GASES IN SOLUTIONS. 69 



therefore important factors in the action of ground waters, but they are of 

 course only a small portion of the substances which ground waters carry. 

 The more important of these gases which pass into ground waters are: 

 Oxygen (0 2 ), carbon dioxide (C0 2 ), hydrosulphuric acid (H 2 S), sulphur- 

 ous oxide (S0 2 ), hydrochloric acid (HC1), hydrofluoric acid (HF), boric 

 acid (H3BO3), and ammonia (NH 3 ). Sulphur and boric acid as gases occur 

 mainly in connection with volcanic action. If the above-mentioned or 

 other gases unite with the water the laws below given as to solubility do 

 not hold; thus carbon dioxide unites with water, forming carbonic acid 

 (C0 3 +HoOr:H 3 C03); sulphurous oxide unites with water, producing sul- 

 phurous acid (SOo + HoO — H0SO3); ammonia unites with water, producing 

 ammonium hydrate (NH 3 + H 3 0— NH 4 OH). In some of these cases, for 

 instance, that of ammonia and sulphurous oxide, the water may unite with 

 many times its volume of the gas, with increase of volume; thus water at 

 0° C. and atmospheric pressure absorbs 1,050 volumes of ammonia as a 

 result of the union of the two. What portion of C0 2 contained in ground 

 water remains as C0 2 in solution, and what part unites with water, forming 

 carbonic acid, is uncertain, but it is definitely known that much of the C0 2 

 contained in the ground water is in the form of the so-called bicarbonates — 

 for instance, such salts as Na 2 C0 3 -f-H 2 C0 3 or 2NaHC0 3 — and therefore is 

 united with the water. 



When new compounds are formed by the union of the gases with the 

 liquids, the substances held in solution are the new compounds. When 

 these new compounds are gases the laws below given concerning the solu- 

 tion of gases in liquids apply only to the new compound, not to the original 

 gas. Where the compound is a solid — as, for instance, a bicarbonate — the 

 laws for the solution of gases in water do not apply, but such compounds 

 are held under the laws controlling the solution of solids in liquids. (See 

 pp. 72-82.) 



In some cases in nature a part of a gas may unite with a substance in 

 solution and make a new compound and a part may unite with water and 

 be dissolved in this form. If both the compounds be gases the laws for the 

 solution of gases in liquids hold. If the new compound formed be a solid 

 salt the laws for the solution of solids in liquids apply to it, and the laws 

 for the solution of gases in liquids apply to the uncombined gas. This case 

 is illustrated by carbon dioxide, already mentioned. 



