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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1296, July 6, 1883
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The photographic news
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Band
Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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Band
Band 27.1883
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July 6, 1883. J naturally conclude that the most easily reduced body—viz., the indigo-sensitive bromide—would prove in actual prac tice to be the most sensitive. This, however, is not the case, as the sensitiveness depends rather on the relative power of the two isomeric bodies to absorb light. In the case of the blue-sensitive modification, this absorptive power is much greater than in the case of the indigo sensitive modification. ON HYDROKINONE AS A DEVELOPER. BY EDWIN BANKS.* In response to a request from the Hon. Secretary that I should read a paper before you this evening, I thought that the subject of development and developers, with a short account of the newest addition to the list—namely, hydrokinone—would per haps be of some interest. The theory of processes and formulae for obtaining sensitiveness and vigour in sensitive plates has been discussed over and over again for years past, and still remains as open to discussion as ever. Every process in photo graphy is capable of many variations, each one of which will produce good or bad results according to the skill or practice of the operator, and what one person succeeds with, another is apt to condemn as useless. The subject of development, however, has not proved capa ble of so many variations as other parts of the routine in pro ducing a picture. The number of developers in use is also very limited. Until about six years ago we only had two that were available in negative work—namely, ferrous sulphate and pyrogallic acid. The iron developer, made acid with acetic acid, was employed in wet plate, and pyrogallic acid principally for the various dry processes. Sulphate of iron development underwent very little change during its whole history. The formula recom mended thirty years ago, although repeatedly modified by the addition of various organic substances, still stands as the best in the wet process at the present day. Pyrogallic acid, however, has had many changes. Originally employed as the developer for negatives with a bath, it gave way to the more energetic sulphate of iron, took second rank, and was used as an intensi fier or re-developer. In all dry processes it always held its place, its organic constitution rendering it better capable of developing a dried film than iron proved to be. Most of you will remember the impetus given to dry-plate photography by the discovery that an alkaline solution of pyro would develop a dry plate far more energetically than would an acid solution with silver. It was from this period that dry processes began to advance into the rank of practical utility, until, by the accumu lated researches of so many minds, they have advanced to their present prominent position. If it had not been for this varia tion in the method of development, all our modern processes would have been unknown ; and, in all probability, further advances in the science will be brought about by researches in the same direction. There is in development and developers an almost unlimited field for investigation. About six years ago Mr. M. Carey Lea published a series of papers on new modes of development, and announced the dis covery of the developing power of ferrous oxalate when held in solution by oxalate of potash upon films containing no free silver —that is to say, development took place at the expense of the film itself, and not by precipitation upon its surface. Most of you have employed this developer, and are familiar enough with its valuable properties ; and for many purposes it still holds first rank. In the same paper Mr. Lea gives the result of a great many experiments with a large variety of organic substances, which, from their chemical constitution, might be regarded as possible developers. It is a communication full of interest, and suggests many directions for research, and it is unfortunate that more attention is not given to improvements in using and varia tion in the substances employed for development. That the possible developers are extremely numerous will be seen at once by referring to the experiments of Mr. Lea, to which 1 have re ferred. All the experiments were tried upon paper prepared with iodide, bromide, and chloride of silver, washed free from all trace of nitrate. For the benefit of those present who cannot conveniently refer to the article, I will mention briefly a few of them which were successful in giving a vigorous development, and which seemed worthy of further experiment. Ferrous oxalate is well known, • Read before the Liverpool Amateur Photographic Association. and also Captain Abney’s modification of it, when dissolved in citrate instead of oxalate of potash ; but almost any organic acid saturated with a ferrous oxide will develop an image, especially the lactate, salicylate, and succinate. Amongst the glucosides, sugars, and resins, many were found capable of giving very promising development, especially guiacum, which, dis solved with an alkali, gave development no far inferior to pyro gallic. Everyone knows that a developer which is eminently suited for one process, is not adapted to another. Pyro and ammonia succeed well with gelatino-bromide dry plates, but is unsuited for gelatino-bromide paper. - Where one developer begins to fail, another steps in and supplies the deficiency; hence my reason for drawing attention to the wide field open for research for those who have time, inclination, and—most important of all—patience. In the numerous applications to which photography is applied, every variety of developer would readily find its appropriate sphere of usefulness. The latest, and what bids fair to be, peihaps, the most useful addition to our developers, is the more immediate subject of this paper. Hydroquinone, or hydrokinone, or quinol—for it is known by all these names—partakes very much of the nature, of, and is closely allied to, pyrogallol. Like pyrogallol, it is a deriva tive of benzine. The solution of it is neutral to litmus paper. It has a powerful attraction for oxygen, absorbing it, when dis solved in water from the atmosphere, and more rapidly when rendered alkaline, though in neither case does it do so as rapidly as pyro ; hence its solution will keep better, and, when mixed with alkali, retain its developing power a longer time than pyro. The chemical formula is also very similar. Pyrogallol has C,Ha(0H)a, and quinol CeH(0H)2 ; so that, it will be observed, whilst each contains six atoms of carbon and six atoms of hydrogen, which is the composition of benzine, pyrogallic contains three atoms of oxygen, and quinol only two. Another resemblance to pyro consists in the fact that both exist in nature in certain vegetable productions ; pyro, exists as gallic acid in gall-nuts and oak bark, and quinol as arbutive in the leaves of the arbutus, or bearberry, and other Jlricacia. Commercially, quinol is made from aniline and from carbolic acid, both also benzine derivatives. It is first obtained as quinone (C,H,0,) by the oxidation of aniline. One part of aniline is dissolved in eight parts of sulphuric acid diluted with twice its bulk of water. After cooling, a saturated solution of two and a-half parts of bichromate of potassium is added very gradually to avoid too great rise in temperature. At first a thick, pulpy mass of aniline black is formed, the reaction being the same as that which takes place in the aniline printing process. This shortly changes to a dirty-brown solution. It is then treated with sulphurous acid in excess, when quinol or hydro kinone is formed. This is extracted from a solution by ether, and on evaporation crude quinol is left. Other methods are given, but sufficient has been said to give an idea of its nature. Its characteristics as a developer is what possesses the most interest to photographers. Captain Abney, who, I believe, was the first in this country to draw attention to its developing power, says that it is twice as powerful as pyro. It is very certain that it will bring out a fully-developed picture with at least half the exposure neces sary when pyro is employed. At first sight this appears strange when it is observed how much more powerfully pyro absorbs oxygen ; but the explanation probably is in the fact that hydros kinone is more gradual in its action, and has a more “ selective ’’ power than pyro. With a collodio-bromide film, for instance, which is not so much protected from chemical action as a gela tine one, pyrogallic acts with such energy, when mixed with an alkali, that the whole film is reduced immediately, and no image, or only a faint one enveloped in fog, appears ; hence there must be used a powerful restrainer to keep this action within bounds. A soluble bromide which is usually. used has this effect, but, unfortunately, at the same time, partially undoes the work which the light has done, rendering it necessary to give longer exposure. But with hydrokinone no restrainer is neces sary unless a great error in exposure has been made. It does its work rapidly and clean, in this resembling the ferrous oxalate ; it does not discolour during development so much as pyro, and consequently does not stain the film so much, whilst full printing vigour is very easily obtained without having to resort to intensification. The colour and general appearance of the negative also is more like the wet-plate process, since the shadows remain so clear and free from fog. It seems almost impossible to fog a plate with it.
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