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71
in order to justify the recommendation to the Council to expend public
money for such a venture.
The system adopted at Poplar is to mix a certain quantity of fluid in
an elevated tank and then to allow this fluid to flow through four double
troughs, or cells, placed one above the other, so that the liquid descends
continuously by gravity. Each trough is divided laterally by a partition,
and in each of the two divisions five distinct " elements " (consisting of
one positive and two negative plates) are suspended (Fig. 1). The positive
plates are of thin platinum wire wound upon slate slabs and the negative
plates are of zinc. There are thus four troughs, each containing ten
"elements," or 40 cells in all. The liquid enters through the funnel
visible towards the top left-hand side of the illustration, passes along the
front division of the top trough, back through the division behind, over a
weir and into a sub division, from which it is drawn off by the bent glass
tube discharging into the second funnel; it passes along the front division,
back through the division behind, over the weir into the pocket of the
second trough, and so on to the final bent tube, which discharges it into a
carboy. A bottle arranged at the right-hand side of the tier of cells
(shewn) supplies the sodium hydroxide used as a preservative, which flows
drop by drop into the carboy as it is filling and serves to neutralise free
hypochlorous acid. As the liquid passes through the troughs it is subjected
to the action of a regulated current of 15 to 17 amperes at 230 to
250 volts, being 5 7 to 6 2 volts per cell. During the run the liquid in the
carboy is thoroughly stirred by means of an ebonite rod provided with
rubber flaps (shewn).
The objects aimed at to make the working of the apparatus and the
manufacture of the fluid become simple and automatic were as follows:—
(1) To see at a glance whether the apparatus is working properly. This
is accomplished by a gauge glass in front of the large tank and another
gauge glass on the little supply tank (Fig. 1), the first to show the quantity of
salt liquor capable of being acted upon, and the second to show if the
liquor is running properly into and out of the small supply tank, as the
chloride of magnesium contains impurities which are likely to block up
the valve of the small cistern and the taps leading to and from the same.
A thermometer is kept in the small supply tank to see the temperature of
the salt liquor, and another thermometer is placed at the outgo of the last
electrolyser; the difference of the temperature gives the rise in temperature
due to the eloctrolysis, and which is found, when the apparatus is working
satisfactorily, to be under 30°F. The small tank is necessary to keep a
constant flow of the fluid into the electrolysers. When first the apparatus
was erected the fluid used to become unduly hot on account of the flow