54 PRINCIPLES OF GENERAL PHYSIOLOGY 



in the surface film. In the same work it is shown dynamically that surface 

 tension, will have a large effect in changing the degree of chemical combination 

 (pp. 2:U i^7). 



Christoff (1912, p. 456) finds that the less is the surface tension of a liquid, 

 the greater is the solubility of gases in the liquid. The values of the absorption 

 coefficients (volume of gas dissolved by unit volume of liquid) at of g 

 of interest to the physiologist are as follows : 



The values for water are those of Winkler ; for alcohol, those of Bunsen ; and 

 for ether, those of Christoff. 



The results obtained by Vernon (1907) are of interest here. He showed that oxygen 

 is 4'5 times more soluble in oil and fat than in water, while nitrogen is 5'3 times more soluble. 

 In a rough experiment which I made, it was found that carbon dioxide was rather more 

 soluble in thick paraffin oil than in water. These various facts serve to show the futility of 

 attempting to preserve solutions from the action of gases in the atmosphere by covering them 

 with oil or hydrocarbons. They are also of importance in the results of exposure of animals 

 to compressed air. 



When gases are taken up by charcoal, it is clear that a large amount of 

 compression must occur ; some observers hold that, in the case of certain gases, 

 there must be actual liquefaction. Heat must be evolved in this process, a fact 

 whose meaning will be apparent later. 



Some chemical reactions are accelerated at interfaces, others retarded. Thus, 

 Freundlich (1906, p. 85) found an acceleration of the following reactions on the 

 surface of charcoal : oxidation of formic, citric and mandelic acids, and of 

 glycerol, hydrolysis of chlorine, esterification of alcohol with organic acids, 

 decomposition of phenyl-thio-urea. Perman and Greaves (1908, p. 366) found 

 that the rate of decomposition of ozone by heat depends on the extent of surface 

 to which the gas is exposed and that in all probability the reaction takes place 

 only there. 



An interesting case of retardation of a reaction by surface forces is that called 

 by its discoverer, Liebreich (1886), the "dead space." This observer noticed that 

 if a molar solution of sodium carbonate be mixed with a half-molar solution of 

 chloral hydrate in a test tube, the turbidity, which gradually forms by the 

 production and separation of chloroform, is absent from the surface layer of the 

 fluid, and he was able to show that this clear space was really due to the reaction 

 not having taken place therein. This retardation can be accounted for, thermo- 

 dynamically, if the reaction resulted in an increase of surface energy, since all 

 processes which lead to an increase of free energy are opposed. It is interesting 

 to find, therefore, that it was found by Dr Monckman in the Cavendish Laboratory 

 at Cambridge, that the surface tension increased considerably as the reaction went 

 on (.1. J. Thomson, 1888, p. 237). This effect is, no doubt, due to the comparative 

 insolubility of chloroform and the disappearance of the chloral hydrate, from 

 which it is formed. 



ADSORPTION 



Any substance dissolved in water lowers th^surface tension at the interface 

 between the solution and a solid, or immiscible liquid. With the exception of 

 certain inorganic salts, this is also the case at the interface between the 

 solution and a gas. Further, at these interfaces there is a local accumulation 

 of free surface energy, which can be altered in amount by the deposition of 

 substances at the interface. It follows, then, from the second law of energetics, 



