consisting of two pans is
termed. The vapours discharged from the second vessel during boiling are
passed through pipes to the steam chamber of the third vessel (in a
"triple effect"), and there being condensed, create a partial vacuum in
the second vessel. The third vessel may also be heated by means of live
steam. The vapours arising from the last vessel of the evaporating
plant, or in the case of a "single effect" from the vessel, are conveyed
into a condenser and condensed by injection water, which is drawn off by
means of the pump employed for maintaining a vacuum of 28 inches in the
vessel.

In the most recent designs of large evaporative installations, the
vapours generated from the last vessel are drawn through a device
consisting of a number of tubes enclosed in a casing, and the latent
heat raises the temperature of the treated lyes proceeding through the
tubes to supply the evaporator.

It will thus be observed that the object of multiple effects is to
utilise all the available heat in performing the greatest possible
amount of work. Special devices are attached to the plant for
automatically removing the condensed water from the steam chambers
without the loss of useful heat, and as a precaution against splashing
over and subsequent loss of glycerine through conveyance to the steam
chamber, dash plates and "catch-alls" or "save-alls" of various designs
are fitted on each vessel.

In working the plant, the liquor in each vessel is kept at a fairly
constant level by judicious feeding from one to the other; the first
vessel is, of course, charged with treated lyes. As the liquor acquires
a density of 42 deg. Tw. (25 deg. B.) salt begins to deposit, and may be
withdrawn into one of the many patented appliances, in which it is freed
from glycerine, washed and dried ready for use at the soap pans.
Difficulty is sometimes experienced with the tubes becoming choked with
salt, thereby diminishing and retarding evaporation. It may be necessary
to dissolve the encrusted salt with lyes or water, but with careful
working the difficulty can be obviated by washing out with weak lyes
after each batch of crude glycerine has been run away, or by increasing
the circulation.

It is claimed that by the use of the revolving heater designed by
Lewkowitsch, the salting up of tubes is prevented.

The salt having been precipitated and removed, evaporation is continued
until a sample taken from the last vessel has a density of 6