in liberating Gas from Solution. 303 



dyspepsia and other accidents. Hence two observers may draw 

 entirely different inferences from the same fact, and both be 

 equally wrong when the case comes to be referred to nature's 

 high court of appeal. 



When a scientific man says, " In the year 18 — I established 

 this fact/' he is within philosophical bounds, supposing the 

 fact to be such as can be repeated and verified by persons 

 capable of performing an experiment with accuracy. But when 

 he says, "In the year 18 — I established this explanation/' he 

 becomes non-scientific, because he confuses that which admits of 

 proof with that which can only be a matter of inference. 



If, for example, I pour into a test-glass a quantity of soda- 

 water and observe that numerous bubbles of gas cling to the 

 side, and then pour soda-water into another test-glass that has 

 just been made chemically clean, and find that no bubbles 

 adhere to the side, I infer that chemical cleanliness in the latter 

 case, and the absence of it in the former, are concerned in the 

 phenomena. If a line be drawn within the clean glass by 

 means of a glass rod smeared with grease or oil, such line 

 becomes instantly covered with gas-bubbles. In such case it 

 is fair to infer that a portion of the chemically clean surface is 

 thus made unclean, and that the different behaviour of the 

 gaseous solution depends on the distinction between chemically 

 clean and chemically unclean. 



But M. Gernez has recently informed us* that in 1866 he 

 established the conclusion that no gas is liberated below the 

 surface of a supersaturated gaseous solution, such as Seltzer 

 water, unless we introduce some kind of gaseous atmosphere, 

 such as that which is retained on the surface of a solid body or 

 in the capillary cavities of a porous body, and that it is into 

 this atmosphere that the gas held in solution expands and 

 escapes. 



In 1867 I published in this Magazine f an account of a 

 number of experiments in opposition to the view of M. Gernez, 

 the object of which was to show that while a gaseous super- 

 saturated solution, with its upper surface exposed to the air, 

 gives off gas, either with effervescence or imperceptibly, the 

 surface of the liquid confined by the sides of the vessel is subject 

 to two modifications — (1) The state of chemical purity of their 

 surface, and (2) the pressure exerted by them virtually on the 

 liquid. (1) If the vessel be chemically clean, no gas is disen- 

 gaged and no bubbles form on the sides, because the adhesion 



* Comptes Rendus, 4 Janvier 1875, p. 44. A translation of this Note 

 is given in the Phil. Mag. for February last. 



t "On the so-called 'Inactive' Condition of Solids," Phil. Mag. 

 August and September, 186/. 



