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THE PHOTOGRAPHIC NEWS, Vol. XXVII. No. 1281.—March22, 1883. CONTENTS. PAOE Hyposulphite in Mounts and Paper 177 The Keeping Properties oi Gelatine Emulsion 178 By-the-Bye.—Models 178 The Electric Light in Photography 179 Photo-Lithography, &c. By Major J. Waterhouse, B.S.C 180 Approximative Photometric Measurements 182 Notes 184 Patent Intelligence 186 Twelve Elementary Lessons on Silver Printing 186 PAGE Notes on Photography. By E. Howard Farmer 188 Photo-Lithography. By Thomas M. Laws 188 A Defence of Collodion. By J. F. Coonley..... 190 Photographic Experiences in Egypt. By William H. Bau 190 Correspondence 191 Proceedings of Societies 191 Talk in the Studio 192 To Correspondents 192 The Every-Day Formulary 192 HYPOSULPHITE IN MOUNTS AND PAPER. The most persistent and dangerous enemy of the photo grapher is undoubtedly the ordinary fixing salt, sodium hyposulphite; and the mischief wrought by this salt is especially serious, as it often only sets in after the work has left the hands of the photographer. As old prints become gradually and almost im perceptibly paler and yellower, so does the probability of the holders going to a fresh studio become greater. It is true that the general public have a vague notion that a photograph is not to be relied on as regards permanency ; but the fact that permanent photographs can be produced is also generally known ; and the public, when looking on a fading picture, naturally ask: why does not Mr. So-and- So take his pictures by the permanent method? Much of the rapid fading so common in the present day is rather due to the presence of sodium hyposulphite in the mounts, than to deficient washing of the prints ; although both causes contribute to the general result. The use of chlorine, or of hypochlorous acid, for bleaching paper, is now all but universal; and unless all traces of these agents are effectually removed, the paper becomes brittle and useless. In order to avoid the trouble and expense of a protracted washing, it is usual for the paper-maker to neutralize the destructive tendencies of the chlorine or the hypochlorous acid by the addition of sodium hyposulphite; and as this latter substance is practically harmless from a paper-maker’s point of view, it is by no means unusual for a very considerable propor tion to be added. The hyposulphite thus introduced into the photo grapher’s work-rooms very frequently causes the rapid fading of the prints which he sends out; although there is certain evidence that it is possible for a silver print, which actually contains hyposulphite, to resist the destructive action of time to a really unexpected extent. In such a case, damp appears to be the determining con dition, and the following experiments appear to confirm this view. Prints were mounted with ordinary fresh paste, on mounts well known to be loaded with sodium hypo sulphite, and the mounted pictures were divided into three portions. One set was carefully dried, and exposed to light in a printing frame, a sheet of waxed paper placed at the back serving to keep them from absorbing fresh moisture. The second set was placed loose in a drawer where we keep miscellaneous papers, the room being in general use, and consequently warm and dry. The third set were loosely tied into a bundle, and placed in a damp cellar. At the end of a fortnight the material of the third set showed signs of acidity, when a small piece was cut off and placed on a sheet of delicately tinted litmus paper, this having been previously moistened with water ; while No. 1 and No. 2 did not react on similar pieces of moistened litmus. The acidity was doubtless due to the decomposition or fermentation of the paste, this material having not only been used in mounting the print, but also in manufacturing the cardboard. At the same time, the more delicate half-tones of those portions of the prints which had been preserved in the damp cellar were found to have altogether disappeared; but no difference was noticeable in the case of the first or of the second set. In order to, as far as possible, ascertain whether the presence of hyposulphite was an essential element in the fading, another similar set had been prepared, mounted on cards which were free from the deleterious salt; and por tions of these were placed in the three situations as already described. At the end of the first fortnight no difference at all was traceable between those portions of the second set which had been kept in a damp place, those which had been thoroughly protected from damp, and those which had been kept loosely in a drawer. At the end of six weeks, however, those mounted on card free from hypo., and kept in the cellar, showed very faint indications of fading ; but those which had been mounted on the hypo- sulphited cardboard were by this time almost gone ; large yellowish blotches occupying the greater part of their surface. None of those which had been kept either in printing-frames or in the drawer showed any signs of fading whatever. These results indicate two circumstances as tending materially towards the fading of silver prints—hyposul phite and damp ; the most rapid disappearance of the image taking place when both act conjointly. A source of hyposulphite which is frequently over looked is the white blotting-paper, which is so frequently used for partially drying the prints on their removal from the wash water ; a really notable amount of the salt being frequently present in paper of this kind. We have found that a folio or book, built up of sheets of well washed calico, forms even a better damping-off arrangement than the usual blotting-paper, and its use obviates the necessity of testing each batch of blotting-paper as it is put into stock. When the calico folio becomes dirty or requires washing, it should be unstitched, boiled in clean water, and the separate sheets hung out to dry. The experiments above described indicate the imperative necessity of testing every batch of cardboard for the pre sence of the destructive and mischievous hyposulphite. The testing operation is quite easy, it being merely neces sary to cut up some of the material into small pieces, and to soak the fragments for some ten minutes in the smallest quantity of water which will serve to cover them. The liquid is then drained oft, filtered, and tested as we de scribed in our recent leaders (present vol., page 115 and page 162).