21 
platinum foil. On the other hand, such solutions, in the absence of 
platinum, suffered no reductions in the current of hydrogen alone. 
Then followed the beautiful discovery of Graham ( 197 - 198 ) in 1866 - 68 , 
that platinum and particularly palladium, and other metals to a 
slight extent, have the power of absorbing considerable amounts 
of hydrogen under the influence of moderate amounts of heat, or 
as the result of electrolysis. Furthermore, the hydrogen in these 
metallic combinations was recognized as active, in the sense that 
it could reduce iodine to hydriodic acid, ferric salts to ferrous salts, 
etc., changes which can not be effected by ordinary molecular hydrogen 
in the cold. According to Graham, the hydrogen under these con- 
ditions becomes polarized, its affinity for oxygen thereby being 
greatly increased. Such hydrogen, for example, was found to combine 
with ox}^gen even in the cold, with the production of water. Now 
in the course of his own investigations Hoppe-Seyler found that 
freshly prepared palladium hydride has the power of reducing copper 
sulfate to metallic copper, that it decolorizes a solution of indigo, 
and reduces potassium permanganate in neutral solution to manganese 
dioxide, or in acid solution to a manganous salt; that it converts 
quinone into quinhy drone and changes oxyhemoglobin to methemo- 
globin. He found further that these powerful reductions are brought 
about only when the palladium hydrogen compound is fresh; if 
allowed to stand it loses these properties, while it is still found to 
contain hydrogen. 
These reducing actions correspond entirety to those exhibited on 
dissolving zinc or tin in dilute acids; in other words, they are effected 
by nascent or active hydrogen. According to Hoppe-Seyler the 
most interesting reduction which can be effected by active hydrogen 
is that of molecular oxygen to water, whereby — OH or — O — O — H, 
and finallv water and active oxvgen, are formed successivelv. He 
found further that if one shakes some palladium foil saturated with 
hydrogen with a dilute starch paste containing potassium iodide 
and air, there is produced in a few moments a dark-blue solution of 
the iodide of starch. In other words, through the influence of the 
hydride of palladium, potassium iodide is oxidized by the oxygen 
of the air, a change which ordinarily takes place only with extreme 
slowness. If now the foil be boiled with water and heated to redness 
to expel the hydrogen, it no longer has the power to form the iodide 
of starch when shaken with a solution of potassium iodide and starch 
in contact with air. 
Similarly, indigo is oxidized to isatin and ammonia to ammonium 
nitrite, benzene to phenol and toluene to benzoic acid, when these 
several substances' in aqueous solution are shaken with air and 
palladium hydride. All of these changes go to show that we have 
here to deal with very vigorous oxidations, and it can not be doubted 
