THE DESIGN OF A COLOUR WORKS.
In the establishment of a colour works several conditions are
necessary. The most important is the supply of water in sufficient
quantity and purity. It has already been stated that many pigments
cannot be made with water containing much organic matter or salts,
since the dissolved substances affect the shade. This action not only
takes place in the formation of the colour, but is also unpleasantly
manifest when it is washed. The delicate lakes are discoloured by
organic matter in the water, and are so changed by any considerable
quantity of lime that the alteration in shade is clearly perceptible
after continued treatment. If the water contains but a very small
quantity of iron, the preparation of some pigments is made quite
impossible, since—and this is especially the case with the lakes—the
ferric oxide is precipitated together with the pigment, and in
consequence of its characteristic colour imparts to it an ugly shade.
Thus in choosing a site for a colour works the available water supply
must be carefully examined. If it is not sufficiently pure or in
sufficient quantity, the position must be regarded as unsuitable.
No colour maker, although working on the largest scale, is in a
position to make all the materials he requires. With the continual
development of the chemical industries, the number of these substances
which can be made economically in the colour works continually
diminishes. It is far more advantageous to obtain them from works
in which they are made on the large scale. Many of these substances
are required in large quantity, so that a site should be chosen in
direct communication with the railway, so that the cost of carriage
is diminished, and also the cost of distributing the manufactured
materials. This is especially necessary for materials which have a low
value and consequently can bear no high cost of carriage.
In regard to the space required by a colour works, no actual dimensions
can be given, since these vary with the extent of the business, and
with the pigments produced. In the price lists of large colour works
all the commercial pigments are generally quoted, but they are rarely
if ever actually made in one works, but are obtained at a lower price
from other establishments, which make a speciality of certain pigments,
and by working on a large scale can produce them at such a cost that
the smaller manufacturer is not in a position to compete with them.
Thus there are works in which only white lead or ultramarine is made.
If a colour manufacturer is in the fortunate position of placing his
works on a river, he has not only an unrestricted water supply, but may
also be able to use water power, the cheapest of all powers. When water
power is available, it will be used to raise the large volumes of water
required and to move the machinery for grinding the raw materials,
rasping dye-woods, etc. In a colour works of any size a boiler is
required; if water power is not used, it must be of sufficient power to
give steam for driving the engine, for boiling liquids and for heating
the drying stoves. The boiler is of great advantage in providing steam
for dissolving salts, extracting dye-woods and boiling liquids. When
liquids are boiled by steam there is considerable economy in that the
majority of the boiling tubs can be of wood, which is provided with
a protective coating for liquids which attack wood. Thus there is
economy in dispensing with large metal pans and with the fireplaces
in which they would be built, and also in the course of time there is
considerable saving in fuel.
For a well-equipped colour works a drying stove, in which the pigments
can be thoroughly dried, is important. It is most convenient to heat
drying stoves with steam. The temperature can be easily regulated by
increasing or diminishing the supply of steam. For drying pigments
which would not be injured by considerable increase of temperature, the
drying stove may be heated by a fire.
In a colour works in which many pigments are made sulphuretted hydrogen
is frequently required. Since all lead pigments are blackened by this
gas, the greatest care is required in using it. Also the poisonous
nature of sulphuretted hydrogen is generally under-estimated. In
working with sulphuretted hydrogen, the apparatus depicted in Fig. 3
should be used. It should be placed in a position, such as a closed
yard, in which escaping gas will be harmless. If this cannot be done
the precipitation should be accomplished in closed vessels, from which
a pipe should carry the gas to a fire, where it will be burnt to
sulphur dioxide and water.
In most cases the manufacturer of colours makes but a certain number
of pigments and rarely or never all which are mentioned in his price
lists. The dimensions of the establishment will be in accordance. In
commencing a new colour works it is advisable from purely financial
reasons to produce at first a limited number of colours, but these
in perfection. By many experiments and diligent study of chemistry a
colour manufacturer may hope to compete successfully in so difficult a
branch of chemical technology as the manufacture of colours.