RESEARCH METHODS IX STUDY OF FOREST ENVIRONMENT. 121 



Other Soil Properties to be Studied, 

 acidity axd alkalinity. 



While neither extreme acidity nor 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. 

 Unfortunatelv because of deficiencies in chemistrv 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 (141) 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 haA r e 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 solu- 

 tion, which represents that originally present in the soil plus a much greater amount 

 produced indirectly by the processes 18 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 



18 Briefly, replacement of H-ions in compounds which would in stable condition show no evidence of 

 the weak acids present. 



