble, and other solid 

 carbonates, from which the gas may be readily released by the action of stronger acids, 

 conveniently by hydrochloric or muriatic acid. 



In modern chemistry carbonic acid gas is usually termed carbonic anhydride, the 

 name carbonic acid being restricted to the combination of the gas with water ; indeed, 

 the dry gas does not exhibit acid reactions, Carbonic acid gas is also known in 

 modern nomenclature as carbon dioxide. 



Carbonic acid is destitute of colour, has a sour smell, and an acidulous pungent 

 taste; it imparts to moist, but not dry, litmus-paper a transient reddish tint, and 

 weighs, per 100 cubic inches, 47'19 grains, and per cubic foot, 815*44 grains, or little more 

 than 3| oz. avoirdupois. It may be condensed into the liquid state by a pressure of 

 40 atmospheres; and this liquid may then be solidified by its own sudden spon- 

 taneous evaporation. If air contains 4 per cent, in bulk of this gas, it is rendered 

 unfit for respiration and combustion, animal life and burning bodies being speedily 

 extinguished by it. See Dr. Angus Smith's ' Air and Rain." 



Carbonic acid is constantly given off by animals during respiration ; and, ordi- 

 nary combustion consisting mainly in the combination of carbon with oxygen, this acid 

 is formed in enormous quantities in all our manufactories and by our ordinary fires. 



Carbonic acid is, consequently, continually being poured into the air. The purity of 

 the atmosphere is, however, maintained by the action of the vegetable world, all 

 plants removing carbonic acid from the air, and, under the influence of light, decom- 

 posing it again into carbon, which goes to the formation of wood and other vegetable 

 products, and oxygen, which is given out to the atmosphere. 



Notwithstanding this beautiful provision of Nature, we find carbonic acid accumu- 

 lating in caverns, deep wells, and long-closed cellars, rendering them dangerous. It 

 is the ' bad air ' and ' damp ' of the metal miner ; the ' choke damp,' ' after damp,' 

 and ' stythe ' of the coal miner. The last two terms are especially employed to express 

 the suffocating vapour which follows an explosion of ' fire-damp.' This gas, being 



3 A2 



