78 PRINCIPLES OF CHEMISTRY 



there dissolve 180 volumes of carbonic anhydride, 130 of nitrous oxide, 

 and 437 of sulphurous anhydride, for these are gases which are rather 

 easily liquefied. (2) The solubility of a gas is diminished by heating, 

 which is easy to understand from what has been said previously that 

 the elasticity of a gas becomes greater as it is further removed from a 

 liquid state. Thus 100 volumes of water at dissolve 2-5 volumes of 

 air, and at 20 only 1*7 volumes. For this reason cold water, when 

 brought into a warm room, parts with a portion of the gas dissolved in 

 it. 30 (3) The quantity of the gas dissolved varies directly with the pres- 

 sure. This rule is called the late of Henry and Dalton, and is applicable 

 to those gases which are little soluble in water. Therefore a gas is 

 separated from its solution in water in a vacuum, and water saturated 

 with a gas under great pressure parts with it if the pressure be dimi- 

 nished. Thus many mineral springs are saturated underground with 

 carbonic anhydride under the great pressure of the column of water 

 above them. On coming to the surface, the water of these springs 

 boils and foams in giving up the excess of dissolved gas. Sparkling 

 wines and aerated waters are saturated under pressure with the same 

 gas. They hold the gas so long as they are in a well-corked vessel. 

 When the cork is removed and the liquid comes in contact with air at 

 a less pressure, part of the gas, unable to remain in solution at a lesser 

 pressure, is separated as foam with the hissing sound familiar to all. 

 It must be remarked that the law of Henry and Dal ton belongs to the 

 class of approximate laws, like the laws of gases (Gay-Lussac's and 

 Mariotte's) and many others that is, it expresses only a portion of a 

 complex phenomenon, the limit towards which the phenomenon aims. 

 The matter is rendered complicated from the influence of the degree of 

 solubility and of affinity of the dissolved gas for water. Gases which 

 are little soluble for instance, hydrogen, oxygen, and nitrogen follow 

 the law of Henry and Dalton the most closely. Carbonic anhydride 

 exhibits a decided deviation from the law, as is seen from the determi- 

 nations of Wroblewski (1882). He showed that at a cubic centi- 

 metre of water absorbs 1 -8 cubic centimetres of 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, 



~ According to Bunsen, 100 volumes of water under a pressure of one atmosphere 

 absorb the following volumes of gas (measured at and 7(50 mm.) : 



123 456 7 89 10 



4-11 2-03 1-93 179-7 3'3 ISO'S 437'1 688-6 5'4 104960 

 10 3-25 1-61 1-93 118-5 2'6 92'0 358-G 513-8 4'4 81280 



20 2-84 1-40 1-93 90'1 2"3 67'0 290'5 362'2 3'5 65400 



I, oxygen ; 2, nitrogen : 3, hydrogen ; 4, carbonic anhydride ; 5, carbonic oxide; 6, nitrous oxide; 

 7, hydrogen sulphide ; 8, sulphurous anhydride ; 9. marsh gas ; 10, ammonia. 



