The photographic news

• Bandzählung: 12.1868
• Erscheinungsdatum: 1868
• Sprache: Englisch
• Signatur: F 135
• Vorlage: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: Hochschule für Grafik und Buchkunst Leipzig
• Digitalisat: SLUB Dresden
• Rechtehinweis: Public Domain Mark 1.0
• URN: urn:nbn:de:bsz:14-db-id1780948042-186800009
• PURL: http://digital.slub-dresden.de/id1780948042-18680000
• OAI: oai:de:slub-dresden:db:id-1780948042-18680000
• Sammlungen: LDP: Historische Bestände der Hochschule für Grafik und Buchkunst Leipzig
• Sammlungen: Fotografie
• Strukturtyp: Band

• Digitalisat: SLUB Dresden
• Strukturtyp: Ausgabe

238 THE PHOTOGRAPHIC NEWS. [May 15, 1868. appear. The fact of such a combination being established lend° support to the opinion I have hazarded respecting the chemical quality of the silver crystals employed by Mr. McLachlan. I do not, how ever, mean to assert that his black-looking article contains more than a trace of the chloride, but the presence of this body, even in a small amount, must be allowed to have great influence in altering the pro perties of so delicate a chemical preparation as the nitrate bath. A few words, finally, with respect to the amount of acid liberated in the trials by which the success of Mr. McLachlan’s expedient was in my hands established. I used 1 grain only of chloride of sodium to 700 grains of nitrate of silver, and the mixed nitric and hypo- chlorous acids, liberated at the end of seven weeks’ uninterrupted ex posure to daylight during February and March, were neutralized by 30 drops of a -grain solution of caustic potash, equivalent to 1 32nd part of a grain of solid potash, which, compared with the amount of silver nitrate originally taken, stands in the ratio of 1 : 22,400. In another experiment, performed in Mr. McLachlan’s presence, with out the chloride, the acid liberated was so small in amount that 6 drops of a 1-grain solution of caustic potash proved more than suffi cient to neutralize it; in this case the ratio stands as 1 : 56,000. These statements will illustrate some of the difficulties encountered in the chemical investigation, and would lead one to hesitate in adopting Mr. McLachlan’s assertion that nitrate of silver in pure aqueous solution suffers decomposition on exposure to light. Another point upon which he would offer an observation was the alleged precipitation of the iodide of silver. In his experi ence this had never taken place. He would not enter into detail as to his reference to ozone; but would simply remark that Mr. McLachlan was under a mistake as to the nature of that body. He had described his theory as embracing an idea that “ oxygen was absorbed by the silver from the water, actinism, and heat combined, changing it into a kind of ozone.” Now, if his (Mr. Spiller’s) notions of chemistry were right, ozone was an allatropic condition of oxygen. Silver could not take oxygen from water, because the affinities lay in an opposite direction; but if the silver could take oxygen from the water, it would form oxide of silver, and liberate hydrogen, the presence of which would be incompatible with the generation of ozone. Mr. Hooper said it would be somewhat premature to come to any conclusion on the subject at present. He thought the idea of adjusting the collodion, bath, and developer to each other was very important. As to the use of acetic acid in the nitrate of silver solution, he objected to it as generally increasing exposure. Without entering into details he thought all would be agreed that Mr. McLachlan had done a good thing in bringing his process before this Society, where the knowledge of scientific men being joined to his own practical experience, the best results might be hoped for. He did not quite agree with Mr. Fry as to the competency of photo graphers generally, as, within his knowledge, much uncertainty prevailed. He thought that photographers would gain by keep ing at least three or four baths constantly in use, so as to avoid over-working any of them. He should like to know if Mr. McLachlan had tried working his baths, seeing that boiling the developer was so useful; in his experience he found boiling as good as sunning. Mr. McLachlan had not expected that he would be believed at once. All be wanted was attention, examination, and experi ment. If he were wrong he was the only loser, as he had spent much time in the experiments, and money also, as well as in his present efforts to bring the matter before photogra phers. . As to Mr. Fry’s statement that photographers were better informed than he gave them credit for, it might be ; but he could only judge by the published information. It was quite possible, and he was disposed to believe that much more information existed amongst practical photographers than was to be found in the journals. Mr. Davis said he used excess of acetic acid in. his developer, but this was an error. It had been reported in some of the journals that he used 8} ounces of acetic acid in 16 ounces of developer, but this was a mistake, he only used 8} drachms.* As to the collodion he knew he was right in what he had said. He had made 6,000 samples of gun cotton, and had cart-loads of it by him; he had made many more thousands of samples of collodion, and therefore spoke with experience. It was an error to suppose that his was simply a neutral bath. It was a bath distinct from any other usual bath, and would dissolve a very large amount of oxide of silver. Mr. Spiller’s experiments did not meet the case; his * Mr. McLachlan undoubtedly said in the meeting 3 drachms of acetic acid, and we find it so stated in the shorthand notes ; but he subsequently, in a conversation with ourselves, in which we asked him to verify the formula, corrected the former statement, and said 3} ounces,; hence the confusion.—ED, two baths were not put out at the same time, and that which was spoiled, instead of receiving 6 drops of the potash solution, had had a much larger quantity. Mr. Spiller poured quite a gulf of the solution into it. He repeated that his was a bath difterent to any that photographers had hitherto imagined, as they would find if they would only experiment. The Chairman said it was scarcely necessary to ask them to give their hearty thanks to a gentleman who had taken the trouble Mr. McLachlan had done to bring his experiences before them. He could confirm the remarks as to the importance of maintaining, as nearly as possible, uniformity of temperature in all the preparations, as it accorded with their photographic experiences at the Royal Observatory. He thought, perhaps, it was probable that Mr. McLachlan scarcely did justice to the skill and success of practical photographers of reputation. He had been struck with the uniform excellence and freedom from defects of all kind in one plate ater another in long succession. Possibly these practical men might not have published all they knew, as it was sometimes difficult in matters gained by expe rience for a person to say exactly what he did know. How ever, they would heartily thank Mr. McLachlan. Thanks were accorded by acclamation. The Chairman, in offering Mr. McLachlan the thanks, asked him on some other occasion to let them have his experience in a tabulated form. Mr. McLachlan promised, and hoped the Society would ap point a committee to test his mode of working. The Chairman called attention to the specimen of the pre sentation picture which Mr. Robinson proposed to give to the members. Mr. DUNMORE promised to bring before the next meeting a tent, and Dr. Mann promised to exhibit some examples of the work of Professor Piazzi Smyth. The meeting then adjourned. Liverpool Amateur Photographic Association. The ordinary monthly meeting of this Association was held on Tuesday evening, the 28th ult., at the Free Public Library, William Brown Street, Mr. J. Henderson, Vice-President, in the chair. The minutes of the previous meeting having been read and confirmed, Mr. Joseph Sillitre was elected a member of the Association. Mr. Green called attention to the great number of pictures on the table, all of which had been taken this year. He re marked that he attributed the fact of so much work having been done so early in the season to the simplicity of the collodio- bromide process. The Chairman recorded his experience with various toning solutions, advocating phosphate of soda, which he had taken into use in preference to carbonate. He had used acetate of soda, but preferred phosphate. Mr. Bolton remarked that acetate of soda was the most economical, especially for amateurs. Mr. Green had used acetate of soda for some time, and cer tainly’ found it the most economical; but he had given it up in favour of carbonate, which was more convenient. The Chairman said he would like to ask the opinion of the members with regard to the action of light upon collodio-bromide plates after fixing and varnishing. He was inclined to think that exposure to light in printing had the effect of rendering the negative more dense; and he had intended making an experiment in that direction, but had not had time to do so. Mr. Phipps said he had made the experiment, some time ago, of exposing a negative to the light for about three weeks, with one-half covered with non-actinic varnish; and at the end of that time the colour was changed all over the plate from brown to purple, but no difference could be detected between the two halves. Mr. Green’s experience led him to state that the negativos do intensify after fixing, to a certain degree, and that the same effect is noticeable in wet plate negatives developed with an organic developer. It was a peculiarity which need cause no inconvenience, and might be easily met by exposing the nega tive to sunlight before varnishing, when, if rendered too dense, it might be reduced with cyanide. Mr. Lewis Hughes passed round a print from a negative taken a few days previously upon a Hill Norris plate which M I had had in his possession upwards of seven years, and which I had apparently suffered little by its long keeping.