L. J. Wild 157 



removed lime from solution, that from Weka Pass gave it up to its 

 solution, the strength of which was increased from 0-019 N to 0-02 N. 

 To return now to the point that different hme requirements are 

 indicated for the same soil using solutions of differing strengths. The 

 authors of the method make no suggestions as to the nature of the 

 chemical action involved. As the soils of this farm give a strongly 

 acid reaction to litmus, we may take it for granted that the main 

 reaction is a simple one between the hme and the soil acids. Owing to 

 the excess of carbon dioxide, itself a competitor for the lime, we have 

 here a mass reaction ; it will take time to complete, but when completed 

 the result should be that the lime requirement indicated for any soil 

 should be the same irrespective of the concentration of the solution 

 employed, provided that the pressure in the system is kept constant. 

 An experiment was first inaugurated to find out how long a time is 

 necessary for the completion of the reaction. The soils used were from 

 a sample taken 6 in. deep from Field 21, and the times of exposure 

 increased successively by a period of 45 minutes. The initial strength 

 of the solution was -0216 N. The results are shown in the following 

 Table III. 



Table III. 



Percentage lime requirement indicated after 



, ^ — . . ^ 



Soil 45m. Ih.SOm. 2h. 15 m. 3h. 3h.45m. 4h. 30 m. 5h. 15m. 6h. 24h. 

 Field 21 -089 -131 -139 -146 -153 -153 -167 -160 -167 



These results confirm those obtained by Hutchinson and MacLennan 

 as showing that four hours is a sufficient length of time of exposure for 

 practical purposes. 



However to get clearer information as to the rate of progress of the 

 reaction, one further experiment was arranged. A large Winchester 

 was filled with 2400 c.c. of bicarbonate solution of strength -0241 N. 

 Into it was put 100 grams of soil from Field 21 ; the whole was shaken 

 up and portions of 100 c.c. were withdrawn and titrated at intervals of 

 5 minutes. The method is not entirely satisfactory, as owing to the 

 short exposure the portions were turbid and had to be filtered before 

 titration. The results are given below (Table IV). 



Table IV. 



Percentage lime requirement indicated after 



