Definite Electro-Chemical Decomposition 147

formed bichloride of tin (514), 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 connection
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

Fig. 29.

latter when washed was then reweighed, and the increase gave
the weight of the tin reduced.

526. 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 elec-
trode 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n carefully weighed, was sealed hermetically into a 1