26. _Carbonic Acid_ is a compound of oxygen (21) and carbon, or pure charcoal (48): and in a state of gas (20) it forms a constituent part of the atmospheric air. It is also emitted in great abundance from wine, beer, and other liquors, in a state of fermentation, and is sometimes found in the lowest parts of mines, where it is known to the miners by the name of _choke damp_, from the circumstance of its immediately extinguishing flame, and suffocating all animals that are immersed in it. This gas, which was formerly called by chemists _fixed air_, is about twice the weight of common air. In combination with lime it forms chalk, marble, and limestone; and it constitutes part of several other mineral substances, which are thence denominated _carbonats_. 27. _Fluoric Acid_ is a gas of very singular nature, which is held in combination with lime, in the Derbyshire or fluor spar (194); and may be separated from it by pouring sulphuric acid, or spirit of vitriol (24), upon powdered spar, in a leaden vessel called a retort, and applying to it a gentle heat. The salts formed by fluoric acid have the name of _fluats_. 28. The _Boracic_ is a peculiar kind of acid, which, in combination with soda (200), forms the substance that we import from the East Indies under the name of borax (204). When extracted from borax this acid does not assume the form of a fluid, but appears in thin six─sided scales or flakes, of white colour, which adhere slightly together, and feel somewhat greasy in handling. To the taste it is at first sour, then bitterish; and at last it leaves an agreeable sweetness on the palate. 29. _Muriatic Acid_ is a gas formed by the combination of oxygen (21) with some base that is not yet known. It is an invisible and elastic fluid, which, in mechanical properties, resembles common air, and has a pungent and very peculiar smell. This gas unites with alkalies (42), earths (31), and the oxides (21) of metals; and with them forms the compounds called _muriats_, of which common salt, or muriat of soda (202), is one of the principal. The liquid muriatic acid, or muriatic acid gas combined with water, is frequently denominated _spirit of salt_ (202).