that it could
not by any shake of the hand or apparatus touch the negative electrode at
the bottom of the vessel. The whole arrangement is delineated in fig. 69.

790. Under these circumstances the chloride of tin was decomposed: the
chlorine evolved at the positive electrode formed bichloride of tin (779.),
which passed away in fumes, and the tin evolved at the negative electrode
combined with the platina, forming an alloy, fusible at the temperature to
which the tube was subjected, and therefore never occasioning metallic
communication through the decomposing chloride. When the experiment had
been continued so long as to yield a reasonable quantity of gas in the
volta-electrometer, the battery connexion was broken, the positive
electrode removed, and the tube and remaining chloride allowed to cool.
When cold, the tube was broken open, the rest of the chloride and the glass
being easily separable from the platina wire and its button of alloy. The
latter when washed was then reweighed, and the increase gave the weight of
the tin reduced.

791. I will give the particular results of one experiment, in illustration
of the mode adopted in this and others, the results of which I shall have
occasion to quote. The negative electrode weighed at first 20 grains; after
the experiment, it, with its button of alloy, weighed 23.2 grains. The tin
evolved by the electric current at the _cathode_: weighed therefore 3.2
grains. The quantity of oxygen and hydrogen collected in the
volta-electrometer = 3.85 cubic inches. As 100 cubic inches of oxygen and
hydrogen, in the proportions to form water, may be considered as weighing
12.92 grains, the 3.85 cubic inches would weigh 0.49742 of a grain; that
being, therefore, the weight of water decomposed by the same electric
current as was able to decompose such weight of protochloride of tin as
could yield 3.2 grains of metal. Now 0.49742 : 3.2 :: 9 the equivalent of
water is to 57.9, which should therefore be the equivalent of tin, if the
experiment had been made without error, and if the electro-chemical
decomposition _is in this case also definite_. In some chemical works 58 is
given as the chemical equivalent of tin, in others 57.9. Both are so near
to the result of the experiment, and the experiment itself is so subject to
slight causes of variation (as from the absorption of gas in the
volta-electrometer (716.), &c.), that the numbers leave little doubt of the
applicability of the _law of