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THE PHOTOGRAPHIC NEWS. Vol. XII. No. 515.—July 17, 1858. CONTENTS. PAE Prevention of Stains on Negatives in Hot Weather 337 Sensitive Albuminized Paper Preserved Ready for Use 337 Recovery from Cyanide Poisoning 338 The Coffee Dry Process 338 Pictorial Effect in Photography. By II. P. Robinson 339 Photo-zincography in Practice. By J. Waterhouse, R. A 340 On the Principles of Lighting and of Constructing Studios. By Dr. II. Vogel 342 On the Action of Bromine upon certain Ethers. By MM. A. Ladenberg and II. Wichelhaus 343 PAGE An Easy Mode of Obtaining the Position and Focus for Field Views. By W. Campbell 344 New Red Colouring Matter 344 Scientific Gleanings 345 Correspondence—Informers and Piracy— Mr. Bovey’s Mode of Toning—Landscape Backgrounds to Portraits 345 Talk in the Studio 346 To Correspondents 347 Registration of Photographs 348 PREVENTION OF STAINS ON NEGATIVES IN HOT WEATHER. The recent hot weather has brought into operation the train of summer difficulties with which photographers are familiar. Matt silver stains and other markings—the result of the silver solution drying or concentrating on the film if the plate be kept more than a few minutes before developing—pinholes, and similar troubles, have been pre valent, as we learn from the letters of many correspon dents. We do not intend here to enter into a re-discus sion of the various remedies which have been proposed and tried with more or less of success. For information on almost every form of the defects in question, and for details of the various remedies, we must refer our readers to many articles published in our previous volumes. We wish now to call attention to the practical working of one of the remedies for matt silver and other stains, which we recently saw in very efficient operation in the establishment of Mr. Hughes, at Ryde. The remedy in question consisted in washing the excited plate in distilled water as soon as it was removed from the nitrate bath. This, it will be said, is not new ; and the observation will be unquestionably true. The novelty and the especial effi ciency consist in a very small item in the operations. When a plate has been washed in this way it is necessary to restore the free nitrate which has been removed to aid in the operation of developing. 'Two or three modes of effecting this have been tried. One method consisted in adding a little free nitrate to the developer. The disadvan tage of this method was a tendency to irregular and patchy development; and unless the plate had received consider ably longer exposure than it would have required when unwashed, a hard, under-exposed negative has been the re sult. A more even development has been secured when the plate has been covered with a little of the nitrate soln- ion previous to applying the developer, and a better result still when the plate has received a momentary redip in the nitrate bath prior to development. But still it has been found that an unusually prolonged exposura was necessary to secure a good negative, and an impression has prevailed that a washed plate was less sensitive than a wet plate in its normal condition. That this impression is erroneous we have recently had opportunity of proving satisfactorily. The whole secret of success depends on the time the plate is permitted to remain in the bath on redipping : sufficient time is necessary to permit the film to become thoroughly permeated again by the nitrate solution. It seems that each atom of impressed bromo-iodide of silverrequiresthecontact of free nitrate of silver in order that the proper reduction may be completed by the developer. The plate which, re ceiving only a momentary redip sufficient to cover its sur face with the silver solution, would yield a thin, hard, under exposed image, will, when left sufficient time in the bath in redipping, yield a fully-exposed, detailed, and vigorous negative, always exquisitely clean, uniform, and free from defect. The time which the plate should be left in the bath in redipping in order to secure these results is from forty to sixty seconds. The first plate so treated in our pre sence was of large size (14 inches by 10 inches), and was kept upwards of an hour on an excessively hot day ; but it developed satisfactorily, giving a clean, detailed, and vigorous negative. Any tendency to drying of the film is, of course, unimportant, as the whole becomes uniformly saturated again with the nitrate solution. Many photographers will not care to undertake this extra labour, except in cases where, from any cause, long keeping of the plate between exciting and developing is necessary; but it may be used, nevertheless, without much trouble, by all who suffer from matt silver and other stains in hot weather. The operation is simple : it consist s in the use of a dipping bath of distilled water, into which the plate is plunged as soon as it has acquired a creamy film in the nitrate bath. Immersion for a minute or two in the dis tilled water, with agitation of the plate, gives the film suffi cient washing, and the same bath of distilled water may be without disadvantage kept in use all day, and, if necessary, used for two or three dozen plates. Practically, it would follow that the plates immersed in the bath which had already washed a few dozen plates are in reality placed in a dilute nitrate bath, another mode of securing immunity from many of the troubles of hot weather. Some years ago we recommended the use of a second new uniodized nitrate bath as a means of getting rid of pinholes and stains. We found, in the course of the experiments made at that time,, that after exciting the plate in the usual way, immersing it in an uniodized 10-grain nitrate bath secured immunity from many difficulties, and yielded on development a perfectly good negative, without redip ping, the weak silver solution serving every purpose neces sarily in the operation of development, having, perhaps, a tendency to give more detail and less density than when a stronger solution was present. During the prevalence of the extremely ..hot weather we recommend the attention of these suggestions to any of our readers who are.troubled with stains and other defects which are brought about by high temperature. SENSITIVE ALBUMINIZED PAPER PRESERVED READY FOR USE. We were favoured a few days ago by a visit from M Romain Talbot, who introduced to our attention some samples of M. Carrier’s preserved sensitive albuminized paper, which is stated to keep indefinitely without dete rioration, and without requiring any especial care in its
