172 BOTANICAL GAZETTE [OCTOBER 
acidity. Through a comparison of these values, matching the 
specific acidity actually determined against that computed for those 
substances causing the acidity, a means of identifying, or at least 
indicating, the principal source of the acidity is described. 
3. The data indicate that only two compounds of oxalic acid, 
potassium binoxalate and calcium oxalate monohydrate, occur in 
the Rumex leaves examined. The percentages in which these salts 
occur are computed from the data for paints and total oxalate in 
the dried material. 
4. Attention is directed to the value of a crystallographic ex- 
amination in corroborating the results of the chemical work. It is 
believed that the scheme of investigation described should prove of 
value to analysts in examining drugs, foods, or feeding stuffs of an 
acid character. 
5. The presence of a natural indicator in the leaves of R. abys- 
sinicus, the aqueous solutions of which are pink in the natural acid 
solution, is noted. On adding a fixed alkali the solution changes its 
color through yellow to brown, becoming nearly black when dis- 
tinctly alkaline. 
The writer wishes to thank Mr. Paut G. Russet of the Office 
of Foreign Seed and Plant Introduction for making examination of 
this material possible, for furnishing information as to the history 
of the plant and its culture in this locality, and for providing the 
fresh foliage for analysis. Also acknowledgment is due Messrs. 
Deve and Kunke for their kindness in permitting the inclusion of 
notes of their work, and Dr. Wuerry for his helpful suggestions 
and for the crystallographic examination of the leaf material. 
BurREAU OF CHEMISTRY 
Wasaincton, D.C, 
LITERATURE CITED 
1. BARNETT, G. D., and Cuapman, H. S., Colorimetric determination of reac- 
tion of bacteriologic mediums and other fluids. Jour. Amer. Med. Assoc. 
70:1062. 1918. 
2. CLARK, W. M., and Luss, H. A., The colorimetric determination of 
hydrogen-ion concentration and its application in bacteriology. Jour. 
Bact. 221-34, 109-136, 191-236. 1917. 
