=337.= The principal leathers used for public library bindings are pig-skin, persian and levant moroccos, and roan. Calf, russia and other fancy leathers should not be used, as they turn brittle under the influence of heated and dry air, and crumble to pieces. Apart from this, they are costly and otherwise unsuitable for public library purposes. The leathers recommended should be used according to the books which they have to cover, and the following list will give an idea of the best classes for which to use each kind:-- Levant morocco, or real morocco, made from goat-skin. This material should be used for very valuable books which require a handsome and dignified binding. It is very durable, but expensive for ordinary work. Persian morocco, made from sheep-skin, is not so dear or so good as levant morocco, but is a durable and satisfactory leather if a good quality is procured. It should be used for popular books in the non-fictional classes of the lending department. Heavy books can be bound in this leather, but pig-skin is better. The more it is handled the better it wears and keeps its condition. Roan is a kind of inferior sheep-skin, with a different grain and surface from Persian morocco, and is a useful and cheap leather for certain classes of books, such as the less popular works of travel, science, theology, fiction, etc. Books up to the crown octavo size can be half-bound in this material at prices ranging from 1s. 6d. to 2s. a volume. Heavy books are not recommended for binding in this leather. Pig-skin is the strongest leather of all, and also the most durable for much-used heavy books; but librarians should make certain that real pig-skin is supplied, and not some wretched imitation. The price of pig-skin is rather more than good Persian morocco. All reference works, such as dictionaries, atlases, directories, and other volumes which are being constantly handled, may well be bound in this. All leathers specified for bookbinding should be of the acid-free description recommended by the Society of Arts Committee (1898-1900) and the Sound Leather Committee of the Library Association. Sumach-tanned leathers are now to be had with a special guarantee from the makers.