22 THE ROYAL SOCIETY OF CANADA 



Method. 



The term Lime Requirement as used in this paper means the num- 

 ber of pounds of lime per acre required to neutralize the soil acidity. 



The Rothamstead method} A Ca(HC03)2 solution was made 

 as follows: An excess of CaCOs (20 g.) was placed in a 10 liter bottle 

 with 6 liters of distilled water and a stream of CO2 was passed through 

 the solution for 48 hours or more, the bottle being thoroughly shaken 

 from time to time. The solution was allowed to settle and was titrated 

 with O.lNHCl. 



To determine the lime requirement of a soil, 10 g. of the soil was 

 placed in a liter flask with 150 cc. of the Ca (HC03)2 solution and a 

 stream of CO2 was passed through to displace the air. The flask was 

 then closed with a rubber stopper and was shaken at intervals of 20 

 minutes for 3 hours. The solution was then filtered and titrated 

 with O.lN.HCl. The lime requirement in lb. per acre was calculated 

 on the basis that 1 cc. of O.lN.HCl neutralizes 5 mg. of CaCos and 

 that 1 acre of soil 6 in. deep weighs 2,000,000 lb. 



The Electrical Method. The steps in this method, made in du- 

 plicate, were as follows: — 



(1) Soil Solution. A 10 g. sample of each soil was placed in a 

 shaker bottle with 150 cc. of distilled water and shaken for 3 

 hours. The solution was then allowed to settle over night and 

 the electrical resistance, ri, (the reciprocal of the conduc- 

 tivity) was measured with a Kohlrausch bridge. 



(2) Fertilizer Solution. The resistance, r2, of the original Ca 

 (HC03)2 solution was measured in the same way. 



(3) Soil- Fertilizer Solution. The resistance was measured of the 

 solution formed (in the Rothamstead test) by shaking 10 g. 

 of soil with 150 cc. of Ca(HC03)2 solution. 



This is the observed resistance OR. 



(4) Calculated Resistance. If we let 



ri= the resistance of the soil solution. 

 Ci= the conductivity " " " 



0R= the observed resistance of the soil-fertilizer sol'n. 

 0C= the " conductivity " " " " " 



r= the calculated resistance of the Ca(HC03)2 solution, 

 that is, the resistance this solution must have, 

 after being shaken with the soil, in order to give the 

 observed resistance OR, assuming that the resistance 

 of the soil solution remains constant. 

 c= the corresponding conductivity. 



^Hutchison and MacLennan, Journal of Agricultural Science, Vol. VII., Part I, 

 March, 1915, p. 91. 



