sing solution of ammonia instead
of solution of potassa; and as it, when pure, is like water, a bad
conductor (554.), it was occasionally improved in that power by adding
sulphate of ammonia to it. But in all the cases the results were the same
as before; decompositions of the same kind were effected, and the electric
current producing these was in the same direction as in the experiments
just described.

935. In order to put the equal and similar action of acid and alkali to
stronger proof, arrangements were made as in fig. 80.; the glass vessel A
contained dilute sulphuric acid, the corresponding glass vessel B solution
of potassa, PP was a plate of platina dipping into both solutions, and ZZ
two plates of amalgamated zinc connected with a delicate galvanometer. When
these were plunged at the same time into the two vessels, there was
generally a first feeble effect, and that in favour of the alkali, i.e. the
electric current tended to pass through the vessels in the direction of the
arrow, being the reverse direction of that which the acid in A would have
produced alone: but the effect instantly ceased, and the action of the
plates in the vessels was so equal, that, being contrary because of the
contrary position of the plates, no permanent current resulted.

936. Occasionally a zinc plate was substituted for the plate PP, and
platina plates for the plates ZZ; but this caused no difference in the
results: nor did a further change of the middle plate to copper produce any
alteration.

937. As the opposition of electro-motive pairs of plates produces results
other than those due to the mere difference of their independent actions
(1011. 1045.), I devised another form of apparatus, in which the action of
acid and alkali might be more directly compared. A cylindrical glass cup,
about two inches deep within, an inch in internal diameter, and at least a
quarter of an inch in thickness, was cut down the middle into halves, fig.
81. A broad brass ring, larger in diameter than the cup, was supplied with
a screw at one side; so that when the two halves of the cup were within the
ring, and the screw was made to press tightly against the glass, the cup
held any fluid put into it. Bibulous paper of different degrees of
permeability was then cut into pieces of such a size as to be easily
introduced between the loosened halves of the cup, and served when the
latter were tightened again to form a porous division down the middle of