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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. 1276, February 16, 1883
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- Titelblatt Titelblatt I
- Register Index III
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108 THE PHOTOGRAPHIC NEWS. [Febbuaby 16, 1883. changes of water until the whole of the hypo has been removed. To ascertain if this is the case, sufficient tincture of iodine should be added to some water to give it a light sherry wine colour, and to this a little starch paste (made by dissolving a few grains of powdered starch in some hot water) ; the two will combine together, and form a blue com- pound-iodide of starch. Taking a plate and holding it over a white ground, pour on a little of the blue compound, when, after rocking for a short time, if the blue colour remains, the plate, and similar ones washed in the same manner, may be taken as thoroughly free from hypo; but if the blue colour is destroyed, there is still hypo in the film, and the washing must be continued. After washing, the plate should be allowed to dry, and a proof printed from it to ascertain if the density and character of the image be satisfactory. Supposing this to be the case, the plate is made hot over a ring gas-burner or other suitable source of heat, and coated with varnish, the heat being maintained until the varnish is dry, to ensure a transparent film. There are many formul employed for varnishes; the solution of pure shellac in alcohol supplied by Hopkin and Williams, if diluted with an equal bulk of alcohol, answers very well. FREEING EMULSION FROM SOLUBLE COLLOIDS. BY A. HADDON.* Ar a recent meeting, when we had the pleasure of hearing Mr. W. K. Burton’s communication on his improved method of preparing gelatino-bromide emulsion by the precipitation method, I said from the chair, in answer to some remarks made by Mr. A. L. Henderson, that the difference he had observed between the precipitation method and the ordinary washing method, when the two emulsions were prepared in exactly the same way, might perhaps be due to the fact that in the case of washing the emulsion in shreds none of the decomposed gelatine was able to get out, whilst in the precipitation method the whole, or nearly the whole, was got rid of by decantation. Mr. Henderson has since then, I think, been making some experiments with “ leucine,” and has come to the conclusion that I was wrong in my statement that “ leucine ” will not pass through a gelatine or vegetable parchment septum. With a view, therefore, of settling this matter once for all, I began some experiments on Monday last, and the results of my experiments fully bear out what I said on the occasion referred to. Last week Mr. Henderson presented me with a bottle of “ leucine,"t and I have carried on my experiments with his own material, so that there can be no doubt as to the kind of " leucine,” metagelatine, or soluble gelatine that I have used. In order to make my experiments resemble as closely as pos sible what happens in an ordinary set emulsion, I took a short piece of glass tubing about an inch in diameter, ground one end flat, and covered it with a piece of blotting-paper which had been soaked in a tolerably strong solution of Nelson’s No. 1 photo graphic gelatine, the paper being cemented to the glass by means of gelatine. Five cubic centimetres of “ leucine ” were placed inside this small glass vessel, the whole supported in seventy-five c.c. of distilled water, and left in this state for forty-five hours. At the end of that time the contents of the tube, and the water in which the tube was suspended, were evaporated to dryness over a water bath. The residue from the evaporation of the contents of the tube weighed -0925 grammes. The residue from the distilled water weighed '0378. Adding these two together we get the solid residue, at 1008 C., as '1303 grammes. On evaporating five c.c. of the “ leucine ” without any previous treatment, the residue weighed ‘1217 grammes. The increase in weight where dialysing has been going on can, I think, be accounted for by taking into account the prolonged action of the ammonia contained in the " leucine " on the soft gelatine of which the septum was made. I hoped to have been able to lay before you the results of Borne other experiments I have been making with vegetable parchment; but just at the last moment I spilt the contents of the glass tube after it had been dialysing for forty-two hours. From the result I have obtained I think you will agree with • A communication to the London and Provincial Photographic Association. t By “leucine” Mr. Henderson means gelatine whose setting power has been destroyed by boiling with ammonia. me that simply washing set emulsion in water is not the proper way to remove the decomposed gelatine; in fact, I doubt whether more than two or three per cent, of the decomposed gelatine can be removed in that way. You may naturally ask: What is it that has passed through, and whose weight amounted to about twenty-five per cent, of the whole residue ? Perhaps Mr. Henderson will be able to enlighten us on one point—that is, does he add anything else besides ammonia to the gelatine, so as to alter in any way the emulsion prepared from “leucine ?" Gelatines are usually acid, so when that acid is neutralised by the ammonia, a salt is found which will pass through the septum. In conclusion, if green fog, frilling, or any other drawback in gelatino-bromide emulsion be due to decomposed gelatine, do not imagine you will remove it by simply washing; but if you use either the precipitation method by means of alcohol, or adopt Mr. Burton’s efficient method of allowing the precipitate to subside, and then decant the useless gelatine, you will conquer your difficulty. PHOTO-MICROGRAPHY. BY Q. J. JOHNSON.* Photo-micrography, or the process employed in photographing the magnified images of microscopic objects, has been practised in France, Germany, England, and America for some years to a more or less limited degree, but of late has received a great impulse from the facilities afforded by rapid gelatine dry plates for the practice of the art by ordinary artificial light. Under the wet collodion system the sensitiveness of the film was too slight for practical use with the lamp or gas, and few cared to encounter the somewhat precarious opportunity afforded in this climate by the happy conjunction of leisure and sunshine. Too often has the writer been victimised when, counting on a morning’s holiday, and having made all due preparation, the sun has unceremoniously withdrawn his face just as the sensitized plate was placed in the camera, and for weeks together has refused to reappear at an opportune moment. The finest specimens of the art that I have seen were executed by Dr. Woodward, Surgeon-General of the United States Army, and residing at Washington, who has devoted much attention to the subject, and who evidently has been furnished by his Government with ample funds for carrying out his investiga tions. His apparatus is of the most complete description, an apartment being fitted up for the express purpose of taking photo-micrographs, a heliostat provided, and lenses ground specially by Wales and others for accurate microscopic and photographic delineation. A report, fully illustrated, was pub lished a few years ago by the American Government, containing the results of the labours of this scientist and his coadjutor, Dr. Curtis. Besides portraying such objects as diatoms, the nature of the delicate markings on which has been the subject of so much controversy in past years, these gentlemen have photographed numbers of pathological subjects, which, however, present great difficulties to the photographer on account of the want of penetration in microscopic lenses. Mr. J. B. Dancer, the well-known Manchester optician, as long ago as 1840, produced photographs of microscopic objects, the image of a flea and other subjects being taken on silver plates. The first photographic illustrations of microscopic objects published in this country appeared in the Quarterly Journal of Microscopic Science in 1853, vol. 1., since which period many works have been illustrated by means of these beautiful prints. Besides Dr. Woodward, the names of Drs. R. L. Maddox, Abercrombie, Wilson, and Redmayne, and of Messrs. Wenham and Sliadbolt, have for long been connected with a successful pursuit of the art. A specimen of the work of Dr. Maddox, of London, who photographed the objects delineated in the frontis piece of Dr. Beale’s work on the microscope, now lies on the table. Mr. York has also just published a series of transparen cies of micro objects suitable for lecture illustration. I have also prints of diatoms from negatives taken by Fritsch and Muller, of Germany, and published by Williams and Norgate, 14, Henrietta Street, Covent Garden, London. One of the prints is a magnified representation of the set of diatoms so marvel lously prepared by Moller, ot Schleswig-Holstein, and known as the “ typen platte,” or type plate. It contains 100 specimens of these beautiful organisms, which are now classed under the vege table kingdom, and which are found both in a fresh and fossil state over the whole world, and any stagnant pond, running • A communication to the Manchester Photographic Society.
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