122 Phenomenon of Absorptioii in its Belation to Soils 



of amyl alcohol in water has a higher concentration of the alcohol than 

 the original solution ; amyl alcohol lowers the surface tension of water. 

 J. V. Zawidzki^ has obtained similar results with saponin. 



It is extremely probable that the surface liquid-solid also shows 

 surface tension phenomena, but so far no methods have been devised 

 for determining its magnitude; but the above reasoning is still 

 applied. The further discussion of the theoretical side of this subject 

 leads into the realms of molecular physics and lies outside the scope 

 of this paper. Negative absorption, i.e. the decrease in concentration 

 at the surface of the solid, was first observed by C. Matteucci^ 

 who found that the density of a solution of sodium carbonate was 

 increased by filtration through three metres of sand. G. Gore^ investi- 

 gated very fully the absorption of various salts by silica and obtained 

 13 cases of negative absorption, 97 cases with positive adsorption and 

 30 cases with no result. S. Lagergren* found negative adsorption in 

 the cases of sodium, potassium and ammonium chlorides and animal 

 charcoal. A. M. Williams^ found that the adsorption of potassium 

 chloride and magnesium sulphate by charcoal increases with the 

 concentration to a maximum, then decreases, then passes through 

 zero and finally becomes negative. 



F. T. Trouton® has shown that a similar maximum of adsorption 

 occurs at a definite concentration with certain sulphates and nitrates 

 in contact with silica. The adsorption is not much influenced by 

 small changes of temperature, but is diminished by a rise in temperature ; 

 below the critical concentration as given in the above experiments of 

 Trouton an increase of adsorption follows a rise of temperature. 



The adsorption isotherm. 



Generally speaking the adsorption increases with the concentration 

 of the solution according to a simple relationship which can be expressed : 



Y . \ 



^r^ = KC^\ where 1 = amount of substance adsorbed by M of adsorbents 



M J ^ 



C = concentration of solution in equilibrium with Y, 

 K and P are constants. 



1 Zeifs. phys. Chem. 1903, 42, 612. 



^ Sur les phenomenes physiques des corps vivants, 1847. 



3 Birmingham Phil. Soc. 1893, 9, 1; sec Chem. Neivs, 1894, 69, 22, 33, 43. 



" Bihang till K. Sv. Vet. Akad. Handl. 1898, 24, Afd. 11, No. 4. 



^ Trans. Faraday ^nc. 1914, 10, 1.5.5. 



« British Assn. Report, 1914; Nature, 1914, 93, 642. 



