BLACKS.
All the black pigments in use owe their colour to carbon, and all are
produced by artificial means, no natural form of carbon possessing the
requisite qualities.
Several manufactured carbonaceous substances are known in commerce
under the generic name of “Blacks.” The most important of these are
animal-black, bone-black, Frankfort-black, ivory-black, and lamp-black.
They are usually obtained by carbonising organic matter, particularly
bones, in closed vessels or crucibles, or by collecting the soot formed
by the combustion of oily, resinous, and bituminous substances. Other
blacks than those enumerated are manufactured, but only on so small a
scale as to be of no commercial importance.
Carbon, lamp, and vegetable blacks consist almost entirely of carbon,
containing usually from 98 to 99½ per cent. of that substance, the
residue consisting of a little ash, water, and occasionally unburnt
oil. Bone and ivory blacks, on the other hand, are chiefly composed of
mineral matter, which may amount to 65 or 75 per cent. and is mainly
represented by phosphate of lime. Their actual colouring matter, the
carbon, only constitutes 15 to 30 per cent. of the mass. The balance is
water and unburnt animal tissue. Blacks prepared from animal matters
other than bone and ivory carry 40 to 80 per cent. of carbon, and their
mineral matter is generally in the form of carbonates of lime and of
the alkalies.
The principal impurity to be watchful of in the vegetable and lamp
blacks is a small quantity of oily matter which may seriously
interfere with their drying qualities. They should leave very
little ash after being burned in a crucible. Bone and ivory blacks
are sometimes valued as much for their mineral matter as for their
colouring matter. The proportion of this mineral matter is ascertained
by heating a certain weight of the black to red heat in a crucible till
every trace of black has disappeared, and then weighing the residue.
The residue should next be boiled in strong hydrochloric acid till
it is dissolved; if there is any which will not dissolve it is most
probably barytes, which has been added as an adulterant and to make
the black weigh heavy. When the solution is complete, the addition
of ammonia will throw down a precipitate of phosphate of lime, which
should equal 60 to 70 per cent. of the original weight of mineral
matter. If much less than this, it is likely that whiting or gypsum
has been mixed with the pigment. As carbon is not acted upon by acids
or alkalies, it follows that all pure carbon blacks are in themselves
perfectly stable and permanent pigments, and that they exert no
influence on other pigments with which they may be mixed.
=Animal-black.=--This substance is almost identical with bone-black,
but is generally in a more finely divided state. Any animal refuse
matter may be used in its preparation, such as albumen, gelatine, horn
shavings, &c. These are subjected to dry distillation in an earthenware
retort. An inflammable gas is given off, together with much oily
matter, ammonia, and water, while a black carbonaceous mass is left
behind. This is washed with water and powdered in a mill, the product
being animal-black. It is largely used in the manufacture of paint,
printing ink, and blacking.
=Bone-black.=--When bones are heated in a retort or crucible, the
organic constituents are decomposed and carbonised. A mixture of
combustible gases is given off; some of these do not condense on
cooling, others condense in the form of a heavy oil, called bone-oil.
Also much water containing tarry water and ammoniacal salts in solution
passes over. The residue in the retort or crucible consists of finely
divided carbon, in intimate mixture with the inorganic constituents
of the bones: this mixture constitutes ordinary bone-black, or animal
charcoal, as it is sometimes called. The inorganic portion may, if
required, be removed by washing the residue in dilute hydrochloric acid.
The process, as worked on the large scale, is carried on in different
ways, according as it is desired to collect the volatile condensable
portion of the distillate, or to allow it to escape. In the latter
case, when it is required to obtain only bone-black, the apparatus
employed is of a very simple nature, and the amount of fuel needed
is comparatively small. The carbonisation is effected in fire-clay
crucibles, 16 in. high and 12 in. diameter. These are to be preferred
to crucibles made of iron, which were much used at one time, since they
do not lose their round form when subjected to a high temperature; in
consequence of this, they fit more closely together in the furnace,
less air can penetrate, and therefore less of the charcoal is consumed
by oxidation. The furnace is an ordinary flat hearth, having a
superficial area of about 40 square yards, and is covered in with a
flat arch, all of brickwork. The fireplace is situate in the middle of
the hearth; the crucibles are introduced through doors in the front,
which are bricked up when the furnace is filled; each furnace holds
eighteen crucibles. The crucibles, filled with the coarsely broken
bones, are covered with a lid luted on with clay. To economise fuel,
the furnaces should be in a row, and placed back to back.
The arrangement of the furnace and pots is shown in Figs. 1 and 2. A is
the fireplace; B, the crucibles, eighteen in number, spread over the
floor of the furnace in a single layer; _c_, _d_, _e_, and _f_ are the
flues for conducting away the heated gases arising from the calcination
of the bones, as well as the waste heat itself; the last portion of the
flue is fitted with a damper _g_. The furnaces are intended to be built
in fours, back to back, the waste heat serving in a great measure to
conduct the operation of the revivifying apparatus placed in the centre
of the group, and marked C.
[Illustration: Figs. 1 and 2.--BONE-BLACK FURNACE.]
When the furnace is filled and the doors are bricked up, the heat is
slowly raised to redness, at which point it is kept for six or eight
hours. The combustible gases are evolved and consumed in the furnace
as the bones begin to decompose, and by this means so much heat is
produced that only a small quantity of fuel is needed to maintain the
required temperature. When the carbonisation is complete, the doors are
taken down and the crucibles are removed to cool, their places being
immediately filled with fresh ones. The heat must be kept as uniform
as possible throughout the process: if it be not sufficiently high,
the bone-black will contain a portion of undecomposed organic matter,
which renders it quite unfit for use; if, on the other hand, the
temperature be raised too high, the bone-black will become dense and
compact, whereby its efficacy as a decoloriser is much reduced. When
the charcoal in the crucible has become perfectly cool, it is removed
and crushed. When required for decolorising or deodorising purposes, it
is only roughly broken up into small lumps, in which form it is most
readily applicable. The crushing is effected by means of two grooved
cylinders, consisting of toothed discs, alternately 10 and 12 in. in
diameter. These are so placed that the 10-in. discs of one cylinder are
opposite the 12-in. discs of the other, and thus, in revolving, the
carbonised bones are crushed to fragments between them, but are not
reduced to powder. They are passed successively through six of these
mills, the cylinders of each couple being nearer to each other than
the last. Finally the crushed bones are carefully sieved; the powder
is placed apart from the lumps, again passed through finer sieves, and
sorted out into different sizes.
A furnace such as that described above will carbonise four charges of
bones in one day, each charge being more than half a ton in weight.
With careful work, the bones will yield 60 per cent. of bone-black, or
more than one ton daily.
If it be required to condense the volatile gaseous products of the
carbonisation, this process is conducted in retorts similar to those
used in the manufacture of acetic acid from wood: these are so arranged
that the whole of the gaseous products are condensed and collected.
The aqueous portion of the distillate is usually evaporated down to
obtain salts of ammonia; the uncondensable gases may be employed for
illuminating purposes. The manufacture of bone-black is usually carried
on in the neighbourhood of large towns, where a good supply of bones
may be readily obtained.
Ordinary bone-black has about the following composition: Phosphate and
carbonate of lime, and sulphide or oxide of iron, 88 parts; charcoal,
containing a small quantity of nitrogenous matter, 10 parts; silicated
carbide of iron, 2 parts. The decolorising properties of bone-black are
due solely to the presence of the charcoal.
When intended for use as a deodoriser or decoloriser, bone-black should
be kept carefully excluded from the air, for by exposure it loses this
power to a great extent, and becomes almost inert. That which has been
freshly burned is therefore best for these purposes.
The cost of production of bone-black may be calculated as follows:--
£ _s._ _d._
4 tons fat bones at 4_s._
per cwt 16 0 0
27½ bushels coals 1 3 9
2 firemen 0 4 9
4 workmen 0 8 0
1 carman 0 2 4
2 horses 0 5 7
Breaking up the bones 1 5 4
Rent and taxes 0 8 0
Interest, repairs, and
wear and tear 0 7 2
Contingencies and transports 0 2 4
-------------
£20 7 3
Produce:--
Black, 60 per cent., say 38 cwt. in grains, at
14_s._ 3_d._ 13 10 9
10 cwt. fine, at 5_s._ 6_d._ 1 7 8
Fat, 6 per cent., say 5 cwt., at 31_s._ 8_d._ 7 18 4
---------
£22 16 9 22 16 9
--------
Profit £2 9 6
Bone-black never has the depth or brilliancy of lamp-black, but it
mixes well with either water or oil, and though a slow drier as an oil
paint, is permanent and not high priced.
=Frankfort-black or Drop-black.=--This is a black powder obtained
from dried vine-twigs carbonised to a full black and then ground very
fine. On a large scale it is prepared from a mixture of vine-twigs,
wine-lees, peach-stones, bone-shavings, and ivory refuse. It varies
in shade according as the animal or vegetable charcoal is in excess;
when the latter predominates, the powder is of a bluish colour; but
when there is an excess of animal charcoal, it has a brownish tinge.
It is customary to wash the powder well when first made, in order to
remove any soluble inorganic impurities. The finest Frankfort-black
is probably the soot obtained from the combustion of the materials
mentioned above. It makes an excellent pigment, and is extensively used
by copperplate engravers in the preparation of their ink. Drop-black
is simply Frankfort-black ground exceedingly fine, mixed with a little
glue water, and dried in pear-shaped drops for sale.
=Ivory-black.=--Ivory-black is a beautiful black pigment prepared by
carbonising waste fragments and turnings of ivory. These are exposed
to a red heat for some hours in crucibles, great care being taken
to avoid overheating or burning. When quite cold, the crucibles are
opened, and the contents are pulverised, the richest coloured fragments
being kept apart for the best quality. The powder is then levigated
on a porphyry slab, washed well with hot water on a filter, and dried
in an oven at a temperature not exceeding 212° F. The product is of a
very beautiful velvety black colour, superior even to that obtained
from peach-kernels, and quite free from the reddish tinge which so
often characterises bone-black. Ivory-black, like Frankfort-black, is
employed by copperplate printers in the preparation of their ink. Mixed
with white lead, it affords a rich pearl-grey pigment.
=Lamp-black.=--Lamp-black is an exceedingly light, dull-black powder,
formed by the imperfect combustion of oils, fats, resins, &c. It may
be prepared on a small scale by suspending a small tin-plate funnel
over the flame of a lamp fed with oil, tallow, or crude naphtha, the
wick being so arranged that it shall burn with a large and smoky flame.
Dense masses of this light carbonaceous matter gradually collect in
the funnel, and may be removed from time to time. The funnel should be
furnished with a metal tube to convey the gases away from the room, but
no solder must be used in making the connections.
[Illustration: Figs. 3 and 4.--APPARATUS FOR MAKING
LAMP-BLACK.]
An especially fine quality of lamp-black is obtained from bone-oil,
deprived of the ammonia with which it is always contaminated. It is
manufactured on a commercial scale by means of the apparatus shown
in Figs. 3 and 4. The oil is contained in the lamp A and kept at a
constant level by means of the globular vessel B, which is also filled
with oil and inverted over A. The oil flows from the lamp into the
tube C, which is bent upwards at the farther extremity on a level with
the oil in the lamp. A cotton wick is supplied to the bent end of the
tube, as well as a little spout D, for conducting away any oil that
may overflow into the receptacle E placed beneath. A conical hood _a_
surrounds the flame of the lamp and terminates in a tube _b_, through
which are conveyed the sooty products of the combustion of the oil into
the wide lateral tube _c_, arranged to accommodate the smoke from about
a dozen such lamps placed at intervals of about 6 feet, as indicated in
the figures. The effect of this wide tube _c_ is not only to cool the
smoke, but also to collect the water and other liquids condensed. The
smoke and vapours pass hence into _d_, the first of a series of sacks
made of closely woven linen, about 10 or 12 feet long and 3 feet in
diameter, closed at the bottom with a trap or slide _e_, and formed at
the upper and lower ends of sheet-copper tubing made funnel-shaped. The
upper one of these is prolonged into an additional pipe _f_, by means
of which the smoke arrives at the second sack _g_ in the series, thence
finding its way to the third, and so on till the last sack of the row
is reached. In connection with the last sack of each row is placed a
horizontal flue F, in which are arranged frames covered with wire gauze
and mounted on hinges. Their purpose is to retain the small remaining
portions of lamp-black passing out with the smoke from the sacks. The
meshes of the gauze are constantly getting filled up with soot, which
necessitates a periodical checking of the draught for its removal. This
is done by means of the rod G, which, when raised and allowed to fall
suddenly, jerks the accumulated mass off the gauze. The current of
air passing through the entire apparatus can be regulated by a damper
placed at the entrance to the chimney in which the flue F embouches.
At regular intervals, the mouthpieces in the lower ends of the sacks
are removed, and their contents are shaken out separately and collected
according to their various qualities. That gathered from the first sack
in each row should always be kept apart from the remainder, as it is
much contaminated by the presence of resinous and tarry matters.
[Illustration: Fig. 5.--APPARATUS FOR MAKING LAMP-BLACK.]
The old-fashioned method of preparing lamp-black from the incomplete
combustion of gas tar is conducted in an apparatus resembling that
shown in Fig. 5. The furnace _a_, lined with fire-brick, contains a
kettle _b_, and is surmounted by a large thick cast-iron hood _c_,
communicating with a stone or brick condensing chamber, divided
by means of perforated partition walls into three unequal sized
compartments _d_, _e_, _f_, wherein the black is deposited. A chimney
_g_ delivers uncondensed vapours into the atmosphere. In working, the
furnace is first brought to a red heat, then the kettle _b_, charged
with tar, is introduced. As a charge is finished, more tar is added,
with occasional stirring, till the kettle becomes inconveniently full
of residue, when it is withdrawn and a fresh one replaces it. The
residue is chipped out and used as fuel. The black is removed weekly
through the door _h_. It is of good quality and colour so long as the
combustion is conducted with a minimum of air, admission of which is
controlled at the furnace. The yield is about 25 per cent. of the
weight of the tar; and one furnace should treat a ton of tar in a week.
One workman can manage several furnaces.
An improved process has been introduced by Martin and Grafton for the
preparation of lamp-black from coal-tar, which affords a very good
product. The coal-tar is first stirred up energetically with lime-water
in any convenient vessel, after which the mixture is allowed to stand
until the coal-tar has subsided to the bottom, when the lime-water is
drawn off. The tar is then well washed by decantation with hot water,
and rectified in the ordinary naphtha still. Afterwards it is run into
a long iron cylinder, which is placed over a furnace, and supplied
with numerous large burners. Each burner has a metal funnel placed
immediately above it, connected with a cast-iron pipe, into which all
the fumes from each burner are conducted. The naphtha in the cylinder
is heated almost to the boiling point by the furnace beneath. A series
of smaller pipes lead away the fumes from the main pipe into a row of
chambers, and thence into a series of large canvas bags, placed side
by side, and connected alternately at top and bottom. The bags vary
in number from fifty to eighty, the last one being left open to allow
the smoke to escape, after traversing some 400 yards since leaving the
burners. The best quality of lamp-black is found in the last bags, that
near the furnace being much coarser and less pure. The bags are emptied
whenever they contain a sufficient quantity.
The process employed in Germany for the manufacture of lamp-black is
to conduct the products of the combustion of any resinous matter in a
furnace into a long flue, at the end of which is placed a loose hood,
made of some woollen material, and suspended by a rope and pulley. The
lamp-black collects in this hood, and, when a sufficient quantity has
accumulated, is shaken down and removed. In this manner about 6 cwt. of
lamp-black may be collected in twenty-four hours.
One form of the apparatus is shown in Fig. 6. The circular structure
_a_ is lined inside with hanging cloths upon which the black can
condense, and is covered with a conical roof from which depends a
movable sheet-iron cone _b_, perforated at its apex to give egress to a
current of air. This cone _b_ is supported by a rope _g_ passing over a
pulley _c_ and accessible from the outside. A fireplace _d_, containing
a small iron dish _e_ for holding the resin, is built against one of
the side walls of the structure in such a manner that it can be fired
externally. The rate of combustion is regulated by a small sliding
damper on the door of the fireplace. When the black has accumulated in
the chamber _a_ to such an extent that operations must be suspended,
the fire is let out, and the chamber is left to cool entirely, so that
the black may not ignite on contact with the air. The cone _b_ is then
lowered, and in its descent scrapes the walls of the chamber _a_ and
causes the black to collect on the floor, whence it is removed through
an iron door _f_ which at other times is kept tightly luted.
[Illustration: Fig. 6.--APPARATUS FOR MAKING LAMP-BLACK.]
In England, an inferior variety is sometimes obtained from the flues of
coke-ovens. That known as _Russian lamp-black_ is made by burning chips
of resinous deal or pine wood, and collecting the soot formed; but it
is objectionable, owing to its liability to take fire spontaneously
when left for a long time moistened with oil.
A modified form of apparatus has been introduced by Thalwitzer, a
German manufacturer, and is shown in Figs. 7 and 8. A vertical tube is
provided at its upper end with a funnel, into which cooling water is
poured and flows out through openings in the tube immediately above a
circular plate of thin cast or wrought iron arranged horizontally and
[Illustration: Figs. 7 and 8.--THALWITZER’S LAMP-BLACK
APPARATUS.]
secured at its centre to the tube. Round the periphery of this plate
is a vertical rim of tin plate, at the top of which is a pipe through
which the cooling water runs into a gutter round the top of the
cylindrical casing, the water being carried off from this gutter by
a pipe. The vertical tube is carried near its upper end in a bearing,
and at that part is attached a worm-wheel geared into it by a worm
driven by any suitable power. At the underside of the circular plate is
fixed a scraper, the edge of which is formed with a strip of leather in
contact with the lower surface of the plate. Opposite the scraper, at
the bottom of the casing, is a burning lamp, which sucks up the oil for
its consumption by a flat wide wick.
The operation is as follows:--The vertical tube is caused to revolve
by the action of the worm-wheel, the circular plate thereby receiving
a slow rotary movement; and a small stream of water being poured into
the funnel at the top of the tube, this water passes down the latter
and through the openings on to the circular plate, which is thus kept
cool. The burning lamp filled with paraffin or other oil is brought as
near to the circular plate as is necessary for the cooling of the flame
and the most perfect extraction of the carbon, which, in the form of
soot, attaches itself readily to the plate, owing to its coldness and
to the condensation of the steam produced. The revolving plate presents
continually to the flames a new and clean surface, in consequence of
the lamp-black being scraped away by the scraper as soon as deposited,
and brought away through a pipe or shoot into a collecting barrel.
The apparatus as shown in Figs. 7 and 8 consists of a round metal
plate A, provided with a flange _a_, and fixed on a vertical shaft _b_
supported by the bearing B, and carrying at its upper end a worm wheel
_d_ set in motion by a worm. The plate A is cooled by water admitted
through a pipe _g_, and the flange _a_ is provided with a discharge
pipe _h_, through which the cooling water runs into the groove D,
surrounding the whole apparatus. Underneath the plate A a number of
lamps J are applied, which are fed with oil by a common pipe _l_. H is
an oblique scratcher or blade, the working edge of which is formed by a
strip of leather, and touches the lower surface of the plate A.
For manufacturing lamp-black, a slow rotary motion is imparted to the
apparatus by means of the worm and worm-wheel, and a slight current
of water is directed upon the plate A through the pipe _g_. The lamps
J, filled with paraffin oil derived from lignite, or with any other
suitable oil, are ignited and approached to the plate A as far as
is necessary for cooling the flame, so as to deposit the greatest
possible quantity of black. The latter adheres to the cold surface of
the plate, which is also kept damp by the aqueous vapour formed during
the combustion. The revolution of the plate serves to bring the flame
continually into contact with new and clean portions of the plate, the
black being continually scraped off by the blade or scraper placed
opposite the flames, and conducted through a channel into a collecting
trough.
There is a risk of overburning, causing a grey tint and a hard and
granular texture.
A variety of lamp-black known as “carbon black” or “gas black,” has
of late years assumed an important position among black pigments. It
is produced in considerable quantities in the United States by the
combustion of the natural gas issuing from the earth in the mineral oil
regions. The soot arising from the imperfect combustion of the gaseous
hydrocarbon is made to deposit itself on cooled iron surfaces. These at
first were made stationary, but now take the form of revolving discs or
cylinders, which are automatically cleansed of the black as fast as it
is deposited. This type of lamp-black is remarkably free from mineral
impurities and unburned oil, and of a full colour.
An improved lamp-black kiln has been introduced in which the use of
water is dispensed with. It is shown in Figs. 9 and 10. The furnace A,
which is preferably built double, as shown, is constructed of brick
lined with firebrick, with a rear wall _a_ that divides the furnace
room from the condensing room, side walls _b_, front _c_, and central
dividing wall _d_, that divides the furnace into two long and narrow
fire
[Illustration: Figs. 9 and 10.--AMERICAN LAMP-BLACK KILN.]
spaces. The bottom of the fire spaces _e_ is formed by a sheet iron
plate _f_ that is supported by the walls, and the space below plate _f_
serves as an air space through which air circulates by openings _g_
in the front and side walls, this circulation of air tending to keep
the plate _f_ cool. The rear of the fire space _e_ extends upward and
communicates by an opening _h_ through the wall with the condensing
room. In the front wall _c_ is an opening to each fire space _e_ and
a door _i_ to each opening. The oil or other liquid is supplied by
pipes _k_ that enter from the outside near the rear of the fire spaces.
The outer end of each pipe _k_ is fitted with a cup-shaped receptacle
_l_, into which the oil will run from the vertical branch of the main
supply pipe _m_, so that the amount of oil running into each pipe
_k_ may be observed, and regulated by a cock. The pipe _m_ feeds the
oil to one or more furnaces, the supply of material to each furnace
being separately regulated. In the fire spaces beneath pipes _k_ are
placed shallow cast iron drip pans _o_ to receive the oil, and the oil
running in faster than it will burn will drop while on fire into the
pans _o_, and be spattered into small particles. These pans are changed
frequently, access to them being obtained by doors _i_. A slide _p_ is
provided in each door _i_ to allow of ventilation when required. The
slides and doors should close air-tight. By constructing the fire space
_e_ long and narrow, the plate _f_ is more readily kept cool, and the
space in front of the point of combustion renders the smoke less liable
to escape by the doors. The products of combustion pass through the
opening _h_ to the condensing room, which is lathed and plastered, and
if the room is sufficiently large a number of furnaces may be fitted to
discharge into the same room. This furnace is especially adapted for
burning dead oil; but by using burners of suitable construction other
oils may be burned, and a superior quality of lamp-black made from
mitigated spirits.
A very large proportion of the lamp-black now made is derived from the
combustion of creosote or anthracene oils from coal tar, or of the
residues of shale-oil distillation. The form of combustion chamber
varies in different works, but is typified by the following rough
sketch of that in use at the Stampshaw Chemical Works (Fig. 11).
[Illustration: Fig. 11.--_Apparatus for making Lamp-black from Creosote
or Shale Oil._]
At these works a horizontal brick flue _a_ about 18 inches square and
about 10 feet long is provided. At one end it enters the black-house
_b_, and is here provided with a damper _c_ to shut it off when not
working. The other end opens to the air, and here is a sliding door
_d_ which, when shut down, leaves an opening round a small pipe _e_,
which enters in this situation from a main pipe that conveys oil in a
similar manner to four burners of this description placed side by side.
At the bottom of the flue is an iron tray _f_ to catch any liquid that
falls from the tube, and in this tray the oil is burned. The burning of
oil in one of these flues is not allowed to go on for more than three
hours, and, when the combustion is over, the communication with the
black-house is closed, the entrance door of the flue is opened, and the
cover is taken off the chimney _g_ so that the flue may become cooled,
and another flue is taken into use.
The black-house is a brick chamber into which the smoke passes, and
where it deposits its sooty particles. In some works there is only
one undivided chamber; in other works there are more than one, and
the chambers communicate by flues through which the smoke passes from
one to another. At other works the chamber is divided by vertical
partitions, springing alternately from the two ends, so as to
constitute one high zigzag flue, along which the smoke must travel
to its outlet from the black-house. This chamber must needs have an
opening somewhere to the outer air. The opening is sometimes a small
chimney in the roof, and sometimes a short louvre tower. This is
necessary to produce a trifling draught, just enough to carry the smoke
into the chamber and no more.
In some works, the black from the black-house is also calcined, the
object of the “calcination” being to get rid of all greasiness, a point
of great importance when the lamp-black is to be used for making fine
pigment. This process is conducted in circular iron pans, usually about
2¼ feet high and 2¼ feet diameter, which are provided with removable
iron covers. A pan of this size will hold about 2 lb. of lamp-black. A
bowlful is first put in and lighted by a red-hot iron; more and more is
added from time to time as the ignition proceeds. When the pan, being
full, leaves off smoking, the calcination is known to be complete, and
the pan is then covered and its contents are allowed to cool. The loss
undergone in this process is about 25 per cent. The smoke which comes
off is acrid and very irritating to the eyes, like that proceeding from
boiling oil, and it is difficult for a person unaccustomed to it to
remain many minutes in the chamber where calcining is going on. This
process is sometimes conducted within a chamber, but frequently under a
shed or even in a building freely open to the air.
There are three sources from which nuisance may arise in lamp-black
making: 1. The smoke which issues from the chimney of the black-house,
small as it sometimes is, often constitutes a nuisance to near
neighbours; but the nuisance is not a very serious one, and it does not
extend very far from the works, never to a greater distance than about
50 yards. The odour, even when but little smoke escapes, is oppressive
and suffocating in character, and resembles that diffused in a room
by a smoking table-lamp. It occasions headache, but is not otherwise
injurious to health. 2. A similar nuisance of suffocating smoke
sometimes proceeds from the burners, but this is when they are leaky or
when there is a deficiency of draught through the black-house, or when
the doors of the burning chambers do not shut closely, and when there
is much wind blowing past them. This nuisance chiefly occurs when the
burners are open to the air and merely protected by an open shed. 3.
The escape of acrolein and other offensive vapours from the calcining
house.
The best mode of preventing nuisance from the black-house is so to
elongate the chamber as to give abundant opportunity for the soot to
deposit in the course of the smoke along it to the outlet, and by
taking means to consume by fire what little smoke escapes deposition. A
most effectual arrangement for the accomplishment of these ends is to
have a black-house 150 feet long, and so divided by partitions within
as to cause the smoke to traverse a distance of altogether 500 feet
before it finds an exit; the exit from the chamber communicating with a
fire, in which the last of the smoke is consumed, and which serves to
assist in regulating the draught through the chamber.
The regulation of the draught through the burner and black chamber is
of importance in order to avoid the escape of smoke from the burners.
If the draught be too great, too much black is lost from the chamber,
but if, on the other hand, it be too little, the smoke instead of
passing into the chamber will come out into the works and create a
nuisance, especially where the burners are erected in the open air,
under circumstances in which variation in the force of the wind cannot
fail to interfere with due regulation of draught. This part of the
manufacture should be conducted within a building of some sort.
The best mode of preventing nuisance from calcination is in operation
at Shackell & Edwards’ works, in Hornsey Road, Islington. At these
works the black is calcined in a chamber 20 feet square and 25 feet
in greatest height, with a paved floor and arched roof. In the centre
of the roof is the opening where a fire was formerly placed, but which
is now closed by a sky-light, capable of being raised. The calcining
pots are ranged round this chamber, and a fan, employed to draw off
the vapours from the oil-boiling pans, is further utilised to draw off
also, from the upper part of the calcining-house, the vapours arising
from the calcination, and to drive them into the boiler fire, where
they are consumed. Calcination should always be conducted in a closed
building duly ventilated so as not to create nuisance.
The transport of lamp-black is effected in barrels or bags; when in the
latter, these should be previously soaked in water containing some clay
in suspension, which stops up the pores of the sacking, and thereby
prevents loss.
The particular virtue of lamp-black as a pigment lies in its state
of extremely fine division, which could not possibly be attained by
artificial means; this quality renders it invaluable as the basis of
black pigments, all of which contain it in a greater or less quantity.
Indian ink and printers’ ink are also composed principally of this
substance.
=Unimportant Blacks.=--In addition to the recognised blacks already
noticed there are a number of other sources of black pigment which
have been drawn upon to a limited extent, or have been suggested
as substitutes for the standard articles. They only merit a short
description.
_Aniline black_ is prepared by adding an acidified (sulphuric) solution
of bichromate of potash to an aqueous solution of hydrochlorate of
aniline, and washing the precipitate. The cost is prohibitive.
_Candle black_ is candle smoke condensed on a cold plate.
_Charcoal black_ is finely-ground wood charcoal.
_Coal black_ has been suggested by grinding coal, but lacks the
requisite qualities of a pigment.
_Cork black_ is a very fine pigment prepared by calcining cork refuse.
Limited supply.
_German black_ is Frankfort black.
_Iron black_ is ground black sulphide of iron.
_Lead black_ is prepared by boiling lead fume in sulphide of soda
solution. It would probably be unstable on account of oxidation.
_Manganese black_ is ground oxide of manganese. It is costly, and dries
too quickly.
_Prussian black_ is calcined Prussian blue. It is not of a good colour,
nor economical.
_Prussiate black_ is the carbonaceous residue from making yellow
prussiate of potash. Used chiefly for decolorising syrups, &c.
_Spanish black_ is cork black.
_Tannin black_ is proposed to be made by exhausting the tannin from
refuse leather and tanning agents, and adding alum and sulphate of
iron. The colour is blue-black, weak, and unstable.