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The photographic news
- Bandzählung
- 6.1862
- Erscheinungsdatum
- 1862
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- Hochschule für Grafik und Buchkunst Leipzig
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 217, October 31, 1862
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Zeitschrift
The photographic news
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Band 6.1862
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- Register Index 619
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Band 6.1862
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526 THE PHOTOGRAPHIC NEWS. [October 31,1862. ing, the iodide of cadmium is deposited pure in a crystal line state. The alcohol is decanted and heated, and will serve for new preparations upon the addition of a little fresh alcohol. In a word, persons familiar with chemistry, will see that the operation is continuous, and that it may be practised, economically, on a large scale. From 166 parts of iodide of potassium employed we obtain: Cd = 56 I = 127 • 183 parts of iodide of cadmium. We recommend those persons who make this preparation for their own use, to make use of the liquid dried in the stove, but not treated with alcohol. The quantity of sul phate of potassa which is thus mixed with the iodide of cadmium is so small, that it may be neglected in formulas; and. moreover, the sulphate of potassa is completely insoluble in the liquid of which collodion consists. The purest cadmium is that of the Vielle Montagne (Belgium). That from Silesia frequently contains copper. The price, in quantities, is 3s. to 4s. per pound; by retail that price is doubled. The price of iodide of potas sium varies from 8s. to 9s. per pound. The price of cad mium is about 8s. or 9s. per pound. These prices are much higher when sublimed iodide is employed. When iodide of cadmium is prepared with precipitated iodine, it is always yellow, and contains many impurities. Bromide of cadmium may be prepared in the same man ner; but the old method is preferable, because bromine separates much more readily. We must, however, not omit to observe that bromine as now prepared, almost always, contains much chloride, in the shape of chloride of bromine, a substance which so much resembles bromine, that a chemical analysis is required to detect it. In such case the bromide of cadmium necessarily contains muck chloride; but this chloride, somewhat less soluble in alcohol and ether than the bromide, separates at the expiration of a few days.—Le Moniteur de la Photographic. 9roceedings of Sotieties. North Loxdox Photogbaphic Association. The usual monthly meeting of this Association was held on the evening of Wednesday, the 22nd, inst. at Myddelton Hall, Islington, Mr. G. Shadbolt in the chair. After the usual routine proceedings, the following gentlemen were elected members of the society: Messrs Paigetor, Fisk, Layte, and Whiting. Mr. G. Dawson then read a paper on the causes of fading in photographs. The chief cause he held to bo the action of sulphur, and recommended the very careful washing of prints, and final immersion in salt and water, before toning and fix ing, so as to eliminate every trace of free nitrate, because either that salt, or carbonate, or acetate of silver, would decompose the hyposulphite and set up sulphur action. He also endorsed the announcement which recently appeared in our pages, to the effect that silver was to be found in the whites of all albumen- ized prints, no matter how they had been treated, but expressed a conviction that the compound existing was insensitive to light, and that as yet it was not proved to exercise any detri mental influence on the permanency of the picture. A conversational discussion followed in reference to the printa which had faded in the International Exhibition; the haste with which many of them had necessarily been prepared being alleged as one of the causes of fading, while such a cause was entirely disallowed by other members. Mr. Hill said he had been troubled lately with a brown stain frequently occurring at the back of his prints for which he could not assign a cause. Various suggestions were offered as to the probable cause, such as the use of dirty clips, the action of bits of bibulous paper when placed to assist in drying the excited sheet, touching with fingers which had come in contact with hypo. Mr. Hill did not think that any of the suggestions met his case. Mr. Seeley asked if maintaining the hypo fixing bath in a decidedly alkaline condition, would not prevent the generation of acid from free nitrate, &c. Mr. Dawson said that if nitrate, acetate, or carbonate of silver were introduced into the hypo bath, no matter whether it were alkaline or not, decomposition would ensue, and sulphur be libe rated. He recommended that all free silver should be at once converted into chloride before toning. It was not important how much salt were used, if care were taken to have plenty. After some further conversation on the subject, in which the Chairman, Mr, Dawson, Mr. Simpson, Mr. Hill, and Mr. Seeley took part, The Chairman referred to the allusion made by Mr. Dawson to Mr. Spiller’s recent statement in our columns, to the effect that the whites of fixed albumenized prints contained silver, and stated that he (the Chairman) had since corroborated, by experiment, the statement. Mr. G. Wharton Simpson said, in reference to Mr. Dawson’s statement, that the compound of silver and albumen thus left in fixed prints, was not acted upon by light, that he thought the non-sensitiveness was not satisfactorily ascertained. He had recently had an opportunity of examining a number of vignetted albumenized prints, which presented a large surface of white. That part of the whites which had been submitted to the action of strong light, was slightly discoloured, having something of a yellow or creamy tint, without, however, any signs of fading. The portions of the same prints which had been protected by a mount or passo-partout, remained per fectly white. He thought it was probable that this change of colour was, probably, duo to the action of light on the trace of a silver compound left in the print. Mr. Dawson said it was possible that the continued action of a strong light might affect the compound. He had only tried it in a test tube, and with a short exposure. The Chairman referred to the fact that in some thick plain papers, especially when sized with animal size, he had, on applying the hydrosulphate of ammonia test, found traces of silver. After some further conversation on the subject, Mr. H. Cooper, jun., read-a communication on “ Resinized Paper (see p. 524). At the conclusion of the paper he ex hibited a number of very fine prints, the results of different experiments. Some of these were fine specimens of the effect to bo obtained by double printing, and Mr. Cooper gave some explanations of his method of proceeding to produce the various effects. (A paper on the subject, by Mr. Cooper, will appear in our next.) Mr. Dawson asked if the use of resin gave abetter tone than Iceland moss, or Irish moss. Some of the finest tones ho had ever seen wore produced by these additions to the salting bath. Mr. Cooper said the resin gave a better Ione, and one which he preferred, and it gave more vigour. The prints now exhi bited were, many of them, experimental prints, and by no means examples of the best possible results. The Chairman thought there was not sufficient brilliancy to render it likely that albumenized paper would be superseded. Mr. Cooper thought that for largo prints it might be. Mr. Hill thought for some subjects the effect was better. A discussion then followed on the tendency of resins to become yellow. The Chairman believed that all rosins had this tendency. Mr. Cooper said the specimen of frankincense he had used was perfectly white, and it had been five years in the hands of the retailer. How much longer it had boon in wholesale hands he could not say. Mr. Martin believed that all resins on exposure oxidized and turned yellow. In answer to a question Mr. Ross stated that Canada balsam, exposed in a bottle to the sun bleached and became whiter. Mr. Martin said that, in that case, it was protected from oxidation. Mr. Dawson said he was afraid that oxidation was a conve nient term often applied to effects of the real nature of which we knew nothing. After some further conversation on the subject, Mr. Seeley said that he had recently been informed that in the photographic department of the South Kensington Museum
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