to a much higher temperature. The pan is generally filled with
distilled coal tar, and the heating is regulated in such a manner that
the temperature of the impregnating mass is raised far beyond 212°
Fahrenheit. This accelerates the penetration, which takes place more
quickly as the degree of heat is raised, which may be almost up to the
boiling point of the tar, as at this degree the paper is not destroyed
by the heat. In order to prevent the evaporation of the volatile
ingredients of the tar, the pan is covered with a sheet iron cover,
with a slot at the place where the paper enters into the impregnating
mass and another at the place where it issues. The tar is always kept
at the same level, by occasional additions.

The roll of paper is mounted upon a shaft at the back end of the pan,
and by suitable arrangement of guide rollers it unwinds slowly, passes
into the tar in which it is kept submerged. The guide rollers can be
raised so that when a new roller is set up they can be raised out of
the tar. The end of the paper is then slipped underneath them above
the surface of the tar, when having passed through the squeezing
rollers, it is fastened to the beaming roller, and the guide rollers
are submerged again. A workman slowly turns the crank of the beaming
roller.

This motion draws the paper slowly through the fluid, the roll at the
back end unwinding. The speed with which the squeezing rollers are
turned is regulated in such a manner that the paper remains
sufficiently long underneath the fluid to be thoroughly impregnated
with it. The workmen quickly learn by experience how fast to turn the
crank. The hotter the tar, the more rapid the saturation; the high
degree of heat expels the air and evaporates the hygroscopic fluid in
the pores of the paper. The strong heating of the tar causes another