The mass sets in a short time, or very rapidly by the action of heat,
and gives porous blocks of a solidity increasing with the quantity of
cement employed (5 to 10 per cent.).

[Illustration: FIG. 2.]

Fig. 2 represents an arrangement with blocks. The jar V, is provided
with a cover of copper, E, screwing into the glass. This cover carries
two vertical plates of sheet-iron, A, A', against which are fixed the
prismatic blocks, B, B, by means of India rubber bands. The terminal,
C, carried by the cover constitutes the positive pole. The zinc is
formed of a single pencil, D, passing into a tube fixed to the center
of the cover. The India rubber, G, is folded back upon this tube so as
to make an air-tight joint.

The cover carries, besides, another tube, H, covered by a split
India-rubber tube, which forms a safety valve.

The closing is made hermetical by means of an India rubber tube, K,
which presses against the glass and the cover. The potash to charge
the element is in pieces, and is contained either in the glass jar
itself or in a separate box of sheet-iron.

Applying the same arrangement, we form hermetically sealed elements
with a single plate of a very small size.

The employment of cells of iron, cast-iron, or copper, which are not
attacked by the exciting liquid, allows us to easily construct
elements exposing a large surface (Fig. 3).