the gas under a pressure of one atmosphere; under 10 atmospheres, 16 cubic centimetres (and not 18, as it should be according to the law); under 20 atmospheres, 26·6 cubic centimetres (instead of 36), and under 30 atmospheres, 33·7 cubic centimetres.[31] However, as the researches of Sechenoff show, the absorption of carbonic anhydride within certain limits of change of pressure, and at the ordinary temperature, by water--and even by solutions of salts which are not chemically changed by it, or do not form compounds with it--very closely follows the law of Henry and Dalton, so that the chemical bond between this gas and water is so feeble that the breaking up of the solution with separation of the gas is accomplished by a decrease of pressure alone.[32] The case is different if a considerable affinity exists between the dissolved gas and water. Then it might even be expected that the gas would not be entirely separated from water in a vacuum, as should be the case with gases according to the law of Henry and Dalton. Such gases--and, in general, all those which are very soluble--exhibit a distinct deviation from the law of Henry and Dalton. As examples, ammonia and hydrochloric acid gas may be taken. The former is separated by boiling and decrease of pressure, while the latter is not, but they both deviate distinctly from the law. +---------------+-----------------+--------------------+ |Pressure in mm.|Ammonia dissolved| Hydrochloric acid | | of mercury | in 100 grams of |gas dissolved in 100| | | water at 0° |grams of water at 0°| +---------------+-----------------+--------------------+ | | Grams | Grams | | 100 | 28·0 | 65·7 | | 500 | 69·2 | 78·2 | | 1,000 | 112·6 | 85·6 | | 1,500 | 165·6 | -- | +---------------+-----------------+--------------------+