[A] Annales de Chimie, tom. xxiv. p. 93.

[B] Ibid. tom. xxiii. p. 440; tom. xxiv. p. 380.

[C] Ibid. tom. xxiv. p. 383.

610. M. Doebereiner refers the effect entirely to an electric action. He
considers the platina and hydrogen as forming a voltaic element of the
ordinary kind, in which the hydrogen, being very highly positive,
represents the zinc of the usual arrangement, and like it, therefore,
attracts oxygen and combines with it[A].

[A] tom. xxiv. pp. 94, 95. Also Bibliotheque Universelle, tom. xxiv.
p. 54.

611. In the two excellent experimental papers by MM. Dulong and Thenard[A],
those philosophers show that elevation of temperature favours the action,
but does not alter its character; Sir Humphry Davy's incandescent platina
wire being the same phenomenon with Doebereiner's spongy platina. They show
that _all_ metals have this power in a greater or smaller degree, and that
it is even possessed by such bodies as charcoal, pumice, porcelain, glass,
rock crystal, &c., when their temperatures are raised; and that another of
Davy's effects, in which oxygen and hydrogen had combined slowly together
at a heat below ignition, was really dependent upon the property of the
heated glass, which it has in common with the bodies named above. They
state that liquids do not show this effect, at least that mercury, at or
below the boiling point, has not the power; that it is not due to porosity;
that the same body varies very much in its action, according to its state;
and that many other gaseous mixtures besides oxygen and hydrogen are
affected, and made to act chemically, when the temperature is raised. They
think it probable that spongy platina acquires its power from contact with
the acid evolved during its reduction, or from the heat itself to which it
is then submitted.

[A] Annales de Chimie, tom. xxiii. p. 440; tom. xxiv. p, 380.

612. MM. Dulong and Thenard express themselves with great caution on the
theory of this action; but, referring to the decomposing power of metals on
ammonia when heated to temperatures not sufficient alone to affect the
alkali, they remark that those metals which in this case are most
efficacious, are the least so in causing the combination of oxygen and
hydrogen; whilst platina, gold, &c., which have least power of decomposing
ammonia, have most power of combining the elements of water:--from which
they are led to believe, that amongst gases, some tend to _unite_ under t