Wild and Anderson. — Absorption of Lime by Soils. 



473 



given in the last column of Table VI were calculated, and here with one 

 exception excellent agreement is obtained, the mean value being 0-49. 



— — i ■ — i ^r \ 



4 ^ 



2 . / I . 



/~ I ' 



/■ - J— 



' I . \-5 I / 1 ]l-5 



Concentration Ca.0 Gms per Utre 



Fig. 2. 



6 | | 



— i^ 



2_y_ 



■5 



Final Concentration Cms per Utre 



Fig. 3. 



The equation for the parabola may now be compared with that for col- 

 loidal adsorption. 



The general formula representing colloidal adsorption is — 



m 



= kc tl 



where the symbols have the significance given above (p. 471). 

 may be transformed as follows : — 



By squaring JL _ ^2 c t, 



m- 



let n = 2 (see observation below) ; 

 then K = -- k 2 c, 



therefore 



Now, this 



m 



y2 — m 2 k 2 c, analogous to 



«2 = 4aa;the equation for the parabola. 



Therefore we may equate 

 m 2&2 __ ^ a . 



but m = 10, 



therefore k 2 = T ^o ^°^ 



therefore k = T \ V4a 



= t'o V-49 



= -07 

 1?ot this particular soil, therefore, the connection between the absorp- 

 tion of Ca(OH) 2 and the equilibrium concentration may be expressed — 



1 = -07 ci 

 m 

 Observation : The selection of the value n = 2 is more or less arbitrary, 

 and on it, of course, the value of k depends. It is well known, however, 

 that in the case of colloids adsorption varies with the valency of the ion 

 that is being adsorbed. Calcium functions as a dyad ; and for that reason, 

 as well as for the consequent conformity with the general parabolic equation 

 which the experimental curve seems to postulate, 2 has been adopted provi- 

 sionally as the value of this constant. 



