Some studies made of the telegraph service of the Railway Company of
the East (France) have resulted in a happy modification of the Callaud
pile, rendering it easier of maintenance and reducing the consumption
of the materials employed.
As well known, the Callaud pile, which is exclusively employed for
telegraphic purposes by certain railroad companies, consists of a glass
vessel, of a circular piece of zinc suspended by hooks from the upper
part of the vessel, and of a strip of copper resting on the bottom of
the latter. This copper strip is riveted to a rod of the same metal
which constitutes the positive electrode. In the bottom of the vessel
there is placed a saturated solution of sulphate of copper, so that its
level reaches to within a short distance of the lower part of the zinc,
and the vessel is then filled with pure water. The zinc being attacked,
there is formed a zinc sulphate, which always remains at the upper part
of the vessel by reason of the difference in density of the solutions
of sulphate of zinc and sulphate of copper, and the reduced copper
deposits upon the strip in the center. It has been found necessary to
cover the copper rod with a sheath of gutta-percha in order to keep it
from being cut at the line of intersection of the two liquids, and this
is the first inconvenience of the system. It is necessary, moreover,
to keep the solution of copper at a certain degree of concentration by
placing in the bottom of the vessel a supply of crystals of sulphate
of copper. Hence it happens that the solution, being increased,
eventually reaches the zinc, and the latter is thereupon attacked to no
purpose, with a pure loss of copper through reduction. This is a second
inconvenience, which can be remedied by introducing into the pile
only a simply saturated solution without excess of crystals. It will
be seen that, in this latter case, it is necessary to visit the pile
quite frequently, to empty it by means of siphons, and to confide its
maintenance to experienced persons only.
This is why, up to the present, railroad companies have preferred
the Daniell to the Callaud pile for alarm bells that control signal
disks, despite the serious advantages of the Callaud pile and the
inconvenience of the porous vessel that enters into the composition of
the other.
[Illustration: NEW SULPHATE OF COPPER PILE.]
The modified Callaud pile is exempt from the defects that we have just
pointed out. It differs from the old form in the substitution of a
leaden tube, open at its extremities and dipping into the liquid of the
pile, for the piece of copper or positive electrode. The lead, which
is not attacked, and may serve indefinitely, is held in a vertical
position by means of a foot made by cutting slits with a pair of
scissors in the bottom of the tube, and bending back the strips thus
formed. This foot also serves to prevent the tube from touching the
zinc, by holding it in equilibrium.
In order to charge the element thus constituted, it is only necessary
to fill the lead tube with crystals of sulphate of copper and to pour
water into the glass vessel until its level reaches within a centimeter
and a half of the upper edge of the zinc. In an hour the copper will
have dissolved sufficiently to allow the pile to begin its action.
Experience has demonstrated that, whatever be the supply of copper that
is put into the lead tube, the saturated solution _will never reach the
zinc_, even in an open circuit.
In sum, the new arrangement given to the Callaud element presents the
following advantages: (1) It permits of the maintenance being confided
to anybody, since this consists simply in the introduction into the
central tube of crystals of sulphate of copper when it is seen that
the blue tint of the lower liquid is disappearing. (2) It permits of
proportioning the expense to the work really effected.--_La Nature_.
[Illustration: Lodges, Portington Grange, Eastrington.
Walter Hanstock, Architect.
GROUND PLAN.
CHAMBER PLAN.