View report page

72
slowing down through the diminution of the head of water in the large
tank. The tank had ultimately to be raised on to girders, and a small
supply tank fixed at a lower level. (2) The liquor to be electrolysed in
the large tank had to be stirred from time to time to keep the mixture of
an equal gravity throughout, more especially as for obvious reasons a
certain quanity of a solution of sodium hydroxide is added. To keep the
liquor stirred a large broad drilled plate of galvanized iron is used, one end
of which acts as the fulcrum when the other is lifted up by means of a
chain leading over pulleys to the ground, so that the attendant has only
now and again to pull the chain to lift the plate up and down instead of
running up and down the ladder and stirring the liquid with a rod.
(3) It is necessary to govern the electric current, which is taken direct from
the mains, on account of the density of the salt mixture to be acted upon
varying from time to time owing to temperature changes and consequent
changes in conductivity. This difficulty is got over by the current regulator.
(Fig. 3.) (4) To prevent shocks and waste of fluid whilst changing the
carboys, a special glass tap has been made. (Fig. 1.) (5) To prevent loss of
available chlorine the solution of sodium hydroxide drips into a specially
blown carboy at the same time as the fluid is running into it, and the two
fluids are mixed with a stirrer inserted through an aperture in the neck of
the carboy, and when the carboy is full a final mixing for about two
minutes is given by means of a stirrer fixed to gear wheels. (Fig. 1.) Before
the ebonite stirrers with rubber flaps were made, full carboys and half carboys
had to be shaken rapidly for 10 minutes, and this not always with the
best results as to bringing about the desired stability, for when sodium
hydroxide is added the precipitate falls to the bottom, and it is necessary
to render the solution milky throughout. (6) So far as oxychlorides are
concerned, the apparatus in 10 months had only been taken to pieces and
cleaned twice. Every day, after working, the electrolysers are emptied
by means of the mud holes by removing the rubber plugs, and the fluid
which is run out is kept to recharge the electrolysers. The electrolysers,
after being emptied, are washed out by means of a hose, and then until
the next working are kept filled with water, which softens any deposit
formed upon the electrodes, and before starting work the electrolysers are
emptied and washed out again, a matter which takes up a few minutes
every day before and after each working.
Balance Sheet and Stability of Fluid.
During twelve months (the apparatus was installed at the beginning
of February, 1906), some 17,000 gallons of fluid have been manufactured
of a strength between 4.0 and 4.5 grammes of available chlorine per
litre—1,000.