To chrome the pelt first and afterwards to subject it to vegetable tannage is also an obvious possibility, but has not yet been made a commercial success in this country, but has been increasingly used in the U.S.A. during the War. Another typical case of combination tannage is the dongola leather produced by the use of gambier and of alum and salt. This is a vegetable-alum combination, and yields a good quality leather for light uppers, gloves, etc. Goatskins for "glazed dongola" are paddled tanned in gambier liquors, and alum and salt are subsequently added. They are tanned in 24 hours, well washed, and are fat liquored without ageing. The E.I. tanned skins may also be stripped with soda, and retanned in alum and salt, using flour also if desired. Dull dongola are first tawed and then retanned in gambier liquor. "Suède" and "velvet calf" are also tawed and retanned with gambier. Yet another case of combination tannage is that of sheepskins for glacé uppers, which are first tawed thoroughly with alum, salt and flour and dried out for sorting, and are then retanned in chrome by the one-bath process, and finished as usual. Closely related to this is the method of "pickling" in alum and salt and then chrome tanning. Another case is the combined one-bath, two-bath method of chrome tanning. The goods are chromed by a one-bath liquor containing dichromate (say 2 per cent.), and then pass into a reducing bath. There is not much advantage in such procedure, however. From a strictly commercial point of view the "dongola" and "semichrome" leathers have proved the most successful combination tannages, but there seem to be possibilities in combinations of the vegetable tannins with synthetic tanning materials. Many other substances are known to tan, _e.g._ iron salts, cerium salts, sulphur, quinones, fatty acids, the halogens, etc., etc.; hence there is always the possibility that new useful combination tannages may be discovered. REFERENCES. Bennett, "Manufacture of Leather," pp. 243, 374-5. Procter, "Principles of Leather Manufacture," p. 236. SECTION VII.--THE EVOLUTION OF THE LEATHER INDUSTRY The leather trades are amongst the oldest of all industries, but their evolution has been much more rapid during the last two or three decades than at any other period of their history. The European War, moreover, has caused the commencement of another period of rapid development, and it is the aim of this section to point out some of the principal lines of change which have already become apparent.