When the voltaic arc plays between two metallic rheophores, of copper
for instance, each formed of a U-tube traversed by a rapid current of
cold water, and placed horizontally opposite each other, the following
facts are observed: The luminous power of the arc is considerably
weakened; it is reduced to a mere luminous point even when a current
of 50 to 75 Bunsen elements of the large pattern is employed. The arc
is very unstable and the least breath is sufficient to extinguish it.
If a leaf of paper is placed above the arc at the distance of 0.004 to
0.005 meter a black point is produced in a few moments, which spreads
and becomes a perforation, but the paper does not ignite. The arc
consists of a luminous globule, moving between the two rheophores up
and down and back again. The form of this globule, as well as its
extreme mobility, causes it to resemble a drop of water in a
spheroidal state. If we approach to the voltaic arc the south pole of
a magnet the arc is attracted to such a degree that it leaves the
rheophores and is extinguished. The same facts are observed in an
intense form on presenting the north pole of a magnet to the arc. The
quantity of ozone seems greater than when the arc is not refrigerated.
It is to be noted that notwithstanding the refrigeration of the
rheophores the flame of the arc is slightly green, proving that a
portion of the copper is burning. It becomes a question whether the
arc would be produced on taking as rheophores two tubes of platinum in
which is caused to circulate, e.g., alcohol cooled to -30°.--_D.
Tommasi._
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