BLEACHING 47

in diameter, giving access to the circulating pump, which is a very efficient
apparatus, and can deal with the whole of the contents of the tower in a quarter
of an hour. There is a valve provided to shut off the contents of the tower
should the pump have to be dismantled, and also a wash-out valve for cleaning
. purposes.

The illustration (Fig. 10) clearly shows the lay-out of the complete system.
The pulp or grass is broken up and washed in the breaker, and is then con-
centrated by removing water with the drum washers, emptied and pumped
into the first tower, to which the strong bleach is added, or the first tower

[Messrs. Masson, Scott and Co. Ltd.
FIG. io.—BATTERY OF MASSON-SCOTT BLEACHING TOWERS WITH POTCHER AND CONCENTRATOR
may simply be used as a collecting tank for raw pulp, which is passed on and
bleached in the second tower. When the bleach is added, the pulp may be
circulated on to the next tower, and so on, until it reaches the last tower, or
if necessary it may be circulated round several times in the first tower by the
arrangement of pipes and a two-way cock. When the pulp is discharged
from the pipe into the top of the tower, it strikes a conical spreader pkte,
which mixes it thoroughly and helps to exhaust the bleach. By the time the
pulp reaches the last tower it should be thoroughly bleached, and a sample
may be taken to examine the colour. If it is not sufficiently bleached, a further
lot of bleach liquor may be added, and the contents circulated round the last
tower several times until the bleaching is completed.