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THE PHOTOGRAPHIC NEWS. Vol. VI. No. 223.—December 12, 1862. CRYSTALLINE DEPOSIT ON THE NEGATIVE. Most operators are familiar with a certain trouble, which usually occurs towards the close of a heavy day’s work, when a large number of negatives have been taken in one bath. The plate, on removal from the bath, appears to be covered with a gritty, sandy deposit. Sometimes it is not observed until the developer is applied. In some cases the negative does not suffer much when finished, but in others, after fix ation, it appears covered with pin-holes. This sandy-looking deposit, on examination, is found to consist of fine needle like crystals. At times the negative is working perfectly well in other respects, but at other times the appearance of these crystals is accompanied by a tendency to the produc tion of a thin fogged image. The most usual explanation of this defect has been the supersaturation of the nitrate bath with iodide of silver. When this is the case, the gradual weakening of the bath, or a fall in the temperature, would cause the iodo-nitrate of silver to crystallize out of the solution, on to the plate, on to the dipper, and on to the sides of the bath. These crystals give a rough, sandy appearance to the film, and generally end by causing pin-holes where they have been. The remedy, in this case has always been found very simple.* It was simply to dilute the bath with distilled water, to preci pitate the excess of iodide, filter out the precipitate, and add sufficient fresh silver to make the bath the proper strength. But this explanation and this remedy do not always meet the case. We have occasionally met with the defect where excess of iodide would not account for its presence. And we have recently had several cases brought under our atten tion where the circumstances were altogether different from those present in supersaturation with iodide or iodo-nitrate. In these cases this sandy or crystalline deposit would appear, in a comparatively new bath, not at all exhausted. Instead of appearing when the temperature had fallen, they appeared in the middle of a summer afternoon, when the bath had been working well during the morning; and would, probably, next morning, after the bath had rested for a few hours. These cases were puzzling ; but a history of two or three cases helped us to what we believe to be a solution of the difficulty. If we are right in our information, the latter form of this defect generally occurs with collodion which has been made some time, and which has been made with pyroxyline pro duced at a high temperature. Not having had any of the silver bath in the condition to yield the results in question, we cannot speak with absolute certainty, but from the details mentioned in different accounts which reached us, we have come to the conclusion that these crystals consist of oxalate of silver, to the characteristics of which they answer. Old collodion, or moderately new if made from pyroxyline ob tained at a high temperature, have frequently, on analysis, been found to contain oxalates, and have yielded oxalic acid in considerable quantities on being treated with the proper re-agents. It may be within the recollection of some of our readers, - that three or four years ago, Mr. J. Williams stated at a meeting of the Photographic Society, that from twenty Win- I Chester quarts of old collodion residues, he obtained oxalic acid sufficient to form upwards of twenty ounces of oxalate of lime. M. De La Haye, had also stated previously, in a I foreign journal, that various samples of collodion, when * See p. 597. | treated with potassa, yielded oxalate of potassa ; and wo believe it has since been confirmed, that one of the products I of decomposition in collodion, especially where the pyroxy- I line was obtained at a high temperature, is oxalic acid. The immersion of one or two plates coated with collodion, containing oxalic acid in infinitesimal proportions, might not produce any perceptible effect, but the result of continued I exciting of such plates for a few hours, would be a gradual ■ accumulation of the oxalate of silver, which would produce a tendency to fog, and to the deposit on the plate of needle- I like crystals, giving the sandy effect described. If the solu tion were examined at this time, it would, probably, present a turbid appearance. On standing a few hours, the infini tesimal particles of oxalate of silver, which is insoluble, would gradually precipitate ; and thus the bath be found, after a night’s rest, to work well again. As a hasty method of testing this view in the absence of the defective materials for examination, we essayed to pro duce the result intentionally. A single drop of a solution of oxalic acid was added to a bath in good condition. A general turbidity was the result, and a plate immersed at once showed a sandy deposit, like that described. On fixing a picture obtained on such a plate, the image showed a strong tendency to dissolve on the application of cyanide, the film having a somewhat green appearance where it was attacked by the cyanide, an effect we remember to have noticed before, when using old and decomposed collodion. On examining the bath shortly afterwards, a white precipi tate of oxalate of silver was found thrown down, and then the solution worked well again. If this view be correct, this defect is due to a certain con dition of the collodion, and not the nitrate bath, as has been generally supposed. It will be found to occur when using some samples, and not with others, unless they be used at once in the same bath. The source of the defect thus traced it will be easily avoided. AMMONIA DEVELOPMENT. The use of ammonia for developig dry plates is one of the few new things in photography, and may prove to be as valuable and important as it is novel. Until the conditions of its successful application are better understood, we fear that some disappointment may attend its use, as it appears capricious and uncertain. In the meantime, we may note the gradual steps by which even a decidedly new applica tion is discovered. American photographers discover—we believe Mr. H. S. Anthony was the first to do so—that submitting tannin plates to the fumes of ammonia before exposure, considerably increased the sensitiveness It was next found that the ammonia fumes need not be applied before exposure at all ; if done just before development it answered the same purpose. At this point, for some time, the matter rested. The first announcement of the use of ammonia as a developing agent is due to Mr. T. M. Leahy, of Dublin, who, in a letter dated October 23rd, published in the Puotographic News of November 7th, describes his ex periment. Having found the fuming successful in permit- tin r short exposure, it occurred to him that a solution of ammonia might answer the same end. On trying a very dilute solution prior to the application of pyrogallic acid, he found the image at once began to appear, and gradually became developed without any application of pyro what-