An examination of the various modes employed for coating Positives, in order to exclude the atmosphere, showed that many of them were not fitted to fulfil the purpose intended. Waxed prints faded quite as much when exposed to moisture as others not waxed. White wax is a substance often adulterated, and Oil of Turpentine has been shown to contain a body resembling Ozone in properties, and possessing the power of bleaching a dilute solution of Sulphate of Indigo. Spirit varnish applied to the surface of the picture after re-sizing with Gelatine was plainly superior to white wax, but nevertheless it did not obviate the fading effect of the moisture upon an unstable Positive which had been toned by sulphuration. Its protective influence is therefore limited. ON THE CHANGE IN COMPOSITION WHICH HYPOSULPHITE OF SODA EXPERIENCES BY USE IN FIXING PAPER PROOFS.[28] [28] These observations are condensed and re-arranged from the papers published by the Author in the 'Photographic Journal' for September and October, 1854. It was remarked by Photographers at an early period that the properties of the Fixing Bath of Hyposulphite of Soda became altered by constant use; that it gradually acquired the power of _darkening_ the colour of the Positive image. This change was at first referred to the accumulation of _Salts of Silver_ in the Bath, and hence directions were given to dissolve a portion of blackened Chloride of Silver in the Hyposulphite in preparing a new solution. Careful experiments performed by the Author convinced him that an error had been entertained; since it was found that the simple solution of Chloride of Silver in Hyposulphite of Soda had no power of yielding the black tones. But it afterwards appeared that if the fixing Bath, containing dissolved Silver Salts, were set aside for a few weeks, a _decomposition_ occurred in it, evidenced by the formation of a black deposit of Sulphuret of Silver; and _then_ it became active in toning the proofs. The presence of this deposit of Sulphuret of Silver indicated that a portion of Hyposulphite of Silver had spontaneously decomposed, and, knowing the products which are generated by the spontaneous decomposition of this salt, a clue to the difficulty was afforded. One atom of Hyposulphite of Silver includes the elements of one of Sulphuret of Silver and one of Sulphuric Acid. Sulphuric Acid in contact with Hyposulphite of Soda produces _Sulphurous Acid_ by a process of displacement; and Plessy has shown that Sulphurous Acid reacts upon an excess of Hyposulphite of Soda, forming two of that interesting series of Sulphur compounds designated by Berzelius the "Polythionic Acids."