252	MODERN PAPER-MAKING
mixture of mechanical pulp and waste papers, the proportions being 25 per cent
face and 75 per cent backing.
In the drying of boards it is not the general practice to use dry felts, and on
some of the big modern machines, in order to save space, the drying cylinders
have been arranged in tiers, five or six high. We believe that this practice
originated in America, but we are not at all certain that it is an unqualified
success.
It is almost universal practice to combine a system of hot air with the dry
cylinders, in order to absorb the large amount of moisture given off into the
pockets between the tiers of the cylinders, and between the cylinders themselves.
On many board machines the paper is calendered on machine calenders, and
then cut at the end of the machine, instead of being reeled and cut separately.
This is not, as a rule, a difficult matter, as board machines run at a compara-
tively slow speed when compared with some modern paper-making machines,
although, of course, the output in weight may be very high.
In the case of triplex boards the usual furnish is face and backing of the
same material, such as sulphite, with a middle of poorer quality, such as straw-
boards and mixed waste papers.
This arrangement necessitates the use of only two sets of beaters and chests,
a great saving of space and power. The usual 'finish5 is a water-finish put
on with chilled iron rolls in two tiers on to which water is led from a trough.
Soap is usually added to the trough to prevent rusting. The paper passes
from the second stack moist, and the finish is put on during its passage through
the two remaining stacks. Four stacks of calenders have therefore to be
provided.
the 'mould' machine
The so-called mould machine is used for making imitation hand-made
papers, and papers made on these machines are the nearest approach to hand-
made paper which has yet been achieved by mechanical means.
The paper is, however, inferior to genuine hand-made paper.
It is possible on- this machine to make paper with a deckle edge all round
the sheet, and this fact alone is liable to mislead those who are not experts into
mistaking the *xnould' made for the real hand-made sheet
Great secrecy is observed in mills possessing these mould machines; the
wet cod, coasistemg of strainer> vat, wire-covered cylinder and presses, is placed
in a lodbed room, aad the wet web is led on a felt through a slit iii the wall
into the drying room.
lie *moakT or cylinder is just like a large-diameter dandy roll, and it
revolves partly submerged in the stuff in the vat.