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The photographic news
- Bandzählung
- 35.1891
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- 1891
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- Bandzählung
- No. 1717, July 31, 1891
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548 THE PHOTOGRAPHIC NEWS. |July 31, 1891. The mixture, when fresh, worked very well, but very soon darkened, forming a dark brown solution, which had far less developing power than the fresh mixture. As noticed in my former paper referred to, M. Mercier states that graphol contains, among other ingredients besides eikonogen, borax, sugar of milk, and carbonate of lithia. Some experiments were therefore made with eikonogen developers containing these substances, but chiefly in the laboratory, and not by actual practice out of doors. With regard to the peculiar action of borax—in some cases as an acid, and in others as an alkali—Monsieur Mercier refers to two notes by Monsieur Aug. Lambert, on the action of borax on the polyatomic alcohols, and on the polyatomic phenols, which were published in the Comptes Rendus of the French Academy of Sciences (Vol. 108, No. 19, May, 1889). In these notes, Monsieur Lambert states the results of some experiments made in verification of Klein’s observation that mannite, glycerine, erythrite, dextrose, lvulose, and galactose, had an acid reaction with borax, while the polyglucosides, including saccharose (cane sugar), lactose (sugar of milk), and quercite did not do so, and he further shows that pyro gallic acid, pyrocatechin, the alkaline gallates and tannates, and other polyatomic phenols of the orthi series behave similarly to glycerine and the mannites, and give an acid reaction to borax by the formation of monoborate of soda and an acid boro-compound capable of decomposing carbonates. This reaction is not shown by orcin, resorcin, and hydroquinone, which belong to the meta or para series, and Monsieur Mercier has discovered that it is also not shown by eikonogen. Boric acid had already been tried by the writer as a possible preservative of eikonogen, but it was not found altogether satisfactory. Trials with borax have, however, shown that, as stated by Monsieur Mercier, it may replace the caustic alkalies and their carbonates in the eikonogen developer, and has the advantage in a hot, moist, tropical climate, at any rate, of being a definite and quite stable salt, whilst carbonate of soda, which is usually recommended for use with eikonogen, is a somewhat indefinite, and, in its crystalline form, a very unstable salt, being readily deliquescent, and apt to melt in its water of crystallisation. Carbonate of potash, though more definite and stable than the soda salt, is also very deliquescent. For ordinary work, borax seems to answer very well with eikonogen in combination with sodium sulphite ; the solution changes very little in colour, and several plates can be developed successively in the same solution, though more time is required for development in the used solu tion. The lights are clear and free from stain, and there is a good intensity of image. The following formula has been found to answer well, but should be modified as found desirable with different makes of plates or different classes of work :— Eikonogen ... ... ... ... 1 part Sodium sulphite 2 parts Borax ... ... ... ... ... 2 , Water ... ... ... ... ... 100 ,, For instantaneous work a more powerful developer would probably be necessary. Eikonogen with borax alone, without sulphite, in the same proportions as above, forms a strong developer, but the solution soon discolours and loses power. Hydroquinone also with borax alone does not answer Well as a developer ; it gives weak images and is liable to stain the film, but, with the addition of sodium sulphite, it gives pictures with good density and detail, does not stain the film, nor does the solution readily discolour. A mixture of eikonogen, hydroquinone, borax, and sodium sulphite forms a good developer, but the best pro portions have not been fixed. The addition of hydro quinone adds considerably to the density of the image, as noted already by other workers. The formula given above, with half to one part per cent, of hydroquinone, has been found to work well, but may also be modified as required. Carbonate of lithia, which is said to be one of the ingredients of graphol, though it could not be detected with the spectroscope, seems likely to be a very useful substitute for other alkalies. Its stability and definite composition as compared with other alkaline carbonates are a great advantage in an Indian climate. It certainly acts well in the eikonogen developer, giving density and detail without hardness, and in this respect, quantity for quantity, is better than borax. It is, however, only very slightly soluble in water, a saturated solution taking up only about one per cent, of the salt, or barely five grains to the ounce. It also works very well with hydroquinone, making a very excellent developer for ordinary work, and instan taneous pictures may be made with a mixture of eikonogen, hydroquinone, carbonate of lithia, and sodium sulphite in about the same proportions as given above, but sub stituting carbonate of lithia for the borax. In some cases it has been found convenient to keep the carbonate of lithia in saturated solution, and add the other salts to it. Sugar of milk (lactose) seems to be also a useful addition ; it increases density and detail in the eikonogen developer. With hydroquinone and eikonogen and borax it was found to give excessive density. As noted by Lambert, lactose does not form an acid compound with borax. I hoped to have been able to have tried experiments with various other sugars, but they did not arrive in time to be tried before I left Calcutta. It may be noted, however, that Fahlberg’s saccharin, which is not a sugar at all, seems to have some effect in increasing the stability of the ordinary eikonogen deve loper made up with sodium sulphite and carbonate, but with borax it seems to act rather as a restrainer. Pyrogallic acid will not work at all as a developer with borax, nor will hydroxylamine hydrochlorate. It may be noted, too, that the new white eikonogen in powder seems to be a great improvement on the old form of this salt. It certainly keeps its colour very much longer, though, after being open for a short time, black specks appear. It evidently contains a sulphite, but re quires the further addition of sodium sulphite to work effectively. S. S. Chusan, Aden, May 21st. Cement for Parchment Paper.—The best cement for pasting parchment paper, according to a lithographic authority, is casein glue. It is much better than so-called chrome glue, because the latter produces yellow or brownish spots where it has been employed. Casein glue is a solution of casein, which appears as whey or drop when milk is allowed to curdle. The glue is dissolved in a saturated solution of borax. When dried in the form of transparent gelatine it appears as greyish white and somewhat brittle matter, which can be easily dissolved in water, and possesses great adhesiveness. When employed for pasting parchment paper a thin paste is prepared, used in the customary manner, and the jointed places afterwards exposed | for a little while to a jet of steam.
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