The juice is brought to the boiling point,
and as much of the scum is removed as can be taken quickly. The scum is
returned to the diffusion cells, and the juice is sent by a pump to the
top of the building, where it is boiled and thoroughly skimmed. These
skimmings are also returned to the diffusion cells.
This method of disposing of the skimmings was suggested by Mr.
Parkinson. It is better than the old plan of throwing them away to
decompose and create a stench about the factory. Probably a better
method would be to pass these skimmings through some sort of filter, or,
perhaps better still, to filter the juice and avoid all skimming. After
this last skimming the juice is ready to be boiled down to a thin sirup
in
THE DOUBLE EFFECT EVAPORATORS.
These consist of two large closed pans provided within with steam pipes
of copper, whereby the liquid is heated. They are also connected with
each other and with pumps in such a way as to reduce the pressure in the
first to about three fifths and in the second to about one fifth the
normal atmospheric pressure.
The juice boils rapidly in the first at somewhat below the temperature
of boiling water, and in the second at a still lower temperature. The
exhaust steam from the engines is used for heating the first pan, and
the vapor from the boiling juice in the first pan is hot enough to do
all the boiling in the second, and is taken into the copper pipes of the
second for this purpose.
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