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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1300, August 3, 1883
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The photographic news
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- Titelblatt Titelblatt I
- Register Index III
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August 3, 1883. ] Street; H. H. Emmerson, Esq-, Cullercoats; G. Bruce, Esq., Duns, Berwick. Any further information will be supplied by application to Mr. Schumann, 15, Mosley Street, Newcastle-on-Tyne, or to the Honorary Secretary, Mr. J. Pike, 43, Northcote Street, Westgate Road, Newcastle-on-Tyne. DOES THE AMOUNT OF GELATINE AFFECT THE RAPIDITY AND QUALITY OF THE NEGATIVE ? BY A. L. HENDERSON.* This is a matter which deserves more attention than I think it has received. From experiments I have made lately, I have come to the conclusion that the amount of gelatine does very materially affect the quality and sensitiveness of emulsion. I know that Messrs. Sceptic, Don’t-believe, and Won’t-try, will, as a matter of course, take exception to this statement; yet ‘facts are stubborn things." I have not only reasoned the thing out, but demonstrated that my theory is correct. But I suppose I must not bring the subject forward as new, or I shall have a shower of claimants about me. One of the greatest mis fortunes I have laboured under is the difficulty I have to make myself perfectly understood. With these preliminary remarks, I will at once proceed to give my views. In the first place, I will take the case of a very sensitive emul sion, one which generally gives, when not thickly coated, a very thin imaze. In this case a small quantity of gelatine having a matt surface will give a better or denser picture, because less light will penetrate the bromide of silver. A plate giving a matt surface is always slower than when a larger quantity of gelatine is used—that is, when the same amount of silver bromide is present. I have frequently noticed (and others also) that a soft gelatine added to emulsion before coating gave quicker pictures. This I accounted for by the so-called molecular change taking place more rapidly in soft than in hard gelatine. I have somewhat modified my opinion, and to this effect: that the amount of gelatine has as much, if not more, to do with the rapidity than any molecular change. A slow plate (varying from two to ten times the rapidity of wet collodion) is usually of a yellowish or cinnamon colour when viewed by transmitted light, consequently it does not transmit as much light; and then there is scarcely a limit to the amount of gelatine that may advan tageously be added. A large quantity will allow more light to pass through, and there is a corresponding increase in rapidity. I have not yet worked out the smallest amount of bromide of silver necessary to give good results. The greatest number of plates I have coated with an emulsion made with 200 grains of silver nitrate was about thirty-six dozen quarter-plates. This emulsion, when viewed by transmitted light, was a cinna mon colour, gave splendid, dense negatives, add was about twice as rapid as my wet collodion then in use. I will not just now give you the exact formula; I will do so at another time when my experiments are somewhat more advanced. Suffice it to say that I used a large quantity of gelatine, converting half the silver into ammonia-nitrate, then boiled, getting the silver bro mide, in the first stage, in a very fine state of division. I do not say that it was a necessity to boil, but in this case I thought to increase the sensitiveness by boiling, as I did not use much ammonia. Please bear in mind that you can stop out more light with a pound of black paint than with a pound of greenish-violet, and this is about the relationship between rapid and slow emulsions. Some present may not be aware that it is not an absolute necessity to wash or precipitate emulsions, or to get rid of the salts. I have made many batches, which produced very fine negatives, by simply increasing the bulk of gelatine—say, to as much as from eight to ten times the usual quantity. I am obliged to use potassium bromide. It will be seen that when using that quantity of gelatine, and increasing the bulk of emul sion, little orno crystallisation will take place ; and I do not doubt the permanence of the uncrystallised condition of the salts in this emulsion, and therefore that the necessity for washing to remove these salts is done away with. We find gelatine lozenges and jujubes keep an indefinite time. They contain a great deal more soluble and hygroscopic salts than an emulsion such as I have described. I leave the matter in your hands for discussion. If I have not made the matter sufficiently clear, I shall be pleased to do so more fully. * Bead before the London and Provincial Photographic Association. THE ECLIPSE PARTY. Letters have been received from the English and American members of the above, giving some details which, we think, may prove of interest to our readers. Leaving England on February 17, in the s.s. the English observers made a calm passage to Colon. Here they met the American party, consisting of Prof. Holden, Dr. Hastings, Mr. Rockwell, Mr. Preston, Lieut. Brown, and Mr. Upton, to which, it will be remembered, they were to be attached. The united party then proceeded to Panama, and took ship in the Bolivia for Callao, where they arrived on March 20. Early the following morning the instruments and baggage were removed to the U.S.S. Hartford, in which the voyage from thence was to be made, and the party left Callao about five o’clock on the evening of March 22, sighting Caroline Island, the spot selected for the observations, on April 20. Although named Caroline Island, it is not a single island, but a low-lying chain of coral islets which enclose a central lagoon. The ring of islets is about seven and a-half miles in length, and one and a- half in breadth. The island, like most of its kind, is of value on account of its stores of guano, and its cocoanut produce, being leased to Messrs. Houlder Brothers, of 146, Leadenhall Street, whose agent at intervals visits this and other Pacific coral islands leased to the firm. On the arrival of the Hartford a boat, under the charge of Lieut. Qualtrough, put off to make a tour of inspection, returning with the intelligence that there were two large empty frame houses, several smaller ones, and seven inhabitants—four men, one woman, and two children— who had come thither from Tahiti two months previously. A site having been selected by Prof. Holden for the erection of the observatory, the work of disembarkation commenced. This was a matter of great difficulty, the nature of the coast preventing even the small ship’s boats approaching within several hundred yards of the shore. The boats had first to run in through a narrow opening in the reef, the boxes had then to be carried through fifty yards or so of water, varying in depth from two to three feet, next over about fifty yards of sharp irregular coral rock that cut the men’s shoes to pieces, and finally to be carried up a soft sandy beach for upwards of a quarter of a mile. However, the landing was effected without accident, and the observers took 1 oisession of their various quarters. The English observers report that the house in which they were located was a very comfortable one, containing a kitchen, dining-room, bed-room, bath-room, and store-room, and a large laboratory. Mr. Rockwell, one of the American observers, was fortunate enough to obtain the luxury of a bed. Mr. Upton another of the party, had to be content with a table, whilst the rest swung their hammocks and cots in the verandah, an arrangement which, while possessing, perhaps, advantages of its own when the weather was fine, was not altogether the best when the nights were wet. Still the observers were not un comfortable ; and if they did not “ fare sumptuously every day,’’ yet, with abundance of fish and cocoanuts, they did not live altogether badly. The weather, with the exception of one severe rain-storm, was pleasant during the sojourn of the observers, although nearly every day slight showers were brought to the island by flying clouds. On the evening of the 22nd, just as the Hartford was casting off for Tahiti, I Bclaireur came in with the French expedition, consisting of MM. Janssen, Trouvelot, Palisa, and Tacchini on board. The preparations for the eclipse proceeded briskly, and by April 28 the siderostat, equatorial, and photo-heliograph were erected and adjusted in position. The spectroscopes were next taken in hand, and the rating of the clocks proceeded with. This took some time ; but matters had so far advanced by May 1, that, from that date, with the exception of May 4, when the weather was wet, two rehearsals of the observations were made daily—one at 7, the other at 11.30 a.m. Messrs. Preston and Brown, of the U.S. Coast and Geodetic Survey, during this period made pendulum observations. By the evening of May 3 the photographers were nearly ready to take trial plates, and these they hoped to obtain the following day. The hitherto fine weather, however, changed, and before noon next day five inches of rain had fallen, and the photographic dark-room which had been erected was destroyed, all the dye being washed out of the ruby curtains and window. This damage being repaired, an attempt was made to obtain trial plates the next day, but the length of time occupied in
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