186	MODERN PAPER-MAKING
vacuum required on a suction box is never very high, and where there are long
runs on the same furnish with the same amount of water.
When a wire is being changed, all the boxes should be cleaned, examined
and tested for loose or worn bars or protruding ends, and if necessary these
should be carefully planed level, or changed by a man experienced at this
work. All bars with hard, soft or damaged places, or with knots, should be
discarded, as they will make ridges in the wire and cause loss of suction.
To obtain efficient and steady suction, the boxes must be carefully levelled
to each other and to the last tube roll. The guide roll should be slightly lower
than the last box, little more than the thickness of the wire; the latter will not
then be dragged hard over the edge of the last box and the guide roll will have

[James Bertram and Sons Ltd.
•fig 68.—the *aquair* vacuum pump for suction boxes and couch Roixs
This pump is specially designed to deal with air and water
a good grip of the wire and have more control over it. Sufficient space is left
after the first box to ran the dandy roll; aU succeeding boxes should then be
as close together as possible.
The first box is the most important. It is often said: "The first box makes
the paper/ While this is far from being correct, there is no doubt that the
appearance of the sheet is mostly controlled by the regulation of the suction
on this box. Too much suction gives a cloudy-looking paper, too little a
crushed or greasy appearance; in the first case, tie water mark will be faint
or absent altogether; in the second, it wiU be very muddled.
Apart from the first box, which has this special function, the other Boxes
should have the section divided between them as far as possible, though in
practice it will be found generally that one will stand more than the other.
If one box is being overworked, it will commence to vibrate with a hum-