in Fig. 25, or three as in
Fig. 26. Besides these, there are winding and beaming and other guide
rollers. Fig. 25 shows the simplest padding machine, where the cloth
passes once through the liquor and through the squeezing rollers. In
Fig. 26 the cloth passes several times through the liquor and twice
through the squeezing rollers, thus ensuring a more perfect impregnation
of the cloth with the dye-liquor, and therefore a more uniform dyeing of
the cloth.

CHAPTER IV.

THE PRINCIPLES AND PRACTICE OF COTTON DYEING.

Students of cotton dyeing should have a good knowledge of the principles
that underlie the processes of dyeing cotton fabrics. It is only by
recognising these principles and then endeavouring to apply them to each
individual case of dyeing, that the dyer or student will obtain a
thorough grasp of his subject. It is the aim of the author to lay down
these principles in a clear and intelligible form. Cotton is dyed in its
loose raw condition, as yarn in the form of hanks, yarn in the form of
cops, and in the woven pieces of every kind. Formerly the idea was
prevalent among cotton dyers that the process which succeeds with piece
goods would not answer with yarns. It is now recognised however that
this is not so, that a process which will dye cotton yarn will also dye
cotton piece goods or loose cotton. The differences which do exist in
the practical working of the processes entirely arise from the
difference in the form in which the cotton is presented to the dyer, for
it must be obvious to any one that the mode of handling a piece of
cotton cloth during the time it is in the dye-bath must be different
from that of a hank of yarn, a parcel of loose cotton or a number of
cops. The various machines used for dyeing all these forms and the
manner of working them have been already described.

The dyes, whether natural--derived from the various dye-woods, etc.--or
artificial--prepared from coal tar--may according to their varied
chemical composition and constitution be divided into seventeen or
eighteen distinct groups, but it is not intended here to give any
account of them; the reader is referred to other books such as _The
Dictionary of Coal Tar Colours_, by George H. Hurst; _The Chemistry of
Coal Tar Colours_, by Benedikt and Knecht; or _The Chemistry of Organic
Colouring Matters_, by Nietzki, where the composition and properties of
the dyes are fully described.

From the manner in which the various