MAR. 19, 1923 WHERRY: ACIDITY AND LIME-REQUIREMENT OF SOILS 99 
found to be, as would be expected, quite negligible (about lime-require- 
ment 0.002). The conclusion seems necessary, therefore, that the 
bulk of the lime taken up by a soil goes to neutralize hydrogen-ion 
adsorbed on the colloids; or, in other words, the lime requirement is 
essentially a measure of the amount of adsorbed hydrogen-ion present 
in a given soil. 
The ratio between adsorbed hydrogen-ion (lime-requirement) and 
soluble hydrogen-ion (specific acidity) accordingly depends on the 
quantity and character of the colloid matter present. If several 
soils contain approximately the same amount of essentially identical 
kinds of colloid, then this ratio should be the same for all of them; a 
correlation between specific acidity and lime-requirement could be 
said to exist, and, provided the ratio has been determined in one 
instance, the lime-requirement could be calculated from observed 
values of specific acidity for this whole series of soils. 
Data on gravelly loam soils.—All four soils discussed by Blair and 
Prince in the paper cited were considered to belong to the same soil 
type, Sassafras gravelly loam. To ascertain whether the ratio between 
specific acidity and lime-requirement is the same for all of them, these 
two quantities should be compared with one another directly. To this 
end, specific acidity values have been calculated from the Ps by the 
procedure above given, and lime-requirement values in tons have 
been obtained by dividing the number of pounds of CaO by 2000. 
The ratio between these two values may be simply and conveniently 
expressed in the form of a correlation coefficient, appropriately desig- 
nated by the initial letter of the word colloid, C; this is the factor by 
which specific acidity (S.A.) must be multiplied to obtain lime-require- 
ment (L.R.), that is, L.R. = C x (8.A. — 1). In this connection it 
should be noted that since the value of the specific acidity at the 
neutral point is 1, not zero, 1 is subtracted from §8.A. in all calcula- 
tions. It may also be remarked that the writer fully realizes that 
the uncertainty of measurements of Px and especially of L.R. does 
not justify placing much dependence on the values of C beyond the 
second decimal place. 
The specific acidity of these soils was found to range from 2.0. to 
39.8, the lime-requirement from 0.05 to 0.8, and C from 0.010 to 0.200. 
The lower values of C represent untreated soils, the higher, those 
treated with lime. This is interesting from the theoretical standpoint, 
for it means that the ratio between soluble and adsorbed hydrogen- 
ion, and accordingly the character of the soil colloids, varies widely, 
