1922| WALTON—AFRICAN SORREL 27% 
PFEFFER (6) of decrease in acidity in plant tissues (in life) and in 
sap, due to a rise in temperature (from 15° to 45°) and to exposure 
to sunlight, fully explains a loss in acidity of this magnitude, on 
drying fresh material in which the cells are still functioning. 
From the figures obtained for total oxalate it becomes apparent 
that there is more oxalate present in the leaves than is accounted 
for by the potassium binoxalate. Further, this excess oxalate 
must be either insoluble or neutral in reaction if soluble. Again 
the crystallographic-optical examination made by WHERRY decides 
the point. The only normal oxalate found was the insoluble calcium 
salt. A recapitulation of analytical results is presented in table VI. 
TABLE VI 
ANALYSIS OF LEAVES OF Rumex abyssinicus 
bs, ta; 
Percentage cromte calcium . Degree of acidity 
Leaves : = at bacaicinkis oc to o (ec. hoe gia 
_ ot aies ate 
EY hg (HKC.0,) (Ca C.0,. H.0 HO) 
Smaller << (fresh). ou 90.77 1.82 0.73 £529 
Larger leaves (fresh). . 89.50 2.05 0.53 185.4 
Smaller waa (after drying). 2.99 19.09 7.80 1490.0 
Larger leaves (after drying). 2.50 19.22 4.98 1500.0 
A discussion of the influence of such quantities of oxalate on the 
edibility of the sorrel foliage, or of the physiological effects following 
its use as food, is outside the scope of this paper. 
Summary 
1. The study here reported of the acidity and oxalate content of 
the leaves of Rumex abyssinicus (an African sorrel) demonstrates 
the advantages of determining the specific acidity (H* concentra- 
tion), as well as the total (titrable) acidity of a water extract of acid 
material of this nature. 
2. This paper brings together descriptions of relatively simple 
procedures, worked out by the investigators cited, for (1) colori- 
metrically determining, without the use of buffer solutions, the 
specific acidity of such water extracts, and (2) computing, for pur- 
poses of comparison, the specific acidity and P; value of pure solu- 
tions of the acid substance suspected of being the source of the 
