air, and so on, gradually oxidise, the great preponderance of iron on
the fibre changing to a kind of iron-rust, corroding the fibres in the
process, and thus at once accounting for the change to the ugly brownish
shade, and to the rubbing off and rapid wearing away of the already too
thin superficial coating of dyed felt fibre. In the final spells of
dyeing in the dye-beck already referred to, tolerably thick with black
precipitate or mud, the application of black to the hat-forms begins, I
fear, to assume at length a too close analogy to another blacking
process closely associated with a pair of brushes and the time-honoured
name of Day & Martin. With that logwood black fibre, anyone could argue
as to a considerable proportion of the dye rubbing, wearing, or washing
off. Thus, then, we have the second cause of the deterioration of the
black, for the colour could not go into the fibre, and so it was chiefly
laid or plastered on. You can also see that a logwood black hat dyer may
well make the boast, and with considerable appearance of truth, that for
the purposes of the English hat manufacturers, logwood black dyeing is
the most appropriate, _i.e._ for the dyeing of highly proofed and stiff
goods, but as to the permanent character of the black colour on those
stiff hats, there you have quite another question. I firmly believe that
in order to get the best results either with logwood black or "aniline
blacks," it is absolutely necessary to have in possession a more
scientific and manageable process of proofing. Such a process is that
invented by F.W. Cheetham (see Lecture VII. p. 66).

In the dyeing of wool and felt with coal-tar colours, it is in many
cases sufficient to add the solution of the colouring matters to the
cold or tepid water of the dye-bath, and, after introducing the woollen
material, to raise the temperature of the bath. The bath is generally
heated to the boiling-point, and kept there for some time. A large
number of these coal-tar colours show a tendency of going so rapidly
and greedily on to the fibre that it is necessary to find means to
restrain them. This is done by adding a certain amount of Glauber's
salts (sulphate of soda), in the solution of which coal-tar colours are
not so soluble as in water alone, and so go more slowly, deliberately,
and thus evenly upon the fibre. It is usually also best to dye in a bath
slightly acid with sulphuric acid, or to add some bisulphate of soda.
There is anothe