RESEARCH METHODS IX STUDY OF FOREST ENVIRONMENT. 121 
Other Soil Properties to be Studied, 
acidity and alkalinity. 
While neither extreme acidity or alkalinity is often encountered 
in forest soils, because of their usually good drainage, *yet the subject 
is one that should not be overlooked, even though, on account 
of its relative unimportance, it must be given rather scant space. 
Unfortunately because of deficiencies in chemistry itself and a lack 
of proper understanding of the method by which the activity of acids 
in the soil might be measured, reliable results in such measurements 
bearing on problems of plant distribution are only just beginning to 
appear; for this reason, it is unsafe to say that the concentration 
of acids in the soil either is or is not an ecological problem distinct 
from the moisture-supply problems which have just been described. 
The suggestion of direct toxicity of soluble substances in the soil is 
frequently encountered, but so far as known no one has shown that 
toxic effects are not effects produced by the cessation of the water 
stream. It has also been frequently suggested that active acids or 
alkalis in the soil combine to withhold from the plant the substances 
needed for its nutrition. This seems more probable. Skepticism in 
these matters is designed primarily to indicate that such questions 
are still open to investigation from more than one angle. The 
methods for determining acidity and alkalinity in soils will be briefly 
reviewed, as though these were matters entirely independent of the 
subject of water supply. 
A recent and readily grasped article by Wherry (111) is filled 
with good suggestions on the vexed question of measuring the acidity 
of soils, and should be read by everyone who intends to go further 
with this discussion. Among his suggestions, an outline given by 
him to cover the various methods of acidity measurement will be 
followed, with some elaboration, also bringing up at appropriate 
points the corresponding methods applicable to the'determination of 
alkalinity. It should, perhaps, be explained that the term " alka- 
linity " is here used in its chemical sense, and not with the broader 
meaning, sometimes permitted, of total soluble salts. 
1. A salt solution is added to the soil. For this purpose there have been 
used sodium chloride, potassium chloride and nitrate, calcium chloride, nitrate 
and acetate, zinc sulphide plus calcium chloride, etc. The quantity of acid in 
the resulting solution, which represents that originally present in the soil plus 
a much greater amount produced indirectly by the processes 1S outlined is then 
determined by titration or other means. 
In the appendix to this paper has been given in detail the titra- 
tion method for acidity following the "extraction" of the acids of 
1S Briefly, replacement of H-ions in compounds which would in stable condition show 
no evidence of the weak acids present. 
