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The photographic news
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- 35.1891
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- 1891
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- Bandzählung
- No. 1693, February 13, 1891
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The photographic news
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February 13, 1891.] THE PHOTOGRAPHIC NEWS. 123 NOTES FROM INDIA. BY COLONEL J. WATERHOUSE, B.S.C., ASSISTANT SURVEYOR GENERAL OE INDIA. Preservation of ErKONOGEN. Professor W. K. Burton’s paper on this subject, in the latest number of the Journal of the Photographic Society of India, is very interesting and valuable, especially as he seems to have found a satisfactory solution of a problem on which I have been working, more or less intermittently, for some time past. I have not yet tried the method he recommends for washing the eikonogen crystals, and then keeping them in a twelve per cent, solution of sodium sul phite, but, from my experience in the same direction, I have no doubt that it will answer well; the sulphite, how ever, must be good, and not alkaline. From recent notices in the European journals, it appears that the Ger man manufacturers of eikonogen have succeeded in making a product that does not darken or decompose with heat and moisture, and it is said that this is brought about by the addition of a bisulphite. The new product is a white powder, and is most probably thoroughly desiccated, so as to drive off the water of crystallisation, to which may, in great part, be attributed the darkening of the eikonogen crystals. In dry air at a low temperature they keep well, but in moist air at a high temperature, as is the case here and in most tropical countries, they rapidly get into a moist, pasty state, darken, and decompose. Some eikonogen of English manufacture lately received is in salmon or pink granite coloured crystals, and, so far, it shows no sign of discolouring, but whether it will stand the quickly approaching hot weather remains to be seen. Although Professor Burton has succeeded with the treatment with alcohol I suggested in a former number of the News, I find that it does not answer so well as I ex pected it would. Some crystals that had been cleaned with an acid solution of sodium sulphite, much in the same way as recommended by Professor Burton, remained white for a very long time in spirit of wine; but some fresh crystals put into absolute alcohol did not keep nearly so well, and the alcohol has extracted a good deal of a yello w substance. As Professor Burton remarks, in order to make the treatment by alcohol efficient, the spirit must be changed two or three times, as it draws out and be comes weakened by the water of crystallisation from the crystals. Precipitation of the eikonogen by acids has also been recommended as a means of keeping it in good order. I have tried several acids in a cursory way with out quite satisfactory results. Phosphoric acid seemed to have a powerful action in keeping the solution free from darkening. Eikonogen is such a valuable developer, and so pleasant to work with, that so satisfactory and simple a means of keeping it in good order in tropical climates as that recommended by Professor Burton is very wel come. It may be noted, with reference to the use of the dark coloured washings of the eikonogen crystals as an ink, that, although it does make an admirable writing fluid, it is so easily washed off the paper that it is quite unsuitable to serve as an ink to be used for any permanent record. Thio-Carbamide Reversals. Since the warm weather in September and October, I have not been able to make much progress in working out the direct positive process till lately. However, on taking it up in cooler weather, it was found that better results were more easily obtained, and some new experiments seem to have brought me almost within reach of a practical method, though much has yet to be done in working it out and perfecting it, so as to obtain perfect positive pictures with certainty. The principal difficulty all through has been to secure clear lights with good detail in the shadows. If the high lights are clear, the shadows are too deep; and if the shadows are clear and well detailed, the high-lights are liable to be over-done and unreversed. This is particu larly the case in outdoor work with sky and trees, or dark foregrounds. It was evident that something was wanted which would more completely reconvert the reduced silver in the more exposed parts into silver haloid salt, so that it might be dissolved out by the fixing agent. This, I found, could partly be secured by prolonging the development, and allowing the reversing agent plenty of time to act and complete the reversal. The image thus produced may be too dense for printing purposes, but can be reduced, after fixing, with bromide or chloride of copper, so as to gradually bring down the lights and details till they are sufficiently clear, though the operation has to be conducted with some care to avoid uneven reduction. A preliminary treatment of the plate with dilute hydrobromic acid was tried, but was not found better than the dilute nitric acid, previously used with advantage. In a leading article on the process which appeared in the British Journal of Photography for October 24th, attention was drawn to a curious compound of thio carbamide and ammonium bromide, which was first described by Prof. J. Emerson Reynolds in a paper published in the Journal of the Chemical Society of London for 1888, and to which he gave the name tetrathiocarbamid- ammoniumbromide. This salt is quite easily prepared from thio-carbamide, and a trial of it has given me some very good results, better in many respects than those obtained with other thio-carbamides, and it acted in every way much better than the plain thio-carbamide. Prof. Reynolds’ instructions for preparing the new salt are to dissolve 1 part of ammonium bromide in as small a quantity of alcohol as possible, and add it to a nearly- saturated boiling solution in alcohol of 3-04 parts of pure thio-carbamide. The boiling is continued for some time afterwards, and then the flask is allowed to cool. On standing, the contents will be found to set into a mass at the bottom, and may be re-dissolved in alcohol for use. I find that about five drops of the strong alcoholic solution of this salt to the ounce of developer are sufficient, but in some cases more may be added during the development. It is important that the alcohol should be strong, because water decomposes the salt. In making up some of the salt, a little water found its way into the flask, and the product so obtained seems to work quite differently to the proper compound salt. It is remarkable with what very short exposures strong, vigorous positives can be obtained by the addition of only a few drops of the solution of this salt to the eikonogen developer. In a case where the ordinary exposure with pyro development would have been from sixty to ninety seconds, ten seconds was found to be more than sufficient, and the exposure was actually reduced to two seconds. This enormous shortening of exposure points to what may eventually be one of the most valuable applications of this curious process, and that is to astronomical photography. Already, by the use of gelatine dry plates, the photo graphing of stars, nebula?, and other heavenly bodies has been greatly facilitated, and made to render thoroughly
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