Jan. is, 1921 Concentration of Potassium in Orthoclase Solutions 621 



down of the complex. We may also assume that the solute complex is 

 not dissociated, at least in such a way as to liberate potassium ions. 

 For we can say with some assurance that free potassium ions would be 

 absorbed by the wheat seedlings. We have evidence of this in the 

 selective absorption exercised by wheat seedlings on potassium-chlorid 



solutions in which the potassium (either as K KOFH * s se l ect ively 



absorbed to such an extent that the culture solution becomes distinctly 

 acid. 



The effect of the oxidation of the solute complex in orthoclase 

 solutions by hydrochloric and nitric acids is to reduce the potassium 

 in the complex to potassium chlorid or potassium nitrate (KN0 3 ), in 

 which form it dissociates and is readily absorbed. 



The evidence presented in the case of orthoclase leads to the general 

 statement that the concentration of a specific plant food element in the 

 soil solution does not necessarily provide any measure of its availability. 

 The question of availability must be referred to the plant itself, except 

 perhaps in those cases in which the element in question is known to be 

 ionized. 



The results of our experiments have an immediate bearing on various 

 investigations now in progress looking toward the utilization of ortho- 

 clase as a source of potash. It should be borne in mind that the appli- 

 cation of finely ground orthoclase, without other treatment, probably 

 does not contribute immediately to the available potash content of the 

 soil. 



CONCLUSIONS 



From the experimental data presented the following conclusions are 

 drawn, subject to the limitations imposed by the experimental error: 



(1) The soluble potassium in aqueous solutions derived from finely 

 ground orthoclase is not absorbed by wheat seedlings to a measurable 

 degree. 



(2) The availability of the potassium is not increased by the addition 

 of lime, gypsum, or carbon dioxid to the solutions or by boiling the 

 solutions. 



(3) The soluble potassium in orthoclase solutions is made available by 

 oxidizing the solute with hydrochloric and nitric acids. 



(4) The increase in the availability following oxidation is not due to 

 the action of the acids on suspended colloids, but is to be ascribed to 

 the breaking down of the complex solute molecule. 



(5) The concentration of a specific plant food element in the soil 

 solution does not necessarily provide any measure of its availability. 

 The question of availability must be referred to the plant itself. 



