.MANGANESE CHLOEOSIS OF PINEAPPLE. 
25 
the hydrogen-ion concentration of the solution is determined at 
various stages of titration with sodium hydroxid. Ferrous hydroxid 
was not precipitated until the solution was made quite alkaline. 
Ferric salts could not be investigated with the hydrogen electrode, but 
Hildebrand predicts "that they would behave very much like 
aluminum salts/' which are precipitated while the solution is still 
/.O 
2.0 
&o 
4.0 
^ 7.0 
8.0 
9.0 
/ao 
MO 
TO /=>£J?NT<S. 
F£T*/?06& //?M JV/9S 0£- 
il 
X 
rt/GHL Y C/JLCfffi£- 
OC/S SO/LS. 
/O 
ao <3o *o 
KfO 
eo 
Fig. 5.— Titration curves of ferric and ferrous salts with alkali. 
strongly acid. This work of Hildebrand seems to furnish a clue to 
the manner in which chlorosis is induced. 
In order to investigate this more fully the titration curve of ferric 
chlorid was determined. Various amounts of 0.2N sodium hydroxid 
were added to 50 cubic centimeter portions of a roughly 0.2 X solu- 
tion of ferric chlorid. The solutions were filtered and the hydrogen- 
ion concentration of the filtrate was determined by the colorimetric 
method of Clark and Lubs (11). This titration curve for ferric 
chlorid is given in Figure 5. By careful titration, it was easy to 
