1922] WALTON—AFRICAN SORREL 169 
Discussion 
Much may be learned about acid material of the same general 
type as the foliage of Rumex sp., merely from a determination 
of the total (or titrable) and the epeene acidity of a water 
extract of it. By “same general type” is meant here acid material 
in which, as in the sorrel, the “acidity” is due almost entirely to 
forms of a single acid. If, in addition to total and specific acidity, 
the total amount of the acid radical present in the water extract and 
in the material itself be known, it is possible to draw fairly accurate 
conclusions as to the quantities of the several salts of that acid 
actually present, without making elaborate determinations of 
the several basic elements. Auxiliary use of the petrographic 
microscope may afford valuable qualitative substantiation of the 
conclusions. 
In this investigation the mere determination of “degree of 
acidity’’ (total titrable acidity of the water extract) of the sorrel 
foliage meant little; the acidity might have been caused by the 
presence of free oxalic acid. Determination of the specific acidity 
(H-ion concentration), however, proved conclusively that the 
acidity of the water solution could not have been caused by the 
presence of the free acid; as for the normality involved, the spe- 
cific acidity value of oxalic acid would have been approximately 
ten times” the values actually found. On the other hand, the 
agreement between the “specific acidity’’ values determined experi- 
mentally for the sorrel extracts and those computed for pure solu- 
tions of potassium binoxalate of the same normality is striking. 
These values for potassium binoxalate solutions were computed by 
K Y) . 
? 
the help of the formula: Percentage ionization = 100( V KV- 
%° Computed from data reported by Tuomas (9) after Ostwatp (5). Oxalic acid 
of a dilution comparable with the water extract of sample No. 38339 (N Xo0.0172) is 
highly dissociated, the percentage ionized being 88.4 at 25° C., according to Tuomas’ 
table. 
* By an evident typographical error this formula in Tuomas’ article was incor- 
aoe 4 
rectly stated: “Per cent ionization=100V K oe ” The method of calculating 
the Px value is here appended in more detail, using as an example the data for the 
nat =. b &; , ‘2s 3: 4 re - 4 £4 7 g 7 Noi i. 
