102O] AGRIOULTURAL CHEMISTRY — AGROTECIINY. 7l3 



Acidity and acidimcti-y of soils. III, IV, II. (i. KNifiiir {Jour. Indus, and 

 Enyin. Clicni., 12 {I'.t.iO), Xo. G, pp. 55'J-'>(>.!).—C(n\{iumn}i tlie investigation pre- 

 viously notiHl (K. S. 11., 43, p. G12), two pjipers are presented. 



III. Comparison of mcthodst for dctcnniniiuj Unir rcquiremtnta of .wils with 

 hydrof/en electrode (pp. 539, r.GO).— In tliis study 15 samples of soils, tlie lime 

 rf(iuireMient» of which as determined by the Veitch, Hopkins, Ilutchinstm- 

 MacLennan, Maclntlre, and vacuum methods had been reported by Ames and 

 Schollenberger,* were used for H-ion concentration determinations according 

 to the method described in the previous pajier. using n/2 KCl solution con- 

 taining various predetermined amounts of lime. By interpolating the results 

 obtained as straight line functions to determine the amount of lime nece!^sary 

 to lower the H-ion concentration to 10"' with a 0.G9 volt potential, a compari«t)n 

 was made with the results reportetl by Ames and Sehollenberger. 



From a study of these data the authors conclude that the vacuum method 

 approaches nearer to the lime requirements as shown by the hydrogen electrode 

 than do any of the other methods, although the results are uniformly higher. 

 " It is quite evident that the above methods, with the possible exception of the 

 vacuum method, do not indicate the amount of lime necessary to completely 

 neutralize a soil, especially in (he presence of neutral salts, except for a limited 

 period." 



IV. Propnued method for determination of lime requirements of soils (pp. 

 •5G()-5G2). — In this pai)er certain disadvantages of the hydrogen electrode method 

 for the practical determination of the lime requirements of soils are pointed out. 

 and a method is proposed which is said to appi'oximate the results obtained 

 with the hydrogen electrode but to be much more rapid and less expensive. 



The proposed method is essentially a modification of Tacke's method pre- 

 viously noted (E. S. R., 9, p. 32). A weighed quantity of the soil (from 5 to 

 10 gm.) is mixed with an excess of precipitated calcium carbonate in a 125 ec. 

 F>lenmeyer flask. This is att;iched to a Parr apparatus. 25 cc. of normal salt 

 solution is added, and the mixture is boiled for a tixed period, after which the 

 carbon dioxid evolved is determined by Pettit's modification of the Parr method 

 (E. S. R., 16, p. 038). The method was found to give varying results, depending 

 upon the time of boiling. A 10-minute period is recommended, although the 

 reaction is probably not complete even at the end of that time. 



" It is quite evident that any of the propos-ed methods gives comparative 

 results only. The true lime hunger as it relates to cropping is after all tne 

 matter that we are most interested in determining, and this, it seems, with the 

 present state of our knowledge must be determined by field experiments." 



By subtracting the acidity values found in acid soils from those found In 

 the limed soils from con-esponding half plats, the residual reduction in acidity 

 due to previous applications e(|uivaient to 5,700 lbs. of calcium carbonate was 

 determined. 



"As an average of the refills from seven plats which afford data for this 

 measurement the reduction in acidity is 2,S04 lbs. by the Hopkins method, 

 2,674 by the vacuum method, and 2,388 by the hydrogen electrode, while the 

 Maclntire, Hutchinson, and modified Tacke methods show reductions of 1.243, 

 1,279, and 1,375 lbs., resjiectively. That any method will show a greater reduc- 

 tion in acidity tlian actually occurs and remains at the time of sampling seems 

 extremely doubtful. 



"As suggested above, the vacuum method appears to furnish the most trust- 

 worthy measure of the total lime requirement, and it also seems .>siife to assume 

 that the hydrogen electrode will give results in substantial agreement with the 



> Jour. Indus, and lOngiu. Chem., 8 (1916), pp. 243-246. 



