86 Lime liitiiiirrnii'iils of ('ci-finii Soi/s 



changes procoeded still more ia])idly and resulted in fictitious values 

 being obtained. 



The capacity of the soil to absorb the base from neutral salts in 

 solution has formed the basis of a number of methods. Tn their earlier 

 worlc, Hopkins, Kno.x and Pettit (26) recommended that 100 giins. of 

 dry soil be digested in llic coliI for tliiec hours with 250 c.c. of a 5-0 per 

 cent, solution of sodium chloride, the whole being shaken at intervals. 

 At the end of this peiiod 125 c.c. of the clear supernatant litjuid was 

 syphoned oil' and. after being boiled for a few minutes to drive ofT carbon 

 dioxide, was titrated with standard alkali against phenolphthalein. 

 Actual experiment showed that displacement proceeded until an 

 equiUbrium was established and the removal of the liquid and successive 

 treatment of the same soil with fresh quantities of solution resulted in 

 values being obtained which were in the order of decreasing geometrical 

 progression. For routine work, however, it was found convenient to 

 employ a factor — the results of the titration of the first 125 c.c. ■ 3 

 giving results equal to those obtained by successive digestions. The 

 factor subsequently suggested was 4, while still later (27), where a normal 

 solution of potassium nitrate was employed, one of 2| was advised. 

 The earlier method has been criticised by Daikuhara (28), who was able 

 to show that the values given by sodium chloride were very much lower 

 than those obtained when other chiefly ammonium and potassium — 

 salts were used, and suggests that potassium chloride be employed. 

 Daikuhara's own work shows also tliat this salt gives values very similar 

 to those obtained with potassium nitrate, and he does not appear to 

 be aware that the latter salt had already been recommended bv Hopkins. 

 The factors given by Daikuhara are 3-5 and 3-0 for digestions of one and 

 five days respectively. Employing this method, he examined a very 

 large number of so-called ''acid mineral soils," such as appear to be 

 widely distributed tliroughout Japan and Korea, and the results present 

 several points of interest. One characteristic of the soils is that the 

 application of neutral mineral manures results in decreased crop yields, 

 whilst the zinc pots in which the e.xperiments were made were gradually 

 attacked and finally perforated. The soils fail to give an acid extract 

 with water and give a reaction with litmus paper only at the point of 

 contact with the soil. With neutral salt solutions an acid reaction is 

 produced immediately and this is advanced as a test for such acid soils. 

 It is important to note, however, that of 917 Japanese virgin soils. 738 

 gave a response to litmus paper and only 467 reacted to this test; the 

 method is not, therefore, generally applicable. 



