966 REPORT—1885. 
from molecule to molecule, until free hydrogen appears at the point of contact of 
oxygen, platinum, and liquid in the other tube, and unites with oxygen to form 
again a fresh molecule of water. 
Now if indigo-sulphonic acid be present in the acid, it is noticeable after a day 
or so that the indigo is decolorised when in contact with oxygen, being in all 
probability converted into isatine, but when in contact with hydrogen no action 
takes place. The hydrogen therefore does not reduce indigo when it is in the act 
of combining with oxygen, 
If, on the other hand, the conducting liquid be a saturated solution of common 
salt, and the reacting gases chlorine and hydrogen, the indigo becomes decolorised 
in both tubes, the bleaching taking place from above downwards. Of course 
decolorisation takes place at once on admission of chlorine, but it is not until some 
time has elapsed that reduction by the hydrogen becomes evident. Hydrogen 
appears therefore to possess the power of reducing indigo when it isin the act of 
combining with chlorine. 
Further experiments were made in order to ascertain whether other substances 
would comport themselves like indigo. Acid coloured with potassium permanganate 
was employed, and it was found that in both tubes decolorisation was to be 
noticed. he decolorisation of permanganate can take place only by reduction, 
and it must therefore be concluded that on the one hand hydrogen deprived it of 
its oxygen, and that on the other the action was due either to nascent oxygen, to 
ozone, or to hydrogen peroxide. 
A blank experiment was then made; hydrogen, potassium permanganate, and 
platinum were left in contact, and it was found that in a few hours the permanganate 
became colourless. To decolorise permanganate, therefore, does not require the 
ordinary arrangement of a gas-battery ; the feeble currents in the platinised platinum, 
or possibly the action of occluded hydrogen, are themselves sufficient to cause 
reduction and the union of the hydrogen. 
A similar experiment was made with oxygen, platinum, and permanganate; 
after thirty-six hours the permanganate had not lost its colour. The couple 
appears therefore to be necessary to the formation of active oxygen, whether it be 
in the state of ozone or of hydrogen dioxide. 
Experiments were also carried out with a solution of iodine in acidified potas- 
sium iodide, with similar results; hydrogen in contact with platinum alone reduced 
the iodine to hydriodic acid, but oxygen alone had no action. The solution on the 
oxygen side of the couple was however decolorised, although oxygen in contact 
with platinum had no action. With ferric chloride also the reaction was in all 
respects analogous. The results with indigo are therefore the only ones from 
which a conclusion can be drawn as to the action of the couple. The hydrogen is 
inactive when the couple consists of hydrogen and oxygen, but active when the 
couple consists of hydrogen and chlorine. Now to what cause is this difference in 
behaviour to be ascribed ? The gaseous hydrogen is in both cases the same; the 
production of sodium hypochlorite on the hydrogen side is improbable, inasmuch 
as the formation of ozone or hydrogen dioxide on the hydrogen side is excluded 
when the hydrogen-oxygen couple was employed. 
I would suggest as a possible explanation of this action that when a molecule 
of hydrogen reacts with a molecule of chlorine to form hydrogen chloride, atomic 
hydrogen must exist for a short interval of time. This atomic hydrogen, in the 
normal state, would at once combine to form molecular hydrogen, but in presence 
of indigo, indigo-white is produced by the union of the atomic hydrogen with 
indigo, as is usual when indigo is placed in contact with nascent hydrogen. But 
on the other hand, when a molecule of oxygen reacts with two molecules of hydrogen 
to form two molecules of water, it may be possible for the molecule of hydrogen 
to unite with the oxygen without assuming the atomic or nascent condition, and 
hence there is no reducing action on the indigo, But the oxygen must assume the 
nascent or active condition, and it is impossible to say whether its bleaching action 
on indigo is to be ascribed to direct action or to the formation of such intermediate 
products as ozone or hydrogen dioxide. 
It may perhaps be objected that it is unnecessary to bring in the idea of a 
