J. 4- Prkscott 



127 



G. Wiegiier has recently reviewed the whole subject^ and shown 

 that the absorption of ammonia by permutite (a technical calcium 

 aluminium silicate) from a solution of ammonium chloride follows the 

 absorption laws very completely; the equilibrium is instantaneous 

 when reached from above and the absorptive power is dependent largely 

 on the physical condition of the permutite. The CI ion is not absorbed. 

 The equilibrium attained was expressed by the formula 



~ = 3-429 C'«-398. 

 M 



The following table is worked out by Wiegner from the results of 

 various experiments and shows that the adsorption isotherm for soils 

 is of the usual type: 



In these experiments, the influence of temperature on the equilibrium 

 was only small but the absorption decreased with the rise of temperature, 

 as already shown by Schuhmacher. Equilibrium was very quickly 

 attained. Wiegner concludes that the fixation of bases by soils is 

 best explained as an adsorption phenomenon. 



The explanation usually put forward is that the substance actually 

 absorbed is the hydroxide. The OH can be replaced by other ions 

 such as the HCO3 but not usually by those of strong acids. The reaction 

 taking place between the soil and the neutral salt solution consists in 

 the estabhshment of an equilibrium between the various hydroxides and 

 since the acid radical is not absorbed to any appreciable extent some 

 of the hydroxides must be brought into solution. 



Lachs and Michaelis^ have shown that when charcoal is shaken with 

 alkali, much adsorption takes place — the OH ion being strongly absorbed. 

 If neutral salts are now brought into contact with the charcoal no 



1 Journ.f. Landw. 1912, 60, HI. 



- Zeitd. f. ElektrocJiem. 1911, 17, 1. 



