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The photographic news
- Bandzählung
- 12.1868
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- 1868
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 506, May 15, 1868
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Zeitschrift
The photographic news
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Band
Band 12.1868
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- Titelblatt Titelblatt I
- Kapitel Preface III
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- Register The Index To Volume XII 619
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May 15, 1868.] THE PHOTOGRAPHIC NEWS. ■ 237 Mr. Bockett said that the tube he had mentioned had been kept in the dark. Mr. Hart said that immersion in boiling water would, in all probability, restore its pliability and elasticity. He often found that india-rubber got hard with age ; but if it were pure —and he only used the pure in his filters—immersion in boiling water, or boiling for a few minutes, restored it. After some further conversation, The Chairman stated that he had kept a sample of collo dion which he had made, which contained mixed iodides and bromides of cadmium and sodium, for upwards of three years without deterioration. Mr. England made it a practice to keep a stock in his cellar ripening, preferring to use it at least two years after mixing. Mr. Smith said he believed that Mr. Ponting’s practice was similar. A conversation on the acid bath becoming alkaline by stand ing followed; the only suggestion of a cause being the possible effect of the alkali in the powdered glass in the filter or in the glass vessel. After some further desultory conversation the proceedings terminated. London Photographic Society. The usual monthly meeting was held in the Architectural Gallery, Conduit Street, on the evening of Tuesday, May 12th, Mr. J. GLAISIIER, F.G.S., in the chair. The minutes of a previous meeting were read and confirmed, and Mr. E. Ernest Dymond was elected a member of the Society. Mr. McLachlan then proceeded to read a paper stating in fuller detail the mode of working ho described at the last meeting. He dwelt on the fact that distinctly different results were obtained by different samples of the nitrate of silver or sulphate of iron employed. Boiling'the solution of some samples of the iron salt with a little “ alkaline alcohol” was necessary to get the alcohol into “ chemical combination” with the water. He considered the use of bromides in the collodion and of nitric acid in the bath decidedly injurious. At the conclusion of his paper (which will appear in our next) he said that he was fully prepared to meet with incredulity. He would not himself have believed similar statements made by other persons. The truth of what he had said could only be tested by experiment, and he was fully prepared to go to the test with any committee which might be appointed. Mr. Sebastian Davis, after some remarks on the interest of the subject, said that he understood Mr. McLachlan to recom mend absolutely neutral collodion and bath, and very acid de veloper. The addition of an alkali on the collodion would, however, in some cases, tend to make it so powdery that the film would not hold the sensitive salts. In regard to the objection to nitric acid he agreed with Mr. McLachlan. He always neutralized any trace of nitric acid present in a new bath, and then added acetic acid. The difficulty which arose as to the developers was, that whilst Mr. McLachlan recom mended different kinds of sulphate of iron for different pur poses, he left them without information as to the differences in the samples. He proposed that some specimens be placed in the possession of the Society for analysis. He hoped that the enquiry stimulated by Mr. McLachlan’s communication would aid in eliminating uncertainties from their practice. Mr. Fry thought they now had the matter in a nutshell, and they could form a definite opinion of its value. Those who liked a spade called a spado would bo pleased with the plain speaking of Mr. McLachlan, and ho thought they ought to deal equally plainly with the subject in discussion. He should therefore make one or two remarks on Mr. McLachlan’s state ment. He had said that the vagaries of the nitrate bath were so perplexing that no experience was sufficient to conquer them. Mow was this so? Ten years ago such a statement might have appeared true, as at that time they knew much less than was now known. But were the mass of competent and capable photographers now in that position ? Ho certainly believed not. Mr. McLachlan, it appeared, thought otherwise, and he had given them a remedy which seemed to him most unlikely to aid them, but which they must wait in any case for three months before they could apply. He must confess that as a whole he could not regard the matter favorably. It seemed to him to be utterly wrong to begin with an impure nitrate of silver, and then spend three months in getting rid of the impurity. He believed there were plenty of pure samples to get. He believed that, as a rule, photographic chemicals, were as pure and as honest as any product of any kind sold in the world. The chief difficulties which at any time arose were simply due to want of experience. But the want of experience in individuals must not be taken as an illustration of the con dition of photography among competent men. For instance, they had at a recent meeting an interesting statement of the difficulties of an amateur in South Africa, from which they might have been led to believe that Natal was as full of troubles to the photographers as to the ecclesiastical world ; but the simple truth was, these difficulties arose from want of ex perience. In fact, he must say that he agreed with a recent writer* who said that the error of Mr. McLachlan was that he under-rated the capabilities of photographers. But if some people would make very small baths, and use them much, or would doctor their baths, they ought not to be surprised if at times they were beset with troubles and uncertainties. Mr. Spiller said the especial aim of Mr. McLachlan appeared to be to introduce harmonious conditions into the pre parations with which he worked. For this aim he gave him all credit; but when he entered into the detail of his propositions he felt somewhat at a loss. When Mr. Foster and himself received the communication upon which they had already re ported, they found a difficulty in the fact that Mr. McLachlan frequently used terms in which he gave a new sense to old definitions. For instance, he had talked to-night about alka line alcohol, whilst chemists knew that alcohol could neither be acid nor alkaline. Then they were, at the outset, at a loss to identify the various salts described, and to the present time, he had no idea of what the peculiarity of the nitrate of silver recommended consisted in. Could Mr. McLachlan now show him a sample ? Mr. McLachlan handed an unlabelled bottle containing white crystals to Mr. Spiller, who pronounced the contents to be iodide of potassium. The mistake being rectified, and a sample of the nitrate of silver produced and examined, Mr. Spiller proceeded : Of course he could not venture to speculate on the nature of the impurity present in the salt at present, but he had been led to believe that it was not impro bable that it contained chloride of silver in combinations, and a sample which he now produced contained one per cent, of chlo ride in combination with the nitrate. In his remaining obser vations he would read some brief notes of the experiments he had already made :— Ten days after Mr. McLachlan described his new system of pro ducing negatives in the statement made at the last public meeting of this Society, I published in the Photographic News (April 24th) a letter or article entitled “ Observations on Mr. McLachlan’s Pro cess,” in which I suggested the possibility of chlorine taking part in the decomposition said to occur when the nitrate of silver in the form of conedaqueous solution is exposed to sunlight. My grounds for believing in the possible occurrence of chlorine were, firstly, the description given of a special quality of nitrate of silver which is sometimes to be met with in the form of “moist and dirty-looking crystals,” such as would ordinarily bo rejected by pho- tographers, but now is to be preferred. Secondly, that chlorides are amongst the most commonly occurring impurities in water, and are almost invariably contained in commercial qualities of nitric acid; so that in the preparation of nitrate of silver from an inferior acid and the use of anything but the purest description of distilled water, there would be some probability of chloride of silver being intermixed with the nitrate, and forming a combination which is affected bv exposure to light. I have since made direct experiments on this point, and find that chloride of silver is much more soluble in the nitrate than my pre vious experience led me to anticipate. I exhibit a sample of crystal lized nitrate containing one per cent, of chloride of silver in intimate union, if not, indeed, in.direct chemical combination. Such a pro duct must always be in the form of small crystals, and, unless special precautions are adopted, would invariably be discoloured by light.. I made it by dissolving 1-17 grains of rock salt (pure chlor, of sodium) in a small quantity of water, and adding 340 grains of pure crystallized nitrate of silver. The precipitate at first formed soon became redissolved upon warming and consequent evaporation of the water, the chloride of silver being, to a certain extent, soluble in a strong solution of the nitrate, and apparently having the power of crystallizing with it. A special experiment to decide the extreme limit of solubility of the chloride and a warm saturated solution of the nitrate showed that it was possible to dissolve as much as 47 parts of chloride in 100 of the nitrate. A compound containing this high proportion of chloride cannot, however, be manipulated, for on adding a mere trace of water the white curdy precipitate begins to * See Echoes of the Month in our issue for May 1st,
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