There is, however, a plan of preserving prints on clay, and this is to fasten down the printed portion on a piece of sound paper from the beginning. This is already done to some extent, and it should be universal in the case of isolated plates, but when a book is all printed on clay paper, as many fine and valuable books unfortunately are, it is difficult to say what is best to be done. The only real remedy seems to be a refusal on the part of purchasers to buy such books. But purchasers do not always know when they are buying clay instead of paper. It is, however, not difficult to tell, as the clay-laden paper feels very smooth and soft to the touch of a dry finger. This peculiarity can be easily detected in one or other of the American magazines, Harper’s or Scribner’s, and the difference between the feel of a page holding an impression from a fine half-tone block, and that having only text, will at once be evident. If a mark may be made on a suspected sheet, a drop of water should be put upon one corner, left a second or two, and then dried off with blotting-paper. Now a light scrape with a knife over the damped place will remove a layer of white clay if it is there. There is no doubt that the large majority of our modern books will not be in readable condition in about a hundred years’ time from the date of their publishing. BOOKS TO CONSULT. PAPER. ARTS, SOCIETY OF.--Report on the Deterioration of Paper. _London_, 1898. BLADES, W.--(_Athenæum_, March 30th, 1889, p. 409. Paper on Watermarks). BLANCHET, A.--Essai sur l’histoire des Papier. _Paris_, 1890. BREITKOPF.--Versuch die Einfuhrung des Leinenpapieres. _Leipzig_, 1784-1801. BRIQUET, C. M.--La Legende Paléographique du Papier de Coton. _Genève_, 1884. BRIQUET, C. M.--Recherches sur les Papiers du x^e au XIV^e siècles. _Paris_, 1886. CAMPREDON, E.--Le Papier. _Paris_, 1901. CHARPENTIER, P.--Le Papier. 1890. (Frémy, E.) DUNBAR, J.--Notes on the Manufacture of Wood Pulp Papers. _Leith_, 1892. ERFURT, J.--The Dyeing of Paper Pulp. _London_, 1901. EVANS, L.--Ancient Paper Making. _London_, 1896. GIRARD, A.--Le Papier. _Lille_, 1892. GOODCHILD, G. F., and TWENEY, C. F.--A Technological and Scientific Dictionary. _London._ GRIFFIN, R. B., and LITTLE, A. D.--The Chemistry of Paper Making. _New York_, 1894. HERRING, R.--Paper and Paper Making. _London_, 1855. HOERNLE, A. F. R.--Who was the inventor of Rag Paper? (_Royal Asiatic Society Journal_, October, 1903). HOYER, E.--Die fabrikation des Papiers, 1886. (Bolley, P. A.) KARABACEK, J.--Mittheilungen aus der Sammlung der Papyrus Erz. Rainer. Bd. II., III., 1887. KAY, J.--Paper. _London_, 1893. KLEMM, P.--Handbuch der Papierkunde. _Leipzig_, 1904. LLOYD, E.--Account of a sort of Paper made of Linum Asbestinum found in Wales. (Phil. Trans., Abr. III., p. 105, 1684). MIERZINSKI, S.--Handbuch der Praktischen Papier Fabrikation. _Wien_, 1886. PAYEN, A.--La fabrication du Papier. _Paris_, 1873.