te 
= 
4,0, DECOMPOSED 
308 BOTANICAL GAZETTE [OCTOBER 
(in the presence of hydrogen peroxide) of potassium iodide, pyro- 
gallol, and SpirzER’s reagent was likewise found to be equally 
catalyzed by platinum, whether it had been treated with active 
@ oxygen or with hydro- 
gen. 
The action of plati- 
num black in decom- 
posing hydrogen 
peroxide, however, was 
greatly modified by its 
previous treatment. 
The two electrodes, 
freshly platinized and 
subjected to active oxy- 
gen and hydrogen as 
before, were placed sepa- 
rately in flasks, each of 
1 which contained 100 cc. 
of o.1M hydrogen per- 
B oxide, to which a mix- 
ture of phosphates (5 cc. 
of o.1M NaH.PO, and 
: to cc. o. 1M Na, HPO,) 
90 me whe had been added in order 
to preserve the neutral- 
Fic. 2.—Curves showing decomposition of ; ve 
hydrogen peroxide: AB shows activity of plati- ity of the solution. 
num black which had previously been subjected the decomposition of the 
to active oxygen by using it as an anode; AC peroxide proceeded, por- 
shows action of platinum black which had previ- ‘ cating of & Ce 
ously been subjected to active hydrogen by using "ONS consis i g : 
it as a cathode; ordinates represent percentage each were pipetted out, 
of hydrogen peroxide decomposed; abscissae repre- acidified with H.SO, and 
ee titrated with potassium 
permanganate for the amount of hydrogen peroxide left in the 
solution."® The results are shown in fig. 2, where AB indicates 
%5 Since hydrogen peroxide reduces acidified potassium permanganate quantita- 
tively, the amount of the latter used in a titration is a measure of the unchanged per- 
oxide present in the solution. EvLER (Hofmeister’s Beitrige 7:1. 1908) has employed 
this method in the study of catalase. 
