188 ' MODERN PAPER-MAKING

Though no water can be seen to be squeezed out until the nip is reached,
there is no doubt that the pulp conies under the pressure sufficient to give it
a certain stability and allow more weight to be put on the top couch roll.
Most modern machines carry the top roll on swinging brackets, and levers
for additional weights are attached to these. This is quite a mistake. More
efficient couching can be obtained by putting the connections for the levers
on the spindle itself so as to bring the line of pressure through the centres of
both rolls as nearly as possible. Many machines do not use a cover on the
bottom roll. This may not matter for cheap papers, where wire-marking is
not considered of much consequence, but it is false economy where fine papers
are concerned. A cover prevents crushing, gives more bulk and a closer under
side, and does not obliterate the water-mark to the same extent as a bare roll
does. This is accounted for by the increased pressure surface owing to the
'give' of the woollen cover.

When putting on a new cover, the roll should be thoroughly cleaned with
hot water and the perforated holes in the shell cleaned out If the water has
been hot enough the roll will soon dry, or it may be wiped dry with a clean
rag. The end over which the cover has to be drawn requires special atten-
tion, lest any bit of stuff or grease or chip of wood from the wooden end be
pulled in and thus make a lump inside it. The cover should be temporarily
fixed at the front side. It must then be pulled tight to the back side and per-
manently fixed there. The front side is then loosened and also pulled tight
and permanently fixed. Whether it is tacked on to the wooden ends or roped
on, it should be free to travel round the roll. Boiling water is necessary for
the proper shrinkage of a new jacket, and quantity should not be stinted. If
the cover has a nap—though this is not a necessity for a bottom roll—it should
be in the running direction of the wire, so that the drag of the latter smooths
out the fibres instead of ruffling them up. Sometimes a cover is tight and
difficult to pull over the roll. Powdered starch or dry china cky well rubbed
over the roll will help to make it slip on more easily. But if this happens
often the manufacturer should be notified and will be able to correct the size.
Alter the cover has been shrunk, it is very necessary to go all over it carefully
with dbe fingers lest there should be any hard knot in the wool or any substance
wdemeath. Hard knots and wood splinters are not uncommon in covers
and should be pkfeed out with a sharp-pointed knife. Neglect of this precau-
tion means a ridged wire in the space pf an hour's work. This applies to both

It urifi gready assist die starting of a new top jacket if tHe nap is gently
brashtd tf^ rtamiag way, mone especially on die two places where the jacket
has beoa ftdded, and wfckli hpne a tetKlency to stand up. If the covers are