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94 THE PHOTOGRAPHIC NEWS. [FEBRUARY 9, 1883. In conclusion, I may state that I am quite prepared to admit that the Warnerke sensitometer is not perfect from a theoretical point of view, but feel sure few will deny that the instrument has proved itself most useful, and sufficiently reliable for ordinary use among gelatine emulsion workers.— I am, sir, yours faithfully, ARNOLD SPILLER. GELATINE EMULSION MAKING. Sir,—A professional friend of mine has pointed out that I omitted in my last letter to state why I recommended boiling to cease when the colour showed a yellowish tinge, or, as he calls it, yellow steel grey. The fact is, being an amateur landscapist, I never try for higher sensitiveness than No. 15 on Warnerke’s tablet. The colour I describe gives 15 and nothing more, or about four times the sensitiveness of wet plates. Of course, by boiling greater change is brought about, but to the detri ment of the emulsion for landscape work. The peculiarity noticed by me on development has been satisfactorily explained as the result of too much ammonia and prolonged application ; but the advantage of intro ducing bromide of zinc has been recognized, and I have made emulsion with the following:— Bromide zinc 60 grains Bromide potassium ... ... 300 ,, Iodide potassium... ... ... 4 ,, Gelatine No 1 ... ... ... 30 ,, Water distilled ... ... ... 10 ounces Acid is omitted. The bromide of zinc is dissolved in five ounces of dis tilled water, and gradually added to the gelatine in the remaining five ounces of water. The bromide potassium is added as directed, dry. Previous to melting the added gelatine, it should be soaked in water containing half-a-dram of liq. am. fort, for four hours, and subsequently be well washed by changing the water frequently. This procedure gets rid of the acid in the gelatine. Houghton’s gelatine remained distinctly acid after four hours’ soaking in running water without ammonia. If the emulsion be not coated, but added hot to the simply swelled acid gelatine, grey and green fog are likely to result. I am still anxious to know what re-actions take place, and what is the cause of the strong smell like iodine generated in the emulsion during boiling.—Yours faith fully, F. Dawson, C.B., Colonel. 2roceedings of Societies. South London Photographic Society. The ordinary monthly meeting of the above Society was held in the House of the Society of Arts, John Street, Adelphi, on Thursday evening, Feb. 1st, the President, the Rev. F. F. Statham, M.A., in the chair. The minutes of the ordinary meeting in December, and of the lantern meeting in January, having been read and confirmed, the following new members were elected:—Messrs. H. Radcliffe, C. G. Cutchey, A. Harding, Godfrey Lawford, H. Compton, Mrs. H. Compton, Messrs. G. S. Pinching, and Charles Stevens. The Chairman then called the attention of the meeting to some remarks in the annual report which had just been read anent the prize competitions, in which regret was expressed that the competition of the past year had not proved a success. He did not himself think it had not been a success; but perhaps it had not quite fulfilled their expectations, nor been such a success as similar competitions are amongst artists generally. Whether it was that the novelty had passed off, or the rewards offered were not sufficiently enticing, he could not say ; however, the committee had decided that it was desirable to continue these competitions, with some slight alteration by way of change. It had been proposed that each month the members themselves should be invited to suggest titles for subjects for competition ; these titles would be written on pieces of paper, and collected in a hat; one paper would then be drawn from the hat at random, and, if considered an appropriate subject by the majority of those present, it would be fixed upon as the subject for competition. There would be two pieces of paper given to each member, one for a landscape subject, and one for figures, which would be collected in separate hats. This arrangement was then carried out for the first monthly competition of the present season, and the subjects chosen were for landscape pictures, “ A Rural Spot;” and for figures, “The Gardener.” It was announced that pictures for competition must be sent in before the next monthly meeting, addressed to the Secretary of the South London Photographic Society, at the House of the Society of Arts. A vote of thanks was then passed to the Editor of the Photo graphic News for a Year-Book which he had kindly presented to the library of the Society. A paper was read by Mr. W. Brooks, entitled the “ South London Photographic Society’s Popular Lantern Meeting and its Lessons ” (see page 85), at the conclusion of which, The Chairman said he looked upon the contribution of this paper as a particularly kind and valuable act on Mr. Brooks’ part. Mr. Brooks, he said, modestly put forward his paper as a “ little report only of what took place at the lantern meeting, and of some of the difficulties experienced in conducting the exhibition.” The lantern meeting was a most valuable one, both to the Society itself and the public at large, and afforded a vast amount of amusement to all. Mr. Brooks had given them some very useful rules with regard to these meetings, as to what would be advis able in the preparation of slides, the order in which they should be exhibited, and also a very important point—the marking of the right face of the slide for exhibition. Mr. Brooks had referred to another most important matter, and that was, the excessive number of slides sent in, and the necessity for weeding them out. They all knew there were slides and slides, but he thought this was a matter which merited a most careful discussion indeed, for slides were received from all parts of the country, and he thought it would be the lesser evil of the two to have some slides which did not come up to the mark, rather than offend people. Mr. Brooks had also made some remarks about the character of the slides sent in ; and he (the Chairman) thought this was the most important point of all. He referred to the great advantages afforded by the oxy-hydrogen lantern in connection with the microscope, in distinguishing between the liver, tissues, &c., in health, and in disease. He was pleased to see other societies were following in the footsteps of the South London Photographic Society in establishing lantern meetings of their own, as he felt sure such exhibitions not only afforded a considerable amount of amusement, but could be made of great utility also in the interests of science, besides furnishing to photographers a fund of amusement in the preparation of slides. He was quite sure Mr. Brooks’ paper would prove both interesting and instructive. Mr. Brooks said he had had the honour of illustrating two lectures in this room, by Prof. Mosley, of Oxford, the subject being the cruise of the ChaUenger, and he would have liked some of the members to have been present to witness the combined effect of the lantern and microscope. He thought the Chairman had taken his remarks about rejecting some of the many slides sent in a wrong light. He did not wish to give the cold shoulder to any one who might make slides ; but it had occurred to him, about a fortnight before the meeting, a committee of selection might be appointed to decide what pictures were not suitable for exhibition. Mr. Brooks also referred to a matter of very frequent occurrence at these lantern meetings—viz., that some of the slides were only handed to him after the lights had been turned down, and said that in such cases it was almost a matter of impossibility for him to do them justice. He would like to hear the opinion of the meeting respecting the matter of selection of slides. Mr. Howard said that the question of lantern slides had always been one of much interest to him. He agreed with Mr. Brooks that it was an important matter, as they must remember that each slide separately had to pass the test of four or five hundred pairs of eyes. With regard to the processes used in their preparation, he thought that one hundred slides prepared by collodio-bromide would be much more likely to be successful than the same number by gelatine. With regard to the selec tion of slides, he thought that twenty-four hours before the exhibition would be ample time. Mr. Leon WARNERKE asked, with regard to some coloured