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May 16,186*2.] THE PHOTOGRAPHIC NEWS. 237 tccti” >i< el. dM a t bala coe f bde ‘CP 1 b 11 V qop” ,e" ge"e W j”’ 0 i‘” n> yiP• 0 tiob" .o Notes they would hold him as legitimately excused. They would allow him now, he hoped to exhibit the results he had brought with him, and make some comments thereon, for the subject would necessarily produce an animated discussion, and he would then, with their permission, take up the subject after the recess, when he hoped to bring before them a more complete paper than he could possibly have done had he written one for the present meeting. There had always been a great deal of conflicting evidence as to the increased sensibility im parted to collodion by the introduction of bromides, and many men, standing high in the profession, had recorded their opinion that there was nothing gained by their introduction. One thing was, however, certain, that bromides had produced such a uniformity of action in collodion, that, even if they were to admit that, under the most favourable circumstances, a simply iodized collodion could be made to give results as rapid as one containing a bromide, still all must admit that their introduction had tended in no small degree to improve the pro ductions of photography, for, whereas, an iodized collodion giving good results a few days after iodizing, would, at the end of a few weeks, bo comparatively useless for rapid purposes, the introduction of a bromide would render it as useful at the end of as many months. He would now pass round the results of his experiments as far as he had gone, and he thought the value of bromides would be found very evident. His first experiment was with two samples of collodion on one plate. Both were prepared about six months ago. One half of a plate was coated with collodion iodized with iodides of cadmium and ammonium, 84 grains to the ounce. The other half with iodide of ammonium 4} grains, bromide of cadmium 1 grain. It would be seen that the bromo-iodized half was clean and full of detail, whilst the simply iodized half was dirty and under-exposed. This experiment was made in a bath quite new, and nearly neutral, giving, with the collodion ho usually employed, instantaneous results. There was no Colour to indicate the liberation of free iodine in the simply ioxlized sample. Experiment II.—One half of a plate was coated with a collo- dion bromo-iodized as follows:—Iodides of cadmium and ammo- ninm 4+ grains, bromide of cadmium 2 grains. The other half with collodion iodized with iodide of potassium 3 J grains newly iodized. The bromo-iodized half was perfectly clear and brilliant, whilst on the iodized half there was the ghost of an image covered by fog. The experiment did not quite satisfy him, for the iodized collodion was altogether only 24 hours old, and, therefore, could not bo in its best condition. In Experiment III, he took the same iodized collodion as in tle last for one half of the plate, and introduced 1} grains of bromide of cadmium into a portion of the same collodion for he other half of the plate. This was sensitized in an old bath, hoth halves indicated under-exposure, but the bromo-iodized "I was much the best. Experiment IV was a repetition of the last, but instead of ling the instantaneous shutter employed for all the other, Periments he gave about 2 seconds. The bromo-iodized half Bquite clear with the exposure about right, whilst the iodized p was partly fogged, but indicated under-exposure. nzperiment V was with iodide of ammonium 2} grains, bro- 0do of cadmium, 5 grains, for one half of the plate: bromide vsadmium, 5 grains, for the other half. It would be seen that Eurere bromide was employed alone, there was but a faint pic- ,, 1 ■’ and that the introduction of 2} grains of iodide had nderfully improved the results. ] a * appeared, however, that where the bromide was present in f, Quantities, a corresponding amount of iodide was necessary a to 8 best results, for it seemed that the excess of bromide had pointeney to rob the iodide of a portion of its creaminess. The Cromi he wished to determine in his experiments was, how much moro 4 8 to use with the greatest advantage ; he hoped to have the re ° say on this point when he resumed the subject after devele Ce88. Al! the preceding results were produced by iron acotil pment ’ iron, 80 grains, with a very small quantity of H's not more than 10 minims to the ounce. iodide next experiment was made with collodion iodized with of potassiPotassium, 32 grains, for one half of the plate ; iodide the other 1ae22grains; bromide of cadmium, 1} grains, for acetic acid in ’ but developed with pyrogallic acid, 2 grains ; half gave a 4 minims, to 1 ounce of water. The bromo-iodized iodized half sn picture with plenty of half tone, whilst the ted colour wi a complete reduction of silver all over of ruby ’ c 1 would indicate an alkaline condition of bath or over-exposure. Unfortunately, he had not this result with him, for oh washing it after fixing, the whole film washed off. He was unprepared for this, for in all the other results with iron development he had taken no care whatever in the washing. It appeared, however, that the pyro exercised some influence upon the film, which made it unable to bear rough treatment. He thanked them for their patient atten tion to his imperfect remarks, and he hoped to go more com pletely into the question next season. Mr. HARMEE remarked that he had often observed a much greater tendency in the film to leave the glass when developed with pyro, than when developed with iron, and especially that it would not bear treatment with bi-chloride of mercury after development with pyro. Mr. Wall had met with similar experience. The Chairman said the use of bromides was a subject which had long engaged his attention, and some time before it had re ceived much consideration from the photographic world he had come to some definite conclusions on the subject. It was necessary to preserve the different aspects of the subject quite distinct, and consider each part of it under its own most favour able conditions. In speaking then of the respective advantages of simply iodized, or of bromo-iodized collodion, it was neces sary to have reference to the developer ; and the question which arose was whether simply iodized collodion with pyrogallic acid development, or bromo-iodized collodion with iron development presented the greatest advantages. He thought experiment generally, and his own experience certainly, was in favour of the latter. Another point which had not, he thought, received sufficient attention, was the different effects produced by different bromides. His own conviction was, that a bromide with an alka line base was much more efficient than the bromide of cadmium ; a small proportion of the bromide of potassium, for instance, much more readily reduced over-intensity, and gave softness and half tone than a larger proportion of bromide of cadmium. The character of the pyroxyline was another important element in the consideration. Where a bromide was used he preferred a pyroxyline which tended to give an intense image when the collodion was simply iodized; the addition then of a small por tion of bromide gave the maximum of advantages, in rapidity, cleanness, and delicacy, and in reducing the density which would be present when an iodide alone was used. The bromide of cadmium he had not found so efficient in this respect, and larger quantity was necessary. Another element to be con sidered was the character of the lens to be employed. The use of a lens of long focus reduced the intensity of the light, and had a tendency in like ratio to reduce the intensity of the re sulting picture ; whilst if a compound lens of short focus were used, the image was very brilliant and intense. It was clear that some modification in the collodion was necessary in these two cases, and the collodion which gave a sufficiently dense picture with a lens of long focus, would probably give a picture too intense with a lens of short focus, and this over-intensity might be reduced by the addition of a bromide. It must not be for gotten, however, that some samples of pyroxyline were of a character unsuited to the use of bromides, and that in such cases the best results were obtained by their omission. Ho mentioned these points to remind members that the question was one which required considering in all its aspects. The uso of a bromide, for instance, was not always an advantage if pyro gallic acid development were used. When they camo to iron development, however, the advantages of a bromide were be yond a question, both in sensitiveness and cleanness. The point at issue, however, seemed to be whether greater sensitive ness was obtained with a simply iodized collodion and pyro gallic acid development, or with a bromo-iodized collodion and iron development. He had no doubt himself that with a bromo- iodized collodion and iron development, more sensibility could be obtained than with the most rapid simple iodide and pyro. Still there were interesting points to settle, and as ho under stood Mr. Blanchard, he was not satisfied that as yet he had given the iodides alone a fair test. Mr. Blanchard : precisely. The Chairman, continued, the iodized collodion which gave fog was probably too newly iodized. It should have been iodized at least 24 hours to secure its best conditions. Mr. Blanchard said his newest sample had been iodized that length of time; but he thought probably a longer time might be better. The Chairman said that each should bo tried under its own best conditions of bath as well as developer.
