In order to ascertain this point, more than six dozen Positives, printed on every variety of paper, were mounted in new and perfectly clean stoppered glass bottles, at the bottom of each of which was placed a little distilled water, to keep the contained air always moist. They were removed at the expiration of three months, having been kept during that time, some in the dark, and others exposed to the light. As the prints were prepared by various methods, toned in different ways, and mounted with or without substances likely to exercise a deleterious action, this series of experiments will possess considerable value in determining some of the intrinsic causes of fading of Positives.[27] [27] For a more detailed account of the experiments, see the original paper in the 'Photographic Journal,' vol. iii. The general results obtained were as follows:--Positives which had been _simply fixed_ in Hyposulphite of Soda remained quite uninjured. Whether developed by Gallic Acid on either of the three Salts of Silver usually employed, or printed by direct action of light, the result was the same. Hence we may infer that the darkened material which forms the image of Photographic Prints does not readily oxidize in a damp atmosphere. _Toned_ Positives were found in many cases to be less permanent than Positives simply fixed. This was especially the case when the toning had been effected by _Sulphur_; all the sulphuretted prints, fixed in solution of Hyposulphite which had been long used, became yellow in the half-tones when exposed to moisture. Positives fixed and toned in Hyposulphite containing Gold were variously affected; some prepared when the solution was in an active state being unchanged, others losing a little half-tone, and others, again, fading badly. These latter were prepared in a Bath which had lost Gold and acquired sulphuretting properties; and it was noticed that they were more injured by the action of boiling water than those Positives which proved to be permanent under the influence of the moisture. Toning by means of Chloride of Gold appeared to be highly satisfactory, but the number of prints operated upon was small. The Sel d'or process also did not injure the integrity of the image, no commencing yellowness or bleaching of half-tones being visible after exposure to the moist air.