JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. 9 JUNE 4, 1919 No. n 



PHYSICAL CHEMISTRY.— r/j^ statement of acidity and 

 alkalinity, with special reference to soils. Edgar T. Wherry, 

 Washington, D. C. 



In the course of observations on the acid and alkaline reac- 

 tions of soils supporting the growth of native plants, which the 

 writer has been making at odd times during the past several 

 years, considerable attention has been paid to the method of 

 presenting the results ; and it has been concluded that the usual 

 plans can be improved upon, especially from the point of view 

 of their ease of comprehension on the part of workers in non- 

 mathematical sciences. Certain suggestions in this connection 

 are put forward in the present note. 



Two dififerent methods of stating reactions are in general 

 use by chemists, the "concentration" and the "potential" meth- 

 ods. In the concentration method the number of gram equiva- 

 lents of hydrogen-ion per liter is stated, usually as an integral 

 power of 10 with a coefficient; in the potential method, the 

 exponent of 10, stated to one decimal place (which is directly 

 proportional to the electric potential produced by the hydrogen- 

 ion) is used alone. Thus, the acidity of a given solution might 

 be described as either 5.0 X io~® gram-equivalents of H"*" per 

 liter, or as Ph = 5.3. It^ takes, however, considerable effort 

 to appreciate the relative magnitude of quantities thus stated; 

 to tell off-hand, for instance, whether 5 X io~^ is greater or 

 less than 6 X io~^; to realize that a solution with Ph = 2.4 is 

 6300 times as acid as one with Ph = 5.6; and to recognize 

 whether a given solution is acid or alkaline in reaction without 

 considering the relation of the exponent to 7 (that of a neutral 

 solution) . 



305 



