348 MODERN PAPER-MAKING
The rag washer uses a large amount of water, and this is not recovered, as
it contains traces of the soaps formed in the boiler and also a quantity of rag
fluff or fibres, but not sufficient to pollute a river. The rag breakers, where
most of the washing is done, also use a very large quantity of water, and this
is also not recovered, although if a wrapper machine is run at the mill some
of it can certainly be used with advantage for furnishing the beaters.
There is a very large amount of rag fibre lost here, due to the finer fibres
passing away through the meshes of the washing drums and the washer screens,
and also through the button and sand catchers, where these are fitted. The
loss sustained during this operation is serious and deserves more careful attention
than it generally receives.
It might possibly pay to recover this fibre in a save-all, and some of the
water used towards the end of the washing is quite clean enough to use again
if water is scarce. This would necessitate the use of large tanks and a pump
to return the water to the washer.
Immediately following the washing operation in the breaker comes the
bleaching, and this uses more water; where the bleached stock is run into
drainers or steeps the liquor from these latter should always be recovered,
when rags are being bleached, and run into tanks, whence it may be pumped
back to the potchers to start the next bleaching operation.
It is sometimes possible to use the spent liquor from three potchers to com-
plete the bleaching of the rags in a fourth potcher without the addition of any
fresh bleaching liquor, and this represents a great saving. This can only be
done, however, when more than the necessary amount of bleach is being used
in the first instance—i.e., when hurrying stock through the mill.
The beaters are usually furnished with new unused water, owing to the
fact that every care has to be taken to eliminate dirt, and to keep the shade of
the paper bright and constant. This does not, of course, apply to low-grade
papers, newsprint and printings, .and even in the case of fine papers sufficient
water should be available from the machine back-water system to furnish the
beaters.
At the machine all spray water from the strainers, water from the save-
alls beneath the wire and overflow water from the vacuum boxes should be
collected and run to an auxiliary strainer or "back knotter' and strained free
from lumps, knots of fibres, and rubber, and then pumped back to the stuff
box for diluting the thick stuff from the stuff cock. The careful conservation
of all this water represents an enormous saving in chemicals, such as engine
size, alum, dyes, loading and small fibres. It also reduces the effluent, which
must be disposed of ultimately. It also assists greatly in the reduction of froth
and the prevention of scale in the water service system when hard waters are