1916] REED—OXIDASE ACTION 57 
mechanism of this reaction, however, has been quite unknown. 
A suggestion in regard to it was made by BAcu and CHopart,? who 
found that an excess of either peroxidase or hydrogen peroxide had 
no effect on the rate at which pyrogallol was oxidized by hydrogen 
peroxides and horse-radish peroxidase. They concluded that the 
peroxide and peroxidase always take part in the reaction in constant 
proportions. BacH and CuHopart thus arrived at the conclusion 
which had previously been advanced by KASTLE and LOEVENHART 
(l.c.) from theoretical considerations, namely, that the peroxidase 
forms a definite compound with hydrogen peroxide, exhibiting 
more energetic oxidizing properties than the peroxide alone. 
The writer has obtained results of a much more definite and 
conclusive character by experimenting with platinum black and 
by applying the suggestions gained in this way to the study of 
enzyme reactions found in living tissue. The present paper con- 
tains an account of the experiments with platinum black. 
In connection with certain experiments it was observed that 
different samples of colloidal platinum and colloidal silver (pre- 
pared by passing a direct current between two electrodes of the 
metal under water) behaved differently toward solutions of gum 
guaiac. In some cases the guaiac was oxidized directly, in others 
only after the addition of a peroxide. This condition suggested 
to the writer that samples of colloidal metal might contain different 
proportions of oxygen, and, moreover, that the amount might be 
varied by suitable treatment. Subsequent experimentation has 
proved this supposition to be correct. 
Instead of a solution of colloidal platinum, a platinum surface 
covered with the colloidal metal has been employed. A large 
platinum crucible with a surface of about 150 sq. cm. was platinized 
in the ordinary manner, by making it a cathode in a solution con- 
taining 2 gm. platinum chloride and 0.16 gm. lead acetate in 60 cc. 
of water, until its surface was uniformly coated with a black deposit 
of the colloidal metal. It was then subjected to active hydrogen 
by making it a cathode in a dilute solution of hydrochloric acid 
through which was passed a current of one ampere at 110 volt. 
To prevent the oxygen generated at the opposite pole from reaching 
* Ber. Deutsch. Chem. Gesells. 37:1342-1348. 1904. 
