90 Ij'nni' Reqiilii'ini'iifx of (^crtniii Sollx 



For titiatioii ajjaiiist this .solution a scroiid one containing I7-(> 

 grnis. iodine and ^o-O f/ini.s. potassium iodide per litre was used. The 

 strength of the iodide solution is determined by taking 15 c.c. of the 

 " Kjeldahl's solution" together with 20 c.c. of N/5 hydrochloric or 

 sui[)liuric acid and titiating the excess of thiosulphate with tlii' iodine 

 solution, \\u\ difference between the value thus found and that of a direct 

 titration of the " Kjeldalds solution" being the one required. 



For the (leteirnination of acidity, 10 grins, of the fine soil (passing 

 thiough a I mm. sieve) are digested in a fiask with 15 c.c. of the " Kjel- 

 dahl's solution " for a prescribed period, after which the volume is made 

 up to 110 c.c. and 100 c.c. taken for titration. The results are chiefly 

 expressed as H ions per kilo of soil. The amount of reaction with the 

 soil depends, in the first place, on the concentration of the solution, 

 aiul the above strength is recommended ; it has further been found that 

 the change is not immcHliate but continues for a considerable period 

 with all soils, although where the soil is acid the greatest amount of 

 change takes place witiiin the hrst 24 hours. The slight additional 

 reaction l)etweeu this time and the end of 15 days is common to ail soils 

 and is doubtless due to interaction with inorganic soil constituents. It 

 must be noted that a positive leaction is given even when the soil 

 contains large amounts of carbonate and the setting of a limit of 

 maximum absorption for neutral soils appears desirable. 



A point brought out by the results of Gregoire and his co-workers 

 is that a fairly large proportion of soils occur that not only do not 

 jjossess any lime as carbonate but also fail to give any definite reaction 

 as to acidity; they are, in fact, just neutral and an estimation of 

 carbonate alone would fail to give ioli;il>le information as to tiie lime 

 re({iiii'ements of such soils. 



Exjtenmenlal. 



In the couise of our otiier work on the relative action of calcium 

 oxide iind carbonate on the soil, the need was felt of a simple and 

 accurate method for the determination of the lime re(j^uirenient»s of these 

 soils. In view of the fact that carbonates and bicarbonates are the 

 chief compounds tending to maintain a neutral reaction in the field, 

 and that any amelioration must proceed through this change, it 

 appeared likely that a closer investigation of the action of certain 

 carbonates on the soil might give a measure of prevailing acidity, and 

 would possibly conforiri more closely to natural conditions than some 



