NEWSPRINT 277

be kept in mind that practically all the moisture has to be removed by using
air as a carrier. Water dissolves in air, and the higher the temperature of the
air, the greater the quantity of water it can carry without becoming saturated.
This mechanism of drying is entirely different from drying by ebullition, and
it is doubtful whether any substantial proportion of the water removed from
the sheet in a news machine is boiled off. Adequate supplies of hot air efficiently
circulated and removed after becoming saturated, or nearly saturated, are
therefore essential for satisfactory drying.

FIG. 121.—VIEW OF THE DRY END or A FOURDRINIER MACHINE EQUIPPED WITH A
MINTON VACUUM DRYER
News machines built to run at the high speeds prevalent to-day are usually
equipped with about fifty, or in exceptional cases as many as sixty, 5-foot
dryers. It is generally considered that felt dryers are not an advantage, although
there is some difference of opinion on this matter. The last cylinder is usually
arranged as a sweat cylinder for damping the underside of the sheet. This is
especially important when making M.F. paper. Dry felts are used throughout
the dryer section, with the exception that on some machines it has been found
beneficial to omit the first bottom section felt, the idea being that free move-
ment of air past the sheet, at this stage, is more important than pressing the
paper hard against the cylinders by means of a felt.
The difficulties of arranging for uniform ventilation, and therefore uniform
drying, in conventional dryer parts, were overcome a few years ago by the
introduction of the Minton vacuum dryer. Although very few paper machines