han
twelve months, and the sub-committee are inclined to believe that no
book bound in these leathers, exposed on a shelf to sunlight or gas
fumes, can ever be expected to last more than five or six years.
Embossing leather under heavy pressure to imitate a grain has a very
injurious effect, while the shaving of thick skins greatly reduces the
strength of the leather by cutting away the tough fibres of the inner
part of the skin. The use of mineral acids in brightening the colour
of leather, and in the process of dyeing, has a serious effect in
lessening its resistance to decay. A good deal yet remains to be
learned about the relative permanency of the different dyes."

On analysis free sulphuric acid was found to be present in nearly all
bookbinding leather, and it is the opinion of the committee that even
a small quantity of this acid materially lessens the durability of the
leather.

"It has been shown by careful experiment, that even a minute quantity
of sulphuric acid used in the dye bath to liberate the colour is at
once absorbed by the leather, and that no amount of subsequent washing
will remove it. In a very large proportion of cases the decay of
modern sumach-tanned leather has been due to the sulphuric acid used
in the dye bath, and retained in the skin. We have examined very many
samples of leather manufactured and sold specially for bookbinding
purposes, from different factories, bought from different dealers, or
kindly supplied by bookbinders and by librarians, and have found them
to contain, in a large number of cases, free sulphuric acid, from 0.5
up to 1.6 per cent."

The publication of the report should tend to fix a standard for
bookbinding leather. Hitherto there has been no recognised standard.
Bookbinders have selected leather almost entirely by its appearance.
It has now been shown that appearance is no test of durability, and
the mechanical test of tearing the leather is insufficient. Sound
leather should tear with difficulty, and the torn edges should be
fringed with long, silky fibres, and any leather which tears very
easily, and shows short, curled-up fibres at the torn edges, should be
discarded. But though good bookbinding leather will tear with
difficulty, and show long fibres where torn, that is in itself not a
sufficient test; because it has been shown that the leather that is
mechanically the strongest, is not necessarily the most durable and
the best able to resist the adverse influ