Three pairs of books from the library of the Chemical Society were selected, one pair of which was bound in black calf, another in red morocco, and another in green morocco. The bindings of the two books in each pair were of the same age; one binding in each pair did not show deterioration, and the other showed destruction. The ages of the bindings were between 30 and 46 years. These were analysed for the following: pH of water extract before and after dilution, sulphuric acid by both the Procter-Searle and gravimetric methods, oil or grease, and soluble nitrogenous material. From the data, given in tabular form, the following conclusions were drawn. (a) Although bound by the same binder and meant to be bound with the same quality and color of leather, the condition of the two leathers in each of the three pairs and the percentage of sulphuric acid absorbed from the atmosphere are decidedly different, thus suggesting that leathers vary greatly in their power of absorbing sulphuric acid from the atmosphere. (b) Rotted leathers generally contain much more sulphuric acid than sound leathers, although sulphuric acid is apparently not the fundamental factor in the rotting of the red morocco examined. (c) In each of the covers examined the back contained more sulphuric acid than the side, whether sound or rotted. One of the black calf backs, although containing 4.7 per cent sulphuric acid was sound after 46 years. One red morocco back contained 3.2 percent sulphuric acid, yet was sound after 38 years. In almost every case the amount of soluble nitrogen was proportional to the Procter-Searle figure. Whether the grease retarded deterioration or not was difficult to decide, since no information was available as to whether the grease was applied by the manufacturer or later by the librarian, or by handling. A large number of analyses were made of book binding leathers from the Coventry, British Museum, Aberystwyth, Windsor Castle, and Public Record Office libraries. The results suggest that the following factors play a part in the deterioration of leather: (a) sulphuric acid in the leather; (b) sulphuric acid in the atmosphere in which the leather is stored; (c) nature of the tanning material used; (d) condition of the fibers of the leather; (e) grease; (f) degree of tannage. The most important appear to be (c) and (d). All of the rotted leathers showed over 3 percent sulphuric acid. This acid may have been absorbed from the atmosphere either during or after rotting, hence it is not considered safe to assume that the acid caused the rotting. It is deemed possible that rotted leather absorbs acid more rapidly than sound leather. Other examples were found where sound leathers contained over 3 percent of sulphuric acid. The author discusses the conditions under which several of the books were kept in explanation of their condition and the analytical data obtained on them. It is suggested that the quality of the atmosphere has but little effect on the rotting of certain leathers, but considerably accelerates rotting in others. There appears to be very strong evidence that the nature of the tanning material used is a decidedly important factor. Microscopic examination of three pairs of leathers first mentioned in this article showed the fibers of the sound leathers to be well split, and making about a 45 degree angle with the grain. The deteriorated leather showed fibers which were not split up, and tended to run more parallel to the grain. These observations suggest that the treatment of the skin prior to tanning may influence the life of the leather. The following preservative for leather bindings, used in the British Museum for the past 2 years, has given satisfactory results: 11 oz. (fluid) of hexane; 0.5 oz. (avoir.) of beeswax; 1.0 oz. (fluid) of cedarwood oil; and 7 oz. (avoir.) of anhydrous lanolin. -- AATA