; but being to us an elementary substance, it cannot be due
to its capability of suffering decomposition.

687. _Chloride of sulphur_ does not conduct, nor is it decomposed. It
consists of single proportionals of its elements, but is not on that
account an exception to the rule (679.), which does not affirm that _all_
compounds of single proportionals of elements are decomposable, but that
such as are decomposable are so constituted.

688. _Protochloride of phosphorus_ does not conduct nor become decomposed.

689. _Protochloride of carbon_ does not conduct nor suffer decomposition.
In association with this substance, I submitted the _hydro-chloride of
carbon_ from olefiant gas and chlorine to the action of the electric
current; but it also refused to conduct or yield up its elements.

600. With regard to the exceptions (679.), upon closer examination some of
them disappear. Chloride of antimony (a compound of one proportional of
antimony and one and a half of chlorine) of recent preparation was put into
a tube (fig. 68.) (789.), and submitted when fused to the action of the
current, the positive electrode being of plumbago. No electricity passed,
and no appearance of decomposition was visible at first; but when the
positive and negative electrodes were brought very near each other in the
chloride, then a feeble action occurred and a feeble current passed. The
effect altogether was so small (although quite amenable to the law before
given (394.)), and so unlike the decomposition and conduction occurring in
all the other cases, that I attribute it to the presence of a minute
quantity of water, (for which this and many other chlorides have strong
attractions, producing hydrated chlorides,) or perhaps of a true
protochloride consisting of single proportionals (695, 796.).

691. _Periodide of mercury_ being examined in the same manner, was found
most distinctly to insulate whilst solid, but conduct when fluid, according
to the law of _liquido-conduction_ (402.); but there was no appearance of
decomposition. No iodine appeared at the _anode_, nor mercury or other
substance at the _cathode_. The case is, therefore, no exception to the
rule, that only compounds of single proportionals are decomposable; but it
is an exception, and I think the only one, to the statement, that all
bodies subject to the law of liquido-conduction are decomposable. I
incline, however, to believe, that a portion of protiodide of mercury is
retained