260 MODERN PAPER-MAKING
and water drained away from the presses. For safety a supply should be avail-
able considerably in excess of this rather economical quantity of 2000 gallons
per ton. It should, however, be the aim to keep the water consumption on the
machines to as low a figure as possible, not so much because water may be
difficult to obtain, as because extravagance will almost invariably be linked
with excessive fibre losses. Modem newsprint manufacture, calls essentially
for a closed back-water system, which means that as large a quantity as possible
of the water should be used over and over again. Any water added in excess
of that subsequently removed by the machine (principally at the dryers) will be
wasted water, and unless an efficient fibre recovery system is available, the loss
involved is likely to be serious. "With an adequately balanced water system,
a recovery unit is not, as a matter of fact, essential.
The quality of the water used for the actual paper-making process, as distinct
from the boiler plant, is not of material importance. It should, of course,
be clear, and free from suspended matter, but it may be very hard without
giving any serious paper-making troubles. Indeed it is contended in some
mills that hard water has certain definite advantages over soft water, such as
helping to prevent pitch troubles on the machines. A typical hard water, quite
satisfactory for newsprint manufacture, is as follows:
Ca ....................9.7 parts per 100,000
Mg ....................3.2 „ „
Ci ....................9-<5 ,.....
S04 ....................2.1 „ „ „
Hardness, permanent................ 10.0 „ „
temporary................ 27.2 „ „
Preparation of Alum, Loading, and Dyes for Addition to Stock.—The most efficient
practice in newsprint mills to-day demands that all the auxiliary materials,
loading, alum, and in many cases dyestuffs, should be added to the stock in.
suspension or in solution.
China clay, as already mentioned, is mixed into a slurry with water, in the
clay-mixing house, which should be adjoining the clay store. The clay is
mixed in tanks, fitted with the necessary agitator gear, to give a concentration
of about 2 Ib. per gallon. From the mixing tank the slurry is pumped
through a screen, usually made of old machine wire, to a storage taak. The
slurry must, of course, be continually agitated to prevent sedimentation. In
some installations it is found convenient to have two or three mixing tanks,
ead* feeding one large storage tank. From the storage taak, the slurry is
pumped to a small service tank in the mill, which supplies the machines by
gravity. To preveat sedimentation, slurry from the service tank overflows
continuously, die surplus being collected in a receiving tank, from which it is
ptimf>ed back to dbe storage tank in the clay-house. The slurry is added to