New Measurer of Voltaic-Electricity 123

than water; for it is decomposed with facility when rendered
a better conductor by the addition of acids or salts; its elements
may in numerous cases be obtained and collected with-
out any embarrassment from secondary action, and, I
being gaseous; they are in the best physical condition f
for separation and measurement. Water,, therefore, >J
acidulated by sulphuric acid, is the substance I shall
generally refer to, although it may become expedient
in peculiar cases or forms of experiment to use other
bodies (578).

442. The first precaution needful in the construction
of the instrument was to avoid the recombination of
the evolved gases, an effect which the positive electrode
has been found so capable of producing (307). For this
purpose various forms of decomposing apparatus were
used. The first consisted of straight tubes, each con- *"'
taining a plate and wire of platina soldered together by lgt 2°*
gold, and fixed hermetically in the glass at the closed extremity

of the tube (fig. 20). The tubes were about eight
inches long, 0.7 of an inch in diameter, and gradu-
ated. The platina plates were about an inch long>
as wide as the tubes would permit, and adjusted as
near to the mouths of the tubes as was consistent
with the safe collection of the gases evolved. In
certain cases, where it was required to evolve the
elements upon as small a surface as possible, the
metallic extremity, instead of being a plate, con-
sisted of the wire bent into the form of a ring
(fig. 21). When these tubes were used as measurers,
they were filled with the dilute sulphuric acid,
inverted in a basin of the same liquid (fig. 22),
and placed in an inclined position, with their
lg" 2I" mouths near to each other, that as little decom-
posing matter should intervene as possible; and also, in such a
direction that the platina plates
should be in vertical planes

(455).

443. Another form of appar-
atus is that delineated (fig. 23).

The tube is bent in the middle; p. 22

one end is closed; in that end

is fixed a wire and plate, a, proceeding so far downwards, that,,

when in the position figured, it shall be as near to the angle as

re is no substance better fitted, under ordinary