202 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 11, NO. 9 



stants found by other methods of measurement. In the translation 

 of values from one experimental system to another the dissociation 

 constant of water is frequently involved. But this constant Wherry 

 introduces at the very beginning while the user of pH introduces it 

 only in a limited number of cases and when he wishes to make theoret- 

 ical calculations of the kind which the botanist (for whose benefit 

 xH was devised) has so far not employed. 



Our difference in point of view, then, if it can be traced beyond 

 matters which the future alone will balance properly, seems to rest 

 upon this. Wherry's xH scale presents to the student a symmetrical 

 picture easily grasped when approached with our habitual conception 

 of a vital distinction between acidity and alkalinity and when the 

 derivation is not attempted. The pH scale emphasizes the experi- 

 mental derivation of values and the actual continuity in the acid- 

 base system of equilibria. 



In the use of either scale there are involved difficulties in the experi- 

 mental setting up of the ultimate standards and recognizing this I 

 have taken care in my book to suggest (in Chapter XVII) that there 

 be, tentatively at least, agreement of the same nature that fixes our 

 scales of length and weight. But I fail to see how the difficulties 

 which are here involved are in any way lessened for the experimenter by 

 setting up a definition of a new reference point as Wherry has done in 

 choosing the hydrogen-ion concentation of pure water in place of nor- 

 mal hydrogen-ion concentration. 



Note by Wherry and Adams. 



We readily concede that the 1 : .']+ : 1(3 series has the real disad- 

 vantage of unfamiliarity, but so does the series 1 : 1.6 : 2.5 : 4.0 : 

 6.3 : 10 used by Clark. Trisection of the interval between 1 and 10 

 would give a series, 1 : 2+ : 5~ : 10, which is already familiar, 

 in coinage, and therefore preferable. 



But surely the use of specific acidities no more connotes lack of con- 

 fidence in the Xh scale than the measurement of electric current in 

 amperes implies disrespect to Volta, after whom the unit of electrical 

 potential is named. The Xh (potential) values may well be translated 

 into the corresponding specific acidities (quantities) whenever the 

 experience of the readers for whom a contribution is intended makes 

 the method of statement by quantities more readily understandable. 



Edgar T Wherry and Ei^LioT O. Adams 



