THE MANUFACTURE OF SOOT BLACK WITHOUT CHAMBERS.
A certain temperature is necessary for the combustion of every
substance; if a cold body is placed in the flame of a candle or an
oil lamp it becomes covered with soot, because it cools the flame to
such an extent that the carbon is no longer heated to the temperature
necessary for its combustion, and is, therefore, separated in a finely
divided condition. Use is made of this phenomenon in a method of making
soot black which has many advantages, of which the most important is
that expensive buildings are not required, and the manufacture can be
conducted in restricted space.
[Illustration: FIG. 33.]
A convenient arrangement for obtaining black by this process is
represented in Fig. 33. The thin-walled hollow cast-iron cylinder is
turned smooth on the outer surface, and is surrounded by a sheet-iron
cover at the distance of a few centimetres; it rotates in bearings,
which, like the spindles, are hollow; cold water is thus led through
the cylinder from a tank at a higher level. Below the cylinder are
placed, near to one another, smoking lamps, and at the side of the
cylinder is a broad brush of soft hair which continuously removes the
soot deposited on the surface, which then falls over an inclined plate
into the collecting vessel. The cylinder is kept in slow rotation by
any mechanical arrangement. The lamps are devised not to produce a
hot flame, but when this comes in contact with the cold surface of
the cylinder, it deposits a ring of soot on the rotating cylinder
which is then removed by the brush. The cylinder is kept cooled by
the water which runs through it. The soot which is collected shows a
tolerably strong brown shade in consequence of the rapid cooling of the
flame, which causes the formation of a large quantity of products of
distillation; the soot will always require ignition.
[Illustration: FIG. 34.]
It has been proposed further to simplify the manufacture of soot black
by this method, by burning coal gas under the cylinder from numerous
small openings in a pipe. Coal gas indeed gives a very fine deep black,
but the yield is so small that this process could never be adopted with
advantage.
The apparatus constructed by Thalwitzer for the manufacture of oil
black (Fig. 34) consists of a plate, _A_, with a rim, _a_, fastened to
a vertical axis, _b_. This is carried by bearings in _B_, and is kept
in rotation by the cog-wheels, _d_ and _f_, moved from the shafting,
_O_. The plate is cooled by water supplied by the pipe, _g_, it flows
away by _h_ and the annular vessel, _D_. The lamps, _e_, are connected
with the common oil reservoir by _n_. _H_ is a scraper fastened to _B_
by _x_.