156 Lime Requirements of NeiD Zealand Soils 



Another point, however, must be mentioned at this stage. In one 

 experiment a positive, though small, lime requirement was indicated 

 for a limestone-derived soil containing about 10 % of calcium carbonate, 

 and this suggested the possibility of a weakening of the solution (which 

 corresponds to a lime requirement) from physical as well as from chemical 

 causes. To test this idea, a series of trials was made. Four soil 

 samples that had already been in contact with bicarbonate solution for 

 24 hours in connection with previous trials,' and which were now pre- 

 sumably satisfied as regards their lime requirements, were filtered from 

 their first solution and treated again with fresh solution. A sample of 

 sand was prepared by treating alternately with concentrated HCl and 

 strong ammonia solution, washing thoroughly, and separating a uniform 

 sample by sedimentation. About 9 grams of this sand was treated in 

 the same way as the soil. Another bottle contained a soil derived from 

 limestone from Waikari ; and lastly a bottle of the bicarbonate solution 

 without any soil at all was put through the same processes as the others 

 of this series. The results are given in Table II, the first four soils 

 being samples which, having been previously treated, were presumably 

 already saturated. 



These results indicate that all soils remove a certain quantity of 

 lime from the bicarbonate solution independently of their actual lime 

 requirement, provided that the solution is above a certain concentration 

 initially!. The Weka Pass soil can scarcely be in a different chemical 

 condition as regards lime to that from Waikari, since both contain a 

 large excess of calcium carbonate; and yet whereas the Waikari soil 



1 This observation is confirmed by H. W. Maclntire. See American Journal of Indus- 

 trial and Engineering Chemistry, Vol. vii, No. 10 (1915), page 860. 



