226	MODERN PAPER-MAKING
extra water which is used and the extra time the stuff is under the influence
of the shake give the shake more opportunity of bringing the fibres into an end-
on position. Ledger and other strong papers made on a 50-feet wire have a
more pronounced difference in breaking strain across and along the sheet than
those made on a 4O-feet wire, and it also is more difficult to give the sheet
the characteristic look of strength combined with clear water-mark which is a
feature of good ledger papers. If it is desired to give to a paper made from
rather poor stock the appearance of strength, a deep dam behind the slices will
cause the stuff to rush well up the wire and get very little result from the shake.
It will then look strong because the dandy roll has no nice level surface to
impress, and the fibres will be arranged in all directions, but it will have less
strength than if made a closer-looking paper.
In trying to make a close, well water-marked sheet from stuff that is not
well fibrillated, extra water and shake will be effective only up to a certain
point. That point has been reached when' the fibres are not settled into a com-
pact body before reaching the suction box. Less shake may be tried, or if
shake is known to be not above normal, less water is wanted.
Too much water and too little shake, or either alone, are shown by the
formation of water drills. These are thin streaks made by the water running
in channels along the wire and refusing to amalgamate with the stuff. More
often too much water is the cause. But a wire that is dirty in streaks, or badly
beaten stuff, will also give the same trouble.
Stuff that is beaten very fine—i.e., very much cut by the beaters—is easily
water-marked, and looks 'wet' on the wire, but is shown to be free when
passing over the suction boxes. This style of beating and paper-making makes
a very nice close sheet and a clear, bright water-mark, but the strength is very
poor for the quality of the stock used. Water drills are very often prominent
•<• in stuff of this description.
It may be mentioned in passing that fresh water is more productive of water
drills than the softened back water of the machine; also, if fresh water has to
be used to supplement the back water of the machine, it is much more difficult
to make a close sheet.
In making an engine-sized paper the slices have to be closer to the wire
tbn would be otherwise desirable, in order to keep back the froth which
forms on Ate breast of the machine. Very often with strong stuff, and with
papess containing a large proportion of wood fibres that have been kept a good
fe&gdi m die beater, numberless clear specks and spots appear in the paper.
These arc caused by die chemical action of resin, alumina, hard water, etc*,
'forming carbonic ackl gas (CO.). This formation of gas takes pkce on the
wire itself as well as before it The little bubble of gas keeps the fibres from